775 FXUS66 KSEW 110333 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 833 PM PDT Tue Sep 10 2024 .UPDATE...Showers are moving into Puget Sound this evening with activity continuing through tonight. An isolated thunderstorm or two is still possible later tonight into Wednesday morning, especially for southern areas and along the coast, but the threat is generally limited. No major forecast updates this evening. && .SYNOPSIS...A more fall-like pattern is setting up for the rest of the week as a series of low pressure systems move through the area. A passing disturbance brings widespread rain tonight through Wednesday, with the potential for an isolated thunderstorm as it moves eastward through Wednesday. Expect cooler temperatures and abundant cloud cover to continue through much of the week ahead with occasional shower chances. A stronger front may arrive by late Monday or Tuesday. && .SHORT TERM /TONIGHT THROUGH SATURDAY/...Clearing skies this afternoon with temperatures around 70 through much of the interior at this hour. Meanwhile, increasing clouds are already moving onto the coast and across the Olympic Peninsula ahead of the next approaching frontal system. Expect this to bring some leading light rain to the coast by sunset tonight and into the Puget Sound region later overnight. Rainfall totals will generally be around a half inch for the coastal areas and mountains, with closer to a quarter inch for the remainder of the lowlands from around Seattle southward. With the cooler air mass moving in, expect that the upper elevations of Mount Rainier (but not expected down at Sunrise or lower elevations). Temperatures will be quite cool as a result of the rain and clouds, with temperatures Wednesday only topping out in the 60s for many locations. As the low tracks inland, expect to see steepening lapse rates that could support a few isolated thunderstorms. Any storms that develop are likely to pulse up and down quickly with gusty winds and lightning the primary hazards, and the chances will be highest near the coastal waters and coastline and south of Puget Sound. A brief break in the showers and less cloud cover is expected Thursday as the heights rise a bit in between the weather systems. This will allow temperatures to nudge a couple of degrees warmer, or closer to 70 degrees for daytime highs. Not much change to the overall pattern into Friday. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...The region is likely to remain in a cool and cloudy pattern with a return of precipitation chances over the weekend and into the start of next week. The weekend doesn`t appear overly wet though, without a strong signal for a focused round of heavier rain. The next front that approaches late Monday into Tuesday will then likely bring the next round of widespread precipitation to the region with the ensemble guidance supporting another deeper trough moving across the Pacific Northwest. Cullen && .AVIATION...Southwesterly flow aloft continues over western Washington as a trough digs into the region. Showers are beginning to work their way onshore as a surface low pressure system moves in from the west. Showers will continue to fill in across the region tonight then decreasing in coverage Wednesday morning. Ceilings remain VFR across the region this evening, but will lower into MVFR to IFR at times tonight into Wednesday morning as the front moves through the area. Visibility will be temporarily reduced in heavier rain. There is a low chance for some thunderstorms tonight across the southwest portions of the region, mainly offshore, though potentially affecting KHQM. As shower activity tapers off, expecting ceilings to be able to raise to low-end VFR late Wednesday afternoon into Wednesday evening. Winds will be out of the southwest through tomorrow morning at 4 to 8 kt, becoming northwest less than 6 kt late Wednesday afternoon/evening. KSEA...VFR conditions this evening as showers begin to approach the terminal. Ceilings are expected to drop to MVFR early Wednesday morning. Occasional reductions in visibility are possible in heavier showers. Ceilings then lift to low-end VFR Wednesday afternoon. Southwest winds 5 to 8 kt Tuesday night/Wednesday morning will become northwest less than 6 kt. LH && .MARINE...A low pressure system centered just offshore will move through the region tonight into Wednesday. Rain showers will continue across the coastal waters through Wednesday, with a few isolated thunderstorms possible late tonight into early tomorrow morning. These may produce gusty winds up to 30 kt within a 2 to 4 hour window (best chance 9 PM to 2 AM over the coastal waters), for which a Marine Weather Statement has been issued. Once the trough moves through, high pressure will rebuild offshore for the second half of the week with weak onshore/northwest flow over the waters. The next possible disturbance will move through the region this weekend, but the threat of any impactful winds is low. Seas tonight will increase to 3 to 5 feet, further increasing to 5 to 7 feet by Wednesday night/Thursday before dropping back to 3 to 5 feet through rest of the week. HPR/LH && .FIRE WEATHER...An upper low pressure system moving in just south of the area will spread rain showers into this area this evening through Wednesday evening. Instability associated with the low pressure trough, and the diffluence aloft, will generate a slight chance of a few isolated lightning strikes for the southern half of western Washington. There is a 50 to 75 percent chance of a wetting rain for the same area. JBB && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$

053 FXUS66 KPQR 110333 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 832 PM PDT Tue Sep 10 2024 Updated aviation discussion .SYNOPSIS...Warm and dry through this evening ahead of an approaching system. A soaking rain is expected tonight into tomorrow (Wednesday) as the system arrives. Expect a 20-40% chance of thunderstorms across the area, with the highest chances along the coast and Coast Range. Conditions dry up by Friday. Saturday through early next week, another trough will return widespread rain chances. Onshore flow maintains temperatures near or slightly below normal. && .SHORT TERM...Now through Thursday night...Satellite imagery as of 230 PM PDT reveals our next low pressure system centered about 300 miles offshore of British Columbia, around 49.63N 133.85W. Expect conditions to remain dry and warm through this evening across NW Oregon and SW Washington before this system arrives tonight. High clouds will gradually filter in this evening as the system moves closer to the Pacific Northwest. Afternoon highs remain forecast in the upper 70s to low 80s for interior valleys and 60s along the coast the higher terrain. Persistent onshore flow will also maintain breezy conditions through the Columbia River Gorge, with westerly winds gusting to 20-25 mph through early evening. The upper level low will approach the coast tonight and move overhead tomorrow (Wednesday), bringing more fall-like temps and a widespread soaking rain to the region through Wednesday evening. HREF/CAM guidance suggests that precipitation from the system will arrive along the coast between 5 to 8 PM this evening and reach the Willamette Valley after 11 PM/12 AM tonight. With colder air moving in aloft, lapse rates will steepen and the atmosphere will become more unstable. As a result, will see a 30-40% chance of thunderstorms along the coast and Coast Range, and a 15-30% chance of thunderstorms for locations east of the Coast Range beginning tonight. Thunderstorm chances continue through Wednesday afternoon since clearing behind the system could allow for further instability as daytime heating occurs. Since abundant rainfall is expected to accompany any storms that do form, this will minimize the threat of any new fire starts. The majority of precipitation is expected to fall overnight through mid-morning Wednesday. Additional precipitation after mid-morning Wednesday will depend on where thunderstorms form. Any passing thunderstorms have the potential to bring heavier rain rates. Even though you might see increased clearing of clouds during the day tomorrow, be aware that a thunderstorm could develop nearby and move quickly into your area. Our current 24 hr precipitation forecast from 11 PM Tuesday to 11 PM Wednesday is around 0.40-0.70 inch for interior valleys, except lower amounts (less than 0.25 inch) closer to the central Columbia River