804 FXUS66 KSEW 210316 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 816 PM PDT Tue May 20 2025 .UPDATE...Showers have pushed into the Cascades with the exception of ongoing convergence zone activity along the King and Snohomish County border. This activity should linger throughout a good portion of this evening and into the overnight hours before tapering off. Otherwise the forecast remains on track and no additional updates have been made tonight. && .SYNOPSIS...Cooler and showery conditions will remain across the region through much of the week as a series of disturbances cross the region. High pressure likely rebuilds over the western U.S. over the weekend, bringing a return of warmer and drier conditions to the area. && .SHORT TERM /TONIGHT THROUGH FRIDAY/...Expect shower coverage to decrease for most overnight, but a developing Puget Sound Convergence Zone will likely maintain an area of steadier showers into Wednesday morning. Some showers increase again near and south of the South Sound later Wednesday, with lingering showers in the Cascades late Wednesday. Transient high pressure moves overhead Thursday with increased sunshine, drier conditions, and temperatures returning back to near normal. .LONG TERM /SATURDAY THROUGH TUESDAY/...The global ensembles generally favor the development and strengthening of a ridge over the western U.S. late in the week and into the weekend. This is a subset, around 20%, of ensemble members that suggest enough of a trough near the region to maintain some clouds and mountain showers, but the majority go favor a drier trend. As a result, the forecast continues to follow this pattern with a warm up - most notably Sunday, with afternoon high temperatures well into the 70s and approaching 80 in the warmest spots. It`s worth noting that there`s is still a portion of ensemble members that would keep temperatures much closer to (or below) normal values. Confidence remains low into the start of next week with some potential for the next frontal system to make its way into the region, but the ridge may remain present and amplified enough to keep warmer and drier conditions for first half of next week. && .AVIATION...Northwesterly flow aloft as scattered showers continue throughout the region this evening. Scattered showers are expected to continue this evening, which could bring localized pockets of reduced ceilings and visibility briefly at times. A convergence zone around KPAE this evening will continue to bring localized lower ceilings, but will slowly dissipate into the overnight hours. Showers will gradually taper off tonight. Ceilings will drop to MVFR Wednesday morning along the majority of Puget Sound terminals (KPWT may drop down to IFR) and northern interior terminals, with improvement expected late in the morning. Otherwise, VFR expected to persist for the majority of the TAF period for mostly all terminals. Breezy S/SW winds along interior terminals will continue this afternoon 10-15 kt and gusting to 20-25 kt, subsiding overnight to 5- 7 kt. Surface flow will shift more northerly late Wednesday morning. KSEA...Scattered showers continue around the terminal this evening. However, any showers that do impact the terminal may briefly reduce ceilings and visibility at times. Models are still in general agreement for convergence zone development to stay north of the terminal tonight. Guidance is hinting at high-end MVFR ceilings between 12z-17z Wednesday morning, with improvement into VFR expected late morning. Otherwise, VFR is favored for the majority of the TAF period. S/SW breezy wind continue this afternoon at 10-15 kt and gusting up to around 20 kt. Winds are expected to subside tonight. Surface winds will shift north/northeasterly late Wednesday morning into the afternoon (6-8 kt). 29/Mazurkiewicz && .MARINE...Westerly surface flow along the coastal waters will shift more northwesterly this evening. A weak push along the Central and East Strait is expected tonight. Sustained wind speeds will be around 15-20 kt, but probabilistic guidance highlights a 60-80 percent chance of wind gusts reaching small craft criteria for a brief period, for which a Small Craft Advisory has been issued. In addition, a Small Craft Advisory remains in effect for the coastal waters and West Strait for high seas 10-11 ft this afternoon. Seas should subside below 10 ft tonight into early Wednesday morning. Weak high pressure will build over the coastal waters on Wednesday and Thursday. The next frontal system looks to arrive on Friday, with high pressure rebuilding over the weekend. Seas 9 to 11 ft this afternoon and will subside late tonight to 7 to 8 ft. Seas look to remain below 10 ft through the rest of the week. 29 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$