Gorge and Upper Hood River Valley. For the coast, Coast Range, and Cascades, forecast amounts are between 0.50 to 1.25 inch, with the highest amounts in the mountains where westerly flow could lead to orographic enhancement of precipitation. Will note that no significant hydro concerns are expected with this rainfall given the recent dry weather and with rivers running at typically low late summer levels. Wednesday will also be the coolest day of the week, with below normal temperatures expected as inland highs struggle to make it out of the 60s. Thunderstorms will taper off Wednesday evening as the system moves further east. However, will maintain a chance of showers over the region through Thursday afternoon, especially for orographically favored locations in the higher terrain of the Cascades. Additional rainfall amounts will be minimal as ensemble 24 hr QPF amounts ending 11 PM Thursday are generally below 0.20 inch in the Cascades and less than 0.10 inch west of the Cascades. -Alviz/CB && .LONG TERM...Friday through Monday...The region is forecast to dry out completely by Friday as shortwave ridging moves overhead. Afternoon highs on Friday are forecast to rebound into the low to mid 70s as a result. After that, the majority (80%+) of ensemble members from WPC cluster analysis hints at another trough entering the region, bringing additional precipitation chances Saturday through early next week. Onshore flow remains in place through next week, maintaining benign conditions and keeping temperatures at or just below seasonal normals. -Alviz/CB && .AVIATION...An upper level trough offshore will continue to dig toward the Pacific NW tonight and move inland on Wednesday. This will cause flow aloft to transition from southwesterly tonight to northwesterly late Wednesday. A front associated with the low pressure system will bring increasing rain across the area from northwest to southeast through Wednesday morning. As of 02Z, rain has begun at KAST and will continue to spread inland overnight. Widespread VFR conditions expected to gradually deteriorate tonight as CIGs lower and heavier rainfall rates reduce visibilities. Latest statistical guidance suggests probabilities for MVFR ceilings climb abruptly between 04-06z Wednesday along the coast and in the 10-12z timeframe for the Willamette Valley. High resolution models do suggest a nearly 50% chance for IFR conditions near frontal passage along the coast between 06-10z Wednesday, particularly around KONP. Expect most TAF sites to transition into VFR thresholds between 19z-21z Wednesday with only brief and sporadic dips into MVFR and IFR thresholds under or near stronger showers thereafter. There is also a 25-40% chance for thunderstorms along the coast tonight and lesser chances inland. A second window for thunderstorms (15-30% chance) appears to exist for inland TAF sites Wednesday afternoon, particularly between 21z Wednesday and 03z Thursday. PDX APPROACHES...Expect VFR conditions to give way to lowering ceilings and rain showers overnight. Latest statistical guidance suggests probabilities for MVFR ceilings climb abruptly in the 10-12z timeframe. The probability for conditions to deteriorate into IFR thresholds at any given hour only peaks at around 30% in the 13-16z Wednesday timeframe. Conditions should gradually trend into predominantly VFR thresholds between 19-21z Wednesday. Note there is a 15-25% chance for a thunderstorm tonight and a 20-30% chance for a thunderstorm Wednesday afternoon and evening, primarily between 21z Wednesday and 03z Thursday. DH/Neuman && .MARINE...A front will slide southeastward across the waters overnight. While winds look to generally remain below Small Craft Advisory thresholds, the latest high resolution model guidance suggests a relatively high probability (60-80% chance) for 1-2 hours of winds gusts in excess of 21 kt. In addition, thunderstorms over the waters could bring locally stronger wind gusts although the probability that any given spot receives a Gale Force wind gust of 34 kt or higher is well less than 10%. High pressure returns to the northeast Pacific late in the week and brings a brief period of northerly winds Friday. At this point, there is a 20% chance that winds of greater than 21 kt work their way northward into the waters off the central coast of Oregon Friday afternoon and evening while winds will be even weaker farther north towards the mouth of the Columbia River. Uncertainty in the forecast details and timing of storm systems grows thereafter, but another low pressure system and attendant front or two will drop southeastward across the waters during this time. Given the relatively weak winds across the waters over the next week, expect seas to generally hover between 4-7 ft through early next week. /Neuman && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland

728 FXUS66 KMFR 110529 AFDMFR Area Forecast Discussion National Weather Service Medford OR 1029 PM PDT Tue Sep 10 2024 Updated AVIATION Section .DISCUSSION...The leading edge of the storm system expected to move through the area on Wednesday is now entering the PacNW. Satellite imagery is showing some mid and high level cloudiness advancing across Washington and Oregon and precipitation is pressing southeastward from the northeast Pacific and moving into NW Oregon (raining in Astoria). Radar is showing some light returns along the central Oregon coast at this hour, extending south-southwestward into our northern coastal marine zones. It won`t be long before precipitation arrives at the Coos Coast, probably around or just after midnight. Models continue to show convectively enhanced bands of showers moving onshore overnight into Wednesday morning; some of the stronger cells or elements within the bands could bring thunderstorms with brief downpours and gusty winds. These will spread inland by around daybreak reaching most areas north and west of the Rogue-Umpqua Divide by 5 am, then to the Grants Pass/Medford/Ashland area around 6-8 am, to the Cascades by 9-10 am and over the east side by midday. Widespread wetting rainfall is expected with the most rain occurring along the coast (in the coast ranges) and also across the Umpqua Valley to the Cascades/Foothills. These areas will see widespread amounts of 0.40-0.80", locally near an inch in some spots. Lesser amounts are expected south of the Umpqua Divide and east of the Cascades in Oregon with 0.10-0.40". This is welcome news and will provide needed rain to many of the wildfires burning in the region. It should be noted that rainfall rates could be significant within the strongest convective cells, but these cells will be moving very quickly and sustained heavy rates shouldn`t last too long in any given location. As such, we aren`t too concerned about flash flood/debris flow risk. Latest CAM guidance is showing potential for rates in the 0.20-0.30"/hr range. This is mainly across Douglas County for a few hours Wednesday morning. Showers will continue through Wednesday afternoon and it will be much cooler compared to the recent spell of heat/warmth. Temperatures will struggle to reach 70F here in Medford (still officially forecasting 69F). I should also note that not everyone in the area will get precip tomorrow. Portions of the Shasta Valley or portions of the Mt Shasta region might get missed all together since the best forcing for precipitation is focused to the north in Oregon. By Wednesday evening, the upper trough axis will shift to the east and coverage of showers should diminish rapidly. Onshore flow, however, will keep PoPs higher along the coast and over to the Cascades. Things dry out on Thursday as heights rise and precip chances gradually diminish to nil across NW sections. Expect increasing sunshine and a comfortable afternoon with highs largely in the 65-75F range. It will up a bit again Friday and Saturday with temperatures closer to normal. -Spilde && .AVIATION...11/06Z TAFS...An approaching front and upper trough will bring widespread showers overnight and through the day Wednesday. Overall, expect a mix of VFR/MVFR. Showers may locally lower visibilities and ceilings as well as obscure elevated terrain. Additionally, thunderstorm chances will be present across the area through Wednesday. The highest chances (25-40%) will be over Coos/Douglas counties, with lesser chances (20-25%) across the rest of the area. Brief downpours and gusty winds could accompany any of the stronger cells. Shower coverage will diminish Wednesday evening. -Spilde && .MARINE...Updated 200 PM Tuesday, September 10, 2024...Northerly winds will calm tonight as a thermal trough weakens. A Small Craft Advisory remains in place through 8 PM tonight. A low pressure system will approach the area early Wednesday morning, bringing showers across area waters. The first showers will arrive early Wednesday morning and continue into Wednesday night. Thunderstorm chances will also be present over area waters. The highest chances (25-40%) will be north of Cape Blanco, with lesser chances (15-30%) south of Cape Blanco. These chances will start to dissipate early Wednesday evening. Westerly swell will follow the low pressure system on Thursday, but will not be strong enough to bring Advisory level seas. A thermal trough will redevelop Thursday evening into Friday morning, bringing elevated northerly winds especially south of Cape Blanco. Currently, a Small Craft Advisory is in place for Thursday at 5 PM through Friday at 5 AM for waters south of Cape Blanco, with further Advisory level seas likely to follow through Saturday morning. Guidance also suggests localized areas very steep and hazardous seas south of Gold Beach, not currently not with enough consistency to support a Hazardous Seas product. -TAD && .PREV DISCUSSION... /Issued 514 PM PDT Tue Sep 10 2024/ DISCUSSION...An upper low off the British Columbia coastline continues to move almost due south toward the Pacific Northwest coastline this afternoon. This resulted in a subtle cooling trend...with temperatures generally 2 to 6 degrees cooler across the region compared to this time yesterday. Surface onshore flow continues to push most of the wildfire smoke east of the region...resulting in mostly clear skies across the area. A very sharp change in the weather is expected tomorrow as the low continues south and moves onshore along the OR/WA boarder Wednesday late morning/early afternoon. This will bring rain to the coast as early as around midnight tonight...spreading east...impacting the entire area by early afternoon on Wednesday. Additionally...there will be a slight chance to a chance (15 to 25% probability) of thunderstorms across the region much of the day...both ahead of the front...and behind the frontal passage with convective showers. Most of the activity is expected to push east out of the region Thursday morning...with lingering activity across Douglas and Coos county and the Cascades into the late morning/early afternoon hours. There will also be a sharp cooling trend tomorrow...with temperatures between 15 and 20 degrees cooler compared to this afternoon. A little taste of Fall for the area! Once the activity shifts east...we will experience a warming trend as a weak upper ridge builds over the area Friday with zonal flow during the first part of the weekend. Temperatures will rebound to near normal levels for the middle of September Friday and Saturday with the area expected to be dry. A return to unsettled weather is in store during the second half of the weekend into the first part of next week as upper level troughing remains dominant over the Pacific Northwest. We do have a lot of confidence in the fact that we will see cooler than normal temperatures with this pattern. We will also see precipitation...but timing is still uncertain at this point. All of the clusters...starting day 5...do indicate that we will remain in a trough pattern...with subtle location differences between each cluster...resulting in uncertainty in timing and location of precip...but high confidence in cooler than normal temperatures. To continue the Fall temperature trend...our friends at the Climate Prediction Center indicate in the 8 to 14 day outlook (valid September 18th through 24th) that we can expect below normal temperatures and above normal precipitation. Stay tuned for additional details as we get closer to mid to late September! -Riley AVIATION...11/00Z TAFS...Aside from wildfire smoke limiting visibility in the vicinity of active fires, VFR will prevail area wide this evening. An approaching front and upper trough will bring widespread showers late tonight and through the day Wednesday. Showers may locally lower visibilities and ceilings as well as obscure elevated terrain. Additionally, thunderstorm chances will be present across the area through Wednesday. The highest chances (25- 40%) will be over Coos/Douglas counties, with lesser chances (20- 25%) across the rest of the area. Shower coverage will diminish Wednesday evening. -Spilde MARINE...Updated 200 PM Tuesday, September 10, 2024...Northerly winds will calm tonight as a thermal trough weakens. A Small Craft Advisory remains in place through 8 PM tonight. A low pressure system will approach the area early Wednesday morning, bringing showers across area waters. The first showers will arrive early Wednesday morning and continue into Wednesday night. Thunderstorm chances will also be present over area waters. The highest chances (25-40%) will be north of Cape Blanco, with lesser chances (15-30%) south of Cape Blanco. These chances will start to dissipate early Wednesday evening. Westerly swell will follow the low pressure system on Thursday, but will not be strong enough to bring Advisory level seas. A thermal trough will redevelop Thursday evening into Friday morning, bringing elevated northerly winds especially south of Cape Blanco. Currently, a Small Craft Advisory is in place for Thursday at 5 PM through Friday at 5 AM for waters south of Cape Blanco, with further Advisory level seas likely to follow through Saturday morning. Guidance also suggests localized areas very steep and hazardous seas south of Gold Beach, not currently not with enough consistency to support a Hazardous Seas product. -TAD && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Air Quality Advisory in effect until 5 PM PDT Wednesday for eastern Douglas, northern Klamat and northern Lake counties. CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT this evening for PZZ350-356-370-376. Small Craft Advisory from 5 PM Thursday to 5 AM PDT Friday for PZZ356-376. && $$ MAS

000 FXUS66 KEKA 102151 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 251 PM PDT Tue Sep 10 2024 .SYNOPSIS...An approaching upper trough will drive inland temperatures much cooler and bring chances for light rain and breezy conditions Wednesday. Additional chances for precipitation look probable in the extended forecast. && .DISCUSSION...The marine layer will begin deepening with an approaching upper trough and frontal system, lessening the chances for fog development along the coast tonight. With the dropping heights, inland temperatures are trending to below average levels. Daytime highs will sharply drop by 15 to up to 19 degrees Wednesday with the passing of the cold trough. There is a high probability (70- 95%) for a wetting rain of at least a tenth of an inch from N Humboldt through Del Norte Wednesday. Del Norte County, including its interior, has a 50 to 75% chance for a quarter inch of greater in a 6 hour period early Wednesday morning. Forcing, steepening lapse rate and weak instability may allow for convective showers, although latest model soundings are not supportive of thunderstorm development. Chances for a wetting rain quickly drop off going south into Mendocino County. This system will begin increasing northwesterly to westerly winds this afternoon, and especially tonight through Wednesday night. There is a solid signal for maximum wind gusts around or over 30 mph Wednesday morning through Wednesday night in far SE Mendocino and Lake counties (70-80%). There is also a moderate chance (53-63%) for wind gusts to exceed 35 mph late Wednesday in far south Lake County. There will be fire weather concerns in Lake County during the transition to a more moist airmass. Deterministic models have been well aligned for the pattern to persist with additional troughing and precipitation chances into the weekend, and there is robust ensemble and cluster support for this scenario. /JJW && .AVIATION...Coastal stratus brought LIFR TO IFR conditions to many coastal airfields through the day with minimal improvement and only isolated areas observing scattering ceilings. Some scattering is still possible early this evening, especially along the Mendocino coast. Otherwise ceilings and visibilities are expected to deteriorate after sunset for coastal airfields like KCEC and KACV. As the cold front will crosses through the region early Wednesday morning, the marine layer is expected to deepen with the potential for light rain showers, mostly for areas north of Mendocino County. Additionally, a slight chance for a thunderstorm is possible across Del Norte County Wednesday morning. Interior areas will most likely see VFR through the TAF period. /kmz && .MARINE...North winds will ease slightly this evening as a frontal boundary weakens the pressure gradient and then brings a brief round of south/southwest winds across the northern waters early Wednesday morning. That said, gusty winds near 30 kt will persist across the southern waters this evening before frontal passage. As a result, a shortlived small craft advisory was hoisted for the southern inner waters as gusts near 30 kt impact nearshore. Some isolated gale force gusts will even be possible near Cape Mendocino. Otherwise marine winds decrease briefly on Wednesday before north winds ramp up to 15 to 25 kt again late in the work week. As for the sea state, steep seas around 5 to 7 feet this evening will subside slightly into Wednesday as a northwest wave system dominates the marine environment. Steep seas will build again in response to the winds later this week with wave heights peaking near 7 to 9 feet across the outer waters. /kmz && .FIRE WEATHER...An upper trough will begin approaching the region late Tuesday. There is a high probability (70-95%) for a wetting rain of at least a tenth of an inch from N Humboldt through Del Norte Wednesday. Del Norte County, including its interior, has a 50 to 75% chance for a quarter inch of greater in a 6 hour period early Wednesday morning. Chances drop below 15% in northern Mendocino County Wednesday. The cold trough will drop inland daytime highs by a solid 15 to 19 degrees Wednesday. Thunderstorms may also be possible in Del Norte Wednesday, although guidance has been trending away from development. Northwest winds will begin to increase Tuesday afternoon, and will peak on Wednesday when gusts over 30 mph are likely (70-80%), mainly in Lake County, but also southern Mendocino County. RH values have dropped in the mid teens to upper 20s this afternoon, and winds are expected to mildly tick up over the next few hours. There is some uncertainty as to how fast this environment can moisten up Wednesday in Lake County with the peak winds, but minimum RH values in the mid to upper 30s are forecast. This will be sufficient for critical fire weather conditions to occur...but there is low confidence on the duration. /JJW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Wednesday for PZZ455. Small Craft Advisory until 3 PM PDT this afternoon for PZZ470. Small Craft Advisory until 9 AM PDT Wednesday for PZZ475. && $$ Visit us at https://www.weather.gov/eureka Follow us on Facebook and Twitter at: https://www.facebook.com/NWSEureka https://www.twitter.com/NWSEureka For forecast zone information see the forecast zone map online: https://www.weather.gov/images/eka/zonemap.png

293 FXUS66 KMTR 110221 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 721 PM PDT Tue Sep 10 2024 ...New AVIATION... .SYNOPSIS... Issued at 246 AM PDT Tue Sep 10 2024 A gradual cool down today as temperatures cool aloft, before a deep upper level trough brings breezy winds by Wednesday and Thursday. Temperatures will continue to run near to below seasonal averages through the upcoming weekend. && .SHORT TERM... (This evening through Wednesday) Issued at 109 PM PDT Tue Sep 10 2024 The ridge that brought above normal temperatures and near critical fire weather conditions will continue to flatten, allowing for temperatures to return to normal to 5-10 degrees below normal. Tomorrow will be much of the same temperature and cloud cover wise with a deep marine layer of 3,000 feet easily capable of filling in all but the highest of elevations overnight and dissipating by the afternoon. Now for the main hazard: wind. Tomorrow will be very windy as a low pressure system from the Gulf of Alaska drops into the Pacific Northwest, tightening the pressure gradient between subtropical high pressure over the Eastern Pacific Ocean. While below Wind Advisory criteria, widespread wind gusts of 30 mph are expected with gusts of 50+ mph expected through gaps, passes, and other favorable spots, namely the Altamont Pass and Salinas Valley. Actions to take: -Store or secure loose items such as patio furniture, sports equipment, trampolines, and trash cans. -Use caution when driving, especially high-profile vehicles. -Have a plan in case of a power outage. While the overall fire threat is on a downward trend due to lower temperatures and higher relative humidities, fuels still remain critically dry with large fires possible. Therefore, any fire that starts will have no problem spreading and the strong winds will only make matters worse. As always, it is imperative to remain vigilant when it comes to exercising fire safety. Actions to take: -Properly discard cigarettes. -Keep vehicles off of dry grass. -Avoid activities with open flames or sparks. -Avoid power equipment that creates sparks. -Obey burn bans. && .LONG TERM... (Wednesday night through next Monday) Issued at 109 PM PDT Tue Sep 10 2024 Winds will decrease Wednesday evening as the trough axis moves inland and high pressure begins to rebuild. As the trough moves continues East, there may be a brief period of offshore N or NE winds in the North Bay Friday morning. While this possibility remains, the latest model trends are backing off and beginning to favor a more shallow feature that won`t disrupt the standard NW flow. A small amplitude ridge will move trough on Friday, before a second trough slowly approaches from stage left. The exact impacts from this second trough are still uncertain with quite a bit of model divergence, particularly in the timing. There is a decent chance for a bit of rain, but that could be anytime from late Monday-Thursday and the details are too fuzzy to lay out in any great detail at this time. What we do know is that this troughing pattern will keep temperatures mild through the next 7-10 days at least. && .AVIATION... (00Z TAFS) Issued at 721 PM PDT Tue Sep 10 2024 Evening satellite imagery and surface observations show coastal stratus /IFR-MVFR/ moving inland on onshore winds. The SFO-SAC pressure gradient predominates at 3.9 mb and is forecast to strengthen Wednesday afternoon to near 5 mb. Otherwise stratus is forecast to lift and mix out Wednesday morning with lower level cool air advection on increasingly gusty northwest winds. Vicinity of SFO...Satellite imagery and 5 minute observations show stratus /MVFR/ arriving at the terminal, brought in by a gusty west wind. IFR-MVFR tonight to 15z Wednesday morning then VFR for the remainder of the daytime. West wind gusts near 30 knots until 04z this evening, decreasing to 15 knots tonight and Wednesday, increasing to 25 to 35 knots beginning 21z Wednesday and lasting through the evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Stratus clouds are spreading over the Monterey Peninsula, further areal coverage of stratus /MVFR/ is forecast through the evening. IFR-MVFR tonight and Wednesday morning then VFR late morning and afternoon Wednesday. West to northwest winds 10 to 20 knots early to mid evening, decreasing to around 5 knots tonight then increasing to 10 to 20 knots Wednesday late morning and afternoon. && .MARINE... (Tonight through next Sunday) Issued at 440 PM PDT Tue Sep 10 2024 Breezy winds are arriving and will spread across the waters through the night. Expect widespread moderate and gusty north to northwest winds and rough waves across the coastal waters for Wednesday. A gale watch has been issued for possible gale force gusts across the Monterey Bay and inner coastal waters extending from Pigeon Point to Point Pinos Wednesday morning into Wednesday afternoon. Unsettled conditions are expected to continue through the end of the week, but winds reduce in the late weekend. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM Wednesday to 3 AM PDT Thursday for SF Bay N of Bay Bridge. Small Craft Advisory from 9 AM to 3 PM PDT Wednesday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm. Gale Watch from Wednesday afternoon through Wednesday evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm. Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt Reyes 0-10 nm. Small Craft Advisory from 9 AM to 9 PM PDT Wednesday for Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 AM Wednesday to 3 AM PDT Thursday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 3 AM to 9 AM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory until 9 AM PDT Thursday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...Sarment LONG TERM....Flynn AVIATION...Canepa MARINE...Murdock Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea

371 FXUS66 KOTX 110504 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1004 PM PDT Tue Sep 10 2024 .SYNOPSIS... A low pressure pattern will usher in a significant change in the weather, leading to chances for showers and much cooler temperatures Wednesday and Thursday. Temperatures will reach the 60s and 70s. The weekend looks to be on the drier side with seasonal temperatures. && .DISCUSSION... Today through Thursday: Low pressure off the Pacific NW coast will move inland and across the region over the next 48 hrs. We will see a significant cooling trend with temperatures in the 60s-70s Wednesday and Thursday. In addition, this system will bring rain chances to the Inland Northwest. Showers will initially increase across the Cascades and far southeastern WA into the lower Idaho Panhandle later tonight. Shower chances will expand across the rest of our forecast area during the day Wednesday. As the storm pushes eastward Thursday, the best chances for rain will be across the ID panhandle and far eastern WA. Throughout the event, rainfall amounts are not expected to be terribly great, with the best chances for >0.50" mostly confined to northern ID. Friday through Tuesday: Weak ridging returns on Friday, though this will be short-lived in advance of the next approaching system. Regardless, Friday through Monday look generally dry with any light precip chances generally confined to the mountains. Near seasonable temps to also persist. Extended models show more consistency in bringing a stronger trough for Tuesday onward, and more widespread precip chances have been brought into the forecast for this period. /KD && .AVIATION... 06Z TAFS: Trof of low pressure working its way into the region will result in periods of mid-high clouds today. After 06z...light elevated showers to develop along with lowering cloud bases. Main chances for showers through 12Z will be from Ellensburg to Omak and also the Palouse to North Idaho. Better chances develop area- wide after 12Z. Also expect breezy to gusty winds through the Cascade Gaps impacting Wenatchee, Douglas, and Vantage area through the evening. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate to high confidence in VFR conditions. Low to moderate confidence on shower activity resulting in measurable precip at TAF sites. Low confidence for locally reduced visibilities in areas of smoke. /JDC && .PRELIMINARY POINT TEMPS/POPS... Spokane 56 72 52 73 50 75 / 20 40 40 40 20 0 Coeur d`Alene 55 69 51 68 49 73 / 30 50 50 70 30 10 Pullman 53 66 50 65 47 71 / 50 60 50 60 20 0 Lewiston 60 72 56 73 54 78 / 50 70 60 70 20 0 Colville 53 71 50 73 43 76 / 20 50 40 30 10 0 Sandpoint 53 66 51 65 47 68 / 20 60 50 80 50 30 Kellogg 54 64 50 59 50 68 / 50 80 70 90 60 40 Moses Lake 57 73 52 76 48 77 / 20 40 10 0 0 0 Wenatchee 57 70 52 74 52 77 / 40 50 10 0 0 0 Omak 57 74 51 79 50 80 / 30 50 20 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$

617 FXUS66 KPDT 110527 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1027 PM PDT Tue Sep 10 2024 .UPDATED AVIATION...06Z TAFs...VFR conditions will prevail through the forecast period. Primary weather will be rain showers that will occur over all TAF sites today. DLS will continue to see breezy conditions through 12Z with sustained winds of 12kts and gusts to 20kts. Winds today will be primarily from the west to northwest and below 10 kts. Haze may continue to linger over BDN/RDM from area wildfires but VIS should remain P6SM. Bennese/90 && .PREV DISCUSSION... /issued 444 PM PDT Tue Sep 10 2024/ SHORT TERM...Tonight through Thursday...An upper level trough approaching the region from the Gulf of Alaska is beginning to dominate the weather pattern. Currently it has the region under a southwest flow as a closed upper level drops down the Canadian coast. Some instability in this southwest flow will lead to the development of some showers across northeast Oregon by this evening and overnight with a slight chance of some thunderstorms. This activity will be pushed eastward into Idaho early Wednesday as the closed low moves into western Oregon and Washington late tonight and early Wednesday. This will lead to increasing showers coming over the Cascades after midnight then continuing to spread east through the day and increasing in coverage across most of the forecast area. There will be enough weak instability that there will be some isolated thunderstorms in the afternoon through early evening. Showers will begin to decrease west to east across the forecast area late Wednesday and overnight as the low moves off into central Idaho. A ridge of high pressure will begin moving into the region on Thursday with some lingering showers over the eastern mountains coming to an end late day and evening. Precipitation amounts associated with this system will range from a tenth of an inch or less around the Columbia Basin to a tenth to three tenths of an inch central Oregon to around half an inch over the eastern mountains. Snow levels will be lowering to around 7500 to 8000 feet over eastern Oregon Wednesday night and early Thursday bringing a light dusting of snow to the high mountain elevations. Some breezy winds will accompany this system but with higher humidities and showers which mitigates fire weather concerns. This system will bring much cooler and below normal temperatures conditions across the entire forecast area Wednesday through Thursday. LONG TERM...Friday through Tuesday...The long term will remain progressive in nature as we see a transient upper level ridge move into the region in the wake of the deep low that is bringing the cooling trend over the next few days. But as mentioned, this ridge will be transient, quickly swept out by another deep upper trough that will spin a low into the West Coast and help bring another cool period that will persist through the end of the long term. The long term begins as a weak upper level ridge moves into the region, controlling our weather pattern for most of Friday and Saturday. This should allow for dry conditions and warming temperatures, with highs near to just above normal in the upper 70`s to low 80`s. The NBM shows a probability of temperatures 80+ degrees on Friday at 50-75% for Hermiston, the Walla Walla Valley, and the Columbia basin, with a more widespread 30-70% on Saturday across the majority of our low elevation areas. But that will end our brief heating trend, as a deep upper trough descends along the Canadian coastline and into our region over the later part of the weekend. This will overspread cloud cover Saturday afternoon and evening which will help to deter a more noteworthy warming trend, and we should see a few light chances at showers beginning to move into the Washington Cascades Saturday evening and night. Then on Sunday through Tuesday, troughing dominates our weather pattern, bringing a daily cool down and chances of showers across the whole CWA. Ensemble clusters are in good agreement that we will see widespread troughing, but do show discrepancies in the strength of this feature. Nonetheless, a cooling trend will be the most likely outcome from this feature, with temperatures descending around 3-5 degrees daily during this time. By Tuesday of next week, our highs will peak in the 60`s to low 70`s. The NBM shows only a 30- 60% probability of highs 70+ next Tuesday, primarily in the Columbia Basin. Outside of temperatures, precipitation remains the other noteworthy impact from this system. Average QPF totals from Sunday through Tuesday are currently forecast between 0.1-0.5 inch, highest in the mountains and peaks where just under an inch could be possible, while the lowest totals will be in the Columbia Basin and Kittitas Valley where only 0.01-0.1 inch are expected. Overall rainfall isn`t expected to be heavy, with ensembles indicating our PWAT values will only be at 100-150% of normal. But this should be sufficient to produce at least a shower or two for most of the region, which should continue to be a welcome deterrence ongoing wildfires. Overall there is moderate to high confidence in the forecast (60- 70%) since ensembles present the major features, even if they do show differences in the strength of those features. Goatley/87 AVIATION...00Z TAFs...Aviation concerns revolve around rain chances area-wide and potential for sub-VFR smoke in central OR with a system expected to bring rain chances area-wide late tonight- tomorrow. Latest satellite shows a thick elevated smoke layer affecting central OR around 10 kft, otherwise some growing cu across Klamath-Lake to Union-Wallowa. This smoke layer will continue to affect the area through rest of today. Outside of smoke plumes that are apparent on radar, no showers or thunderstorms at this time. There is potential for isolated thunderstorms through early tonight across the aforementioned area, focused across eastern OR, where there is modest instability. Low chances overall in storms, 10-20%, and no TAF terminals are expected to be affected, though HREF shows a low signal for potential isolated showers affecting the KALW and KPDT terminal late tonight. Tomorrow, increased rain chances spread west to east roughly 12-00UTC with the lowest chances in the Lower Basin. Low-end VFR (less than 7 kft) expected at sites, lower across central OR. The best chances for a tenth of an inch across central OR and eastern Gorge terminals (70%+). Otherwise, light winds pick up to light breezes tomorrow around 10-12 kts with the KDLS, KPDT, and KALW seeing gusts 16-22 kt. && .PRELIMINARY POINT TEMPS/POPS... PDT 54 70 51 71 / 20 50 40 20 ALW 57 74 54 74 / 20 50 40 20 PSC 61 77 58 78 / 10 40 20 10 YKM 56 74 51 76 / 20 50 20 0 HRI 58 75 53 76 / 10 40 30 10 ELN 55 69 52 73 / 30 50 20 0 RDM 49 63 43 66 / 10 80 40 10 LGD 52 68 50 66 / 50 70 70 60 GCD 51 68 46 65 / 20 80 60 20 DLS 57 73 56 73 / 30 70 20 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...91 LONG TERM....87 AVIATION...90

492 FXUS65 KREV 102138 AFDREV Area Forecast Discussion National Weather Service Reno NV 238 PM PDT Tue Sep 10 2024 .SYNOPSIS... * Strong winds will result in widespread critical fire weather conditions and impact recreation and aviation activities on Wednesday. * Near to below normal temperatures expected for the second half of the week with a chance of showers and storms near the Oregon border on Wednesday. * A low pressure system may provide another round of gusty winds, cooler weather, and potential for precipitation early next week. && .DISCUSSION... A robust upper cyclone is evident on the latest moisture-channel imagery as it churns off the coast of British Columbia. This feature will continue to dig southward towards the region through Wednesday morning before ejecting into the Intermountain West states at the end of the week. As it does so, a belt of amplified westerlies will overspread the Sierra and western Nevada on Wednesday, yielding widespread strong winds that will induce impacts to fire, recreation, and aviation. West winds of 15-25 mph with gusts of 30-40 mph (except 60-70 mph along ridgetops) will support critical fire weather conditions (more details in the Fire Weather discussion below), choppy lake waters with wave heights of 2-4 feet, and turbulent arrivals/departures into regional airports much of Wednesday into early Thursday. There is a chance of showers (30-60%) and storms (15-25%) in the northern tier of Lassen, Washoe County and the Surprise Valley Wednesday with drier conditions elsewhere. Temperatures will cool around 6-10 degrees from today with highs in the upper 60s to 70s for Sierra locales, and upper 70s to 80s across western Nevada. Thursday will likely serve as our coolest day of the week before temperatures gradually warm towards seasonal averages during the end of the week and weekend. The latest suite of ensembles hint at another deep trough passage early next week, which would favor yet another bout of gusty winds, cooler weather, and increasing chances of showers and storms. -Salas && .AVIATION... The main weather concern will be increasing winds and subsequent LLWS/mountain wave turbulence issues late tonight through Wednesday. Westerly FL100 winds will begin to strengthen in earnest around 12Z Wed before reaching its apex of 30-40 kts during the 20-03z timeframe. LLWS concerns will be greatest in the morning and evening hours when surface winds are light/becoming light amid stronger winds aloft. In the late morning to early evening, westerly surface gusts will vary from 25-35 kts from area terminals. Winds will weaken Wednesday night into Thursday morning, alleviating LLWS/turbulence issues. -Salas && .FIRE WEATHER... CHANGES TO THE FORECAST: 1) The Red Flag Warning in NV420-Northern Sierra Front (including the Davis Fire) has been upgraded to a **Particularly Dangerous Situation** Red Flag Warning that will go into effect on Wednesday. * Strong west winds with gusts of 40 mph or stronger are expected from the valley floors to the mid-slopes with gusts approaching 60 mph along ridgetops. It is worth reiterating that the wind direction will veer to a predominant westerly direction Wednesday, which is a shift from the antecedent S-SW winds influencing the Davis Fire in the last few days. While afternoon humidity will be somewhat low in this area (15-22%), it will likely remain just above critical thresholds. Regardless, there is high confidence that the winds will prove more than sufficient in compensating for the slightly higher humidities. Winds will subside in the evening across lower elevations, but will likely remain elevated along ridgetops until early Thursday morning. It is paramount to heed instructions from emergency officials and be ready to evacuate, if necessary, especially those near the Davis Fire. 2) We`ve added Red Flag Warnings to Alpine and Mono Counties, as well as the Basin and Range fires zones for Wednesday (NOT designated as a PDS). * A burn environment characterized by west winds of 20-25 mph with gusts to 35 mph and RH of 8-15% is expected to materialize over a 3-6 hour period Wednesday afternoon and early evening, thus warranting a Red Flag Warning for these areas. Otherwise, the forecast remains on track with critical conditions expected into the evening across the Sierra Front today. Strongest gusts up to 30 mph will likely occur from the late this afternoon into the early evening before weakening, except along ridgetops which will remain breezy. As outlined above, Wednesday will be our highest fire risk day, owing to the combination of widespread strong winds and low humidities. For any new or existing wildfires, robust winds in the plume-bearing layer will inhibit significant vertical growth of smoke columns and allow for excellent transport of smoke/smoke particulates towards the east. Much weaker winds, cooler weather and higher humidities will alleviate fire weather concerns for the end of the week. -Salas && .REV Watches/Warnings/Advisories... NV...Red Flag Warning until 8 PM PDT Wednesday NVZ420. Lake Wind Advisory from 8 AM to 8 PM PDT Wednesday NVZ002. Red Flag Warning from 11 AM to 8 PM PDT Wednesday NVZ421-423-429. Lake Wind Advisory from 11 AM to 8 PM PDT Wednesday NVZ004. CA... Lake Wind Advisory from 8 AM to 8 PM PDT Wednesday CAZ072. Red Flag Warning from 11 AM to 8 PM PDT Wednesday CAZ274. && $$

228 FXUS66 KSTO 102256 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 356 PM PDT Tue Sep 10 2024 .Synopsis... Two weather systems impact the area over the next week. First system will bring a slight chance of showers to northern Shasta County Wednesday. Elsewhere, dry conditions and breezy winds at times creating elevated fire concerns. Second system arrives late Sunday and Monday and brings chances of rain (30 to 50% chance) across the area as well as a cool down into the 70s. && .Discussion... Two weather systems will impact the area over the next several days. Main concerns with the first system will be fire weather related with gusty winds. This is from a fairly strong upper low that drops quickly south tonight to the WA/OR area. This will increase westerly flow across the area tonight into tomorrow with gusty winds at higher elevations. Main energy from this upper low pushes across Oregon on Wednesday. Energy from it will remain north, keeping the risk of showers or a stray thunderstorm confined mainly to areas north of our forecast area. THat being side, the northeastern corner of Shasta County may see some light precipitation with NBM showing a 5 to 15% of precipitation with a 10-15% of thunderstorm potential. This system then slides into Idaho Wednesday night into Thursday. It isn`t a classic "inside slider" forecast pattern but enough east/west pressure gradient will bring gusty winds to the western side of the valley on Thursday. Current forecasts project gusts of 20 to 30 MPH along I-5 westward. Probabilities show a 15-30% chance of gusts exceeding 30 MPH, showing further confidence of this not being a traditional inside slider pattern and the stronger winds associated with it. Chances have trended lower from the overnight period as well, so we will continue to monitor if this trend continues. Last concern with winds with this system will be Thursday night into Friday morning as low pulls off to the east. This will allow for east/northeast winds and gap flow winds to develop on our side of the Sierra. We will have Red Flag criteria for a few hours but this will be a fast moving system allowing for humidities to recover after the system`s passage. There is the potential for conditions to exceed current NBM projections as EC Ensemble data shows higher winds for portions of the Sierra. Noting this, NBM 90th percentile was used in the forecast process to merge in chances for stronger wind speeds. && .EXTENDED DISCUSSION (Saturday THROUGH Tuesday)... Increasing confidence in a wet weather system moving down from the Gulf of Alaska, with the addition of cooler temps. EC EFI (Extreme Forecast Index) QPF data for this time period showing some fair Shift of Tail values but low EFI values suggesting a small chance (around 10%) of heavier, localized rain possible. Overall ensemble means have been jumping around a bit that with this next system as latest trends take the upper low very far south eventually into SoCal. There is still a fair amount of uncertainty in rain chances right now but broadly a 30 to 50% of measurable rain at this time. Please continue to monitor the latest forecast for further updates regarding our next weather system. && .AVIATION... VFR conditions over interior NorCal over the next 24 hours. An incoming storm system dropping down from the Pacific Northwest moves inland tomorrow, bringing localized MVFR/IVFR conditions over the Coastal Range and Shasta County mountains. Surface winds will mainly be at or below 12 kts; In the Vicinity Delta, southwesterly winds sustained 15-20 kts gusting 20-25 kts. Localized gusts in the Valley up to 15 kts between 21z-04z Wednesday. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$

696 FXUS65 KMSO 101945 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 145 PM MDT Tue Sep 10 2024 ...Wet Weather System Wednesday Through Friday, Mostly Beneficial Rain With Some Hydrological Concerns and High Elevations Snow... .DISCUSSION...Smoke filled back into many valleys overnight, expect as winds pick up, to see improved visibility and air quality, at least temporarily. As winds die down this evening, smoke will again settle into valleys. By noon on Wednesday, heavy rain showers and thunderstorms develop in north-central ID quickly pushing east into Western Montana. These showers will be capable of 0.50"/ hr rain rates, creating concerns of debris flows from new or existing burn scars. Additionally, areas susceptible to rock or mud slides will also need to be closely monitored, this threat will continue through Friday as widespread precipitation continues. Overnight Wednesday as the low moves south of our region, the mode of precipitation changes from heavy showers to prolonged, widespread rain showers and high elevation snow above 6500 feet. The snow threat will be in a small band just north and west of the low pressure, so exact track of the low matters. Currently, we believe the area to be affected will be the eastern Clearwater Mountains, southern Bitterroots and Sapphires Mountains, Anaconda Range, and Mountains of Lemhi County, ID. Anyone with back country plans should be prepared for wet and raw conditions, and potentially difficult travel conditions at times on high elevation roads. Periods of rain and high elevations snow continues through Friday morning. Hydrological concerns continue to be debris flows from burn scars but increasingly towards rock and mud slides from susceptible areas, such as US-12 Lolo, MT to Lowell, ID and Going to the Sun Road in Glacier National Park. This event should be beneficial to most areas, here are some probabilities for storm totals: Above 0.50" - greater than 80% all of the Northern Rockies. Above 1.00" - 80-90% for the Clearwater, Bitterroot, and Mission Mountains, Rattlesnake Range, and Bob Marshall Wilderness including Glacier National Park. Above 2.00" - 40-50% in the Mission Mountains and Glacier National Park. Saturday and Sunday, a transient ridge is expected to form but not stay. A return to overall troughing, much cooler, and wetter weather system is expected next week. && .AVIATION...Periods of smoke and reduced visibility will continue to be a problem especially from I-90 southward through this afternoon. Afternoon winds will be gusty at 20-25 kts today, but with lower gusts expected in areas stabilized by smoke. A big pattern change to wet and cold conditions will begin on Wednesday as a low pressure system wraps continuous precipitation across the region. Expect showers and thunderstorms at area terminals Wednesday and then lowered ceilings through Friday. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Winter Weather Advisory from midnight Wednesday night to 6 AM MDT Friday for Bitterroot/Sapphire Mountains... Butte/Blackfoot Region. ID... Winter Weather Advisory from midnight Wednesday night to 6 AM MDT Friday for Eastern Lemhi County...Western Lemhi County. && $$

573 FXUS65 KBOI 110247 AFDBOI Area Forecast Discussion National Weather Service Boise ID 847 PM MDT Tue Sep 10 2024 .DISCUSSION...Area fires flared up again this afternoon and evening, with large plumes visible on satellite imagery. The Lava Fire was especially active, with its plume rising to over 35,000 feet. A significant weather pattern shift is still expected for southeast Oregon and southwest Idaho, as a trough from the Gulf of Alaska is forecast to arrive by Wednesday morning. Strong upper-level dynamics are likely to bring showers and thunderstorms along and behind the cold front as early as sunrise Wednesday morning. By 2 PM MDT, thunderstorms will develop along the entire front which is expected to be near the Idaho/Oregon border. Sufficient bulk shear may support rotating updrafts capable of generating large hail up to 1 in diameter, while downdraft CAPE levels suggest the potential for strong gusty winds up to 60 MPH.Temperatures are expected to drop by about 15 degrees from today`s highs, with breezy northwest winds following the cold front. However, there is still some uncertainty regarding the track of the low-pressure center. The ECMWF model is the outlier, showing a more northerly path, while the latest NAMnest also suggests a slightly more northern route then its previous run. Most other guidance continues to favor a more southerly track across the forecast area on Wednesday. This discrepancy affects the location of the heaviest precipitation and potential flash flooding over burn scars. There is a 40-70% chance of receiving more than 0.50 inches of precipitation in the mountains, with a 15-35% chance of exceeding 1.0 inch, particularly in the central Idaho mountains, mainly north of McCall. Burn scars will need close monitoring during thunderstorms for the risk of flash flooding and debris flows. No update needed at this time. && .AVIATION...Scattered showers and thunderstorms beginning in a line near KBKE around 11Z/Wed. and moving into KONO-KEUL-KBOI by 17Z/Wed. Thunderstorms capable of producing outflow winds to 50 kt, and small hail. Low VFR with areas of IFR conditions and mountain obscuration from wildfire smoke. Surface winds: NW-SW 5-15 kt with gusts up to 20 kt. Winds aloft at 10kft MSL: W-NW 15-25 kt. KBOI...Low VFR in smoke. Scattered showers and thunderstorms developing after 20Z/Wed. Surface winds: generally NW 5-10kt, thunderstorms Wed afternoon may produce outflows up to 50 kt. && .PREV DISCUSSION... SHORT TERM...Tonight through Thursday night...A major pattern change is underway across southeast Oregon and southwest Idaho. A trough over the Gulf of Alaska is moving southeastward toward the Pacific NW today and will reach the area by Wednesday morning. Expect increasing clouds to continue with isolated showers and thunderstorms northwest of Baker and Burns OR this afternoon and evening. As the upper level trough approaches, a cold front will move through the area on Wednesday morning in eastern OR and Wednesday afternoon across southwest Idaho. Good upper level dynamics to produce showers and thunderstorms along the cold front and behind the cold front on Wednesday. Thunderstorms will be capable of wind gusts up to 60 mph and hail up to 1" on Wednesday afternoon as effective bulk shear is sufficient for rotating updrafts capable of large hail. Also downdraft CAPE is sufficient for strong gusts. Temperatures will cool around 15 degrees from today and breezy northwest winds expected behind the cold front. Still some uncertainty in the positioning of the low pressure system as it tracks across Idaho, which will determine how much precipitation falls in our area. Shower and thunderstorm chances increase to 50-70 percent in the lower elevations below 5000 feet, and 70-90 percent in the central ID mountains on Thursday. The highest peaks above 9000 feet will see light snow. There is a 40-80 percent chance of exceeding 0.50 inch of precipitation in the mountains, and a 15-35 percent chance of seeing greater than 1.0 inch in the central ID mountains, mainly north of McCall, with this storm system. Recent burn scars will need to be closely monitored during thunderstorm activity for precipitation causing flash flooding and debris flows. Precipitation tapers off on Thursday afternoon as the system pulls away to the northeast. LONG TERM...Friday through Tuesday...A warming trend to near normal with dry conditions expected Friday through the weekend. Another trough arrives on Monday, bringing intermittent showers, thunderstorms, and cooler conditions thereafter. Temperatures fall to around 10 degrees below normal by Tuesday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Red Flag Warning from noon to 9 PM MDT Wednesday IDZ400>403-420-421-423-424-426. OR...Red Flag Warning from noon MDT /11 AM PDT/ to 9 PM MDT /8 PM PDT/ Wednesday ORZ636-637-646. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...JDS AVIATION.....SA SHORT TERM...KA LONG TERM....KA

674 FXUS65 KLKN 102016 AFDLKN Area Forecast Discussion National Weather Service Elko NV 116 PM PDT Tue Sep 10 2024 .SYNOPSIS...A vigorous trough and associated cold frontal boundary will pass through the region on Wednesday with numerous impacts. For today, warm and breezy conditions this afternoon as the trough begins to encroach on the SW CONUS. Wednesday morning winds will increase to critical fire conditions. These strong winds combined with low relative humidity Wednesday afternoon ahead of frontal passage have prompted a Red Flag Warning for most of the CWA save for most of Humboldt county. Humboldt county is excluded due to increasing RH and precipitation chances Wednesday afternoon and evening as the cold front makes its way northwest to southeast into Nevada. Precipitation chances will remain confined to north of Interstate 80 in Humboldt and Elko counties. Best chances for accumulating rainfall will be closer to the Idaho border. Behind the frontal passage late Wednesday night temperatures will fall and result in a chilly Thursday morning. Northwesterly winds behind the front will usher in smoke from Oregon wildfires early Thursday morning. && .SHORT TERM...A strong early fall upper level trough will be the catalyst for a busy short term forecast. On Tuesday zonal flow aloft will begin to increase, slowly at first, and back to a more southwesterly course as the downstream flow of the trough begins its trek into the SW CONUS. Afternoon temps Tuesday in the upper 80s and lower 90s will be the last warm daytime highs for the work week. The trough will amplify overnight into Wednesday and increase wind speeds over the Silver State dramatically by Wednesday morning. This will increase wind speeds throughout the layer and combined with low relative humidity create fire conditions Wednesday afternoon before the front passes through the state. Frontal passage will be gradual over the course of the evening and overnight Wednesday into Thursday. Moisture availability, as expected with a Pacific sourced system, is not in great quantity for the region and confined mainly to the northern extents of the state. Precipitation initiation will begin first in extreme northwestern Humboldt county midday Wednesday. Better instability values associated with the system stay just to the north in Idaho meaning QPF accumulation probabilities of 0.15-0.30 inches will be mainly from scattered showers and isolated convective chances. This will spread more so into Elko county later into the evening as the front traverses further southeast. All layers exhibit a post frontal wind regime by 09z Thursday. Behind the front temperatures will fall overnight into the lower 40s and upper 30s in higher elevations. The northwesterly post frontal flow will also spread smoke and haze from Oregon wildfires into the CWA from north to south early Thursday morning. .LONG TERM...Thursday through next Tuesday. All models are depicting a potent trough moving across the Rockies on Thursday. This will keep the threat for showers and cooler temperatures on tap for the afternoon. Breezy afternoon winds can be expected with gusts to 20 mph, though higher gusts to 25 mph will be felt north of the I-80 corridor. Highs will be 50s and 60s. Clouds and precipitation are expected to come to an end in the evening and clouds will scatter out. A cold overnight is on tap for much of the forecast area due to clear skies. Lows will be in the 30s, though some of the colder locales may see the 20s. Please cover or bring in any sensitive plants to mitigate any effects of cold. A near west to east flow across the forecast Friday will bring dry conditions with moderating, but still below normal temperatures. Overnight temperatures Friday night somewhat with readings in the upper 30s and 40s though the coldest temperatures will be felt over portions of northeast and central Nevada. The flow aloft becomes more southwesterly over northern Nevada by the weekend with the next upstream trough beginning to drop in over the eastern Pacific Ocean. As a result, near normal temperatures are expected Saturday afternoon with upper 70s to low 80s in most valley locations. Lows Saturday night continue to trend warmer with readings in the 30s and 40s. Look for stronger southwesterly flow aloft over the region on Sunday with the approaching west coast trough. Latest forecast guidance begins bringing in low chance PoPs by late Sunday into Monday. Increasing uncertainty Monday and Tuesday with the timing and track of the trough as it moves onshore and through the inter-mountain west. Highs will begin to cool Monday and Tuesday to below normal readings by Tuesday with highs in the 60s and lows in the 30s. && .AVIATION...VFR conditions expected at all terminals over the next 24 hours. VCTS will expected in KELY during the early evening hours with clearing skies during the overnight. For tomorrow, winds SW-W20-25G35KT are possible at all sites through 11/03Z. && .FIRE WEATHER...A well amplified, deep upper level trough containing a vigorous cold front will help to create critical fire conditions for the region Wednesday. For this afternoon elevated fire risks are present due to low relative humidity around 15% and wind gusts between 20 and 30 mph. Tonight as the gradient overhead tightens up due to the encroaching trough, winds will begin to increase in the region by Wednesday morning. Out ahead of the cold front Wednesday relative humidity values will range from 5-15 percent. Strong southwesterly winds well into the 35-45 mph range have prompted a Red Flag Warning from 10AM on Wednesday until 8PM Wednesday evening for zones 424, 425, 426, 427, 438, 469, and 470. Fire zone 437 in northwestern and northern Humboldt county was excluded as higher relative humidity values and earlier precipitation chances associated with the incoming cold front negated need for a warning in that area. The front will pass through the region Wednesday night and will be a mainly dry passage though precipitation may occur in northern portions of the state along the Oregon and Idaho borders. Showers persist in northeast Nevada early Thursday morning before the area dries out in northwesterly flow behind the cold front. && .LKN Watches/Warnings/Advisories... Red Flag Warning from 10 AM to 8 PM PDT Wednesday Central Elko County...Central Nevada-Toiyabe...Eastern Elko County...Northern Nye County-Mojave...Southeastern Humboldt County and northern Lander County...W Elko County, N Eureka and Lander Counties N of I80...White Pine and Northeast Nye Counties. && $$ 99/86/86/99