910 FXUS66 KPQR 210334 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR Issued by National Weather Service Seattle WA 835 PM PDT Tue May 20 2025 Updated Aviation Discussion... .SYNOPSIS...The recent cool and wet weather will continue through the end of the week and give way to drier weather and above average temperatures as we move into the weekend. && .SHORT TERM...Now through Thursday...Water vapor satellite imagery shows a low amplitude shortwave trough sliding across the Pacific Northwest. This has resulted in scattered, generally light, showers spreading across western Washington and western Oregon today. As 500mb heights build across the region and surface instability decreases this evening, expect showers to gradually decrease in coverage and intensity. In areas that remain clear like the upper Hood River Valley and areas that gradually clear this evening, there is a 50% chance or more for frost in our coldest locations like Odell and Parkdale. The probability for temperatures dropping into the mid 30s is considerably lower (10%-20% chance) for areas like Hillsboro, Battle Ground and across much of the southern Willamette Valley and Cascade Foothill valleys. Brief ridging late tonight into early Wednesday will give way to another shortwave trough sliding across the region late Wednesday into early Thursday. This will bring another round of light precipitation to the region. Ensembles suggest the light rain is most likely to arrive Wednesday evening into Wednesday night with some light precipitation chances lingering into Thursday across mainly the higher terrain. Temperatures look to remain near to slightly below average for the date through Thursday. .LONG TERM...Thursday Night through Tuesday...WPC Clusters suggest the region will be under the influence of a lingering shortwave trough Thursday night into Friday. However, only 20-30% of global ensemble members suggest deep enough troughing over the region to keep some light precipitation continuing mainly over the northern half of the CWA and the higher terrain of the Coast Range and Cascades. Global ensemble membership is generally in agreement that shortwave ridging will build into the Pacific Northwest Saturday into Sunday leading to the area drying out further and temperatures warming to well above average by Sunday. With that said, there is 10-20% of the ensemble guidance that delays shortwave ridging, which keeps Saturday cooler. Uncertainty in the upper level pattern grows early next week. The main uncertainty revolves around how long shortwave ridging persists over the region and when the next shortwave trough slides into the Pacific Northwest. The current forecast is very middle of the road, but know there is ~25% chance temperatures in the 80s will persist into early next week and there is a ~25% chance that temperatures drop into the 60s with beneficial wet weather returning to the Pacific Northwest. && .AVIATION...Weak high pressure begins to build across the region, maintaining VFR conditions throughout the airspace. Inland terminals will see VFR conditions persist through the TAF period, along with northerly to northwesterly winds under 8 kt. Coastal terminals may experience MVFR CIGs before 06Z Wednesday, but expect VFR for the rest of the TAF period. Between 20Z Wednesday and 03Z Thursday, expect gusty northwesterly winds around 10-15 kt with gusts up to 25 kt for coastal terminals. PDX AND APPROACHES...Predominantly VFR conditions through the TAF period with west to northwest winds under 8 kt. ~Hall && .MARINE...A benign onshore flow regime will maintain scattered showers and light to moderate westerly breezes over the coastal waters through tonight. Small Craft Advisories remain in effect through this evening as a mid period period westerly swell keeps seas at or above 10 ft. Seas will subside overnight to 6 to 7 ft by Wednesday morning. Expect relatively calm conditions for the remainder of the week as high pressure yields northerly winds over waters for Wednesday and Thursday, with gusts potentially up to 25 kt later Wednesday afternoon. Onshore flow returns Friday into the weekend. Seas remain in the 5 to 7 ft range through mid week, subsiding below 5 ft by Friday. DH/CB && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Frost Advisory from midnight tonight to 8 AM PDT Wednesday for ORZ121. WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for PZZ210-251>253- 271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland

513 FXUS66 KMFR 202323 AFDMFR Area Forecast Discussion National Weather Service Medford OR 423 PM PDT Tue May 20 2025 ...New Aviation Section... .AVIATION (00Z TAFs)... Expecting a mainly VFR TAF cycle over the next 24 hours. There is one question about low clouds (MVFR) around the coast and Roseburg overnight, but the consensus did not have this coming to fruition tonight given the lack in moisture from most guidance. Will monitor this and update accordingly. Otherwise, high clouds will push into the region tomorrow afternoon with generally light winds through this cycle. -Guerrero && .PREV DISCUSSION... /Issued 315 PM PDT Tue May 20 2025/ DISCUSSION...There may be some showers and thunderstorms on Monday, but this upcoming weekend looks to be a very good time to be outdoors. As weather impacts go, those in our area during the next week look to be relatively minor. They include coastal low clouds (mainly during the night and mornings) Wednesday night through Friday night and Sunday night into Tuesday morning), a slight chance of showers for our northern tier (mainly Coos and northern Douglas counties) late Wednesday night into Thursday morning, weak instability for a slight chance of showers and thunderstorms Friday afternoon and evening for Lake County and the Warner Mountains of northeast Modoc County, above normal temperatures inland for the holiday weekend, and a broad trough on Monday/Memorial Day (lingering on the far east side Tuesday) that could be accompanied by sufficient moisture and instability for a slight chance of showers and late day thunderstorms. A few ensemble members are a little faster with the trough arrival, which could open the door to a few showers near Crater Lake late in the day on Sunday. But, a mere increase in evening clouds is much more likely. A sizable minority of ensemble solutions, and the operational GFS are just a bit slower, which could bring the highest probability of a modest risk of showers or a few thunderstorms for Monday morning, ahead of peak heating. Thus, limiting the extent of activity. First, high pressure will briefly build in on Wednesday with early morning low clouds for southern Douglas County. Warming and drying inland will send temperatures to several degrees above normal. The weak trough Wednesday night into Thursday will send light showers mainly to western Washington and northwest Oregon. A slightly stronger trough will follow for Friday. With both troughs, the most widespread effect will be slight cooling, sending temperatures back to around normal. But, there could be just enough moisture and instability on Friday to produce the aforementioned far east side late day convective activity. The coast will remain typically cool with onshore flow for the weekend. But, highs in the lower 70s to lower 80s will be several degrees above normal inland. We will be paying close attention for better model agreement as we draw closer to Monday and Tuesday. For now, a wash out, or scattered to numerous thunderstorm activity is not at all supported by the data. But, an isolated risk is shown by a sizable minority of ensemble members. AVIATION...20/18Z TAFs...Clouds are diminishing, but VFR ceilings will linger into the afternoon for much of southwest Oregon, including North Bend and Roseburg The typical afternoon and early evening gusty breezes are expected this afternoon into early this evening. IFR low clouds are expected late tonight into early Wednesday morning in the southern portion of Douglas County, near Canyonville. Otherwise, VFR is expected to persist through Wednesday. -Petrucelli/DW MARINE....Updated 200 PM Tuesday, May 20, 2025...North winds have been increasing today and will be strongest south of Cape Blanco. North winds are expected to persist into Wednesday evening, then will diminish Wednesday night as a weak upper trough approaches weakening the thermal trough. Steep west-northwest swell will remain over all waters into early this evening, and then steep seas will remain south of Cape Blanco through Wednesday evening. Light to moderate north winds are expected Wednesday night into the end of the week, but winds and seas are expected to remain below small craft. -Hermansen && .MFR WATCHES/WARNINGS/ADVISORIES... OR...CA...None. PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Wednesday for PZZ350-356-370-376. && $$

859 FXUS66 KEKA 202018 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 1245 PM PDT Tue May 20 2025 .SYNOPSIS...High pressure is expected to build today and Wednesday warming temperatures and clearing skies. Late in the week an upper trough near the area is expected to bring cooler temperatures and more coastal clouds. Warming is expected again for the weekend. && .DISCUSSION...High pressure is building into the area. This is helping to clear skies fairly quickly this morning. This afternoon breezy conditions are expected, especially along the coast. Gusts of 25 to 30 mph are expected over the windiest areas. Tonight some stratus is expected to return, but it looks like it will just be patchy along the Humboldt coast. The Del Norte coast is expected to see slightly more offshore flow keeping the stratus away. The Mendocino coast is also expected to stay more clear. Wednesday is expected to be the warmest day of the week with high pressure overhead. Heat risk is only expected to be minor even in the warmer valleys. Wednesday night and Thursday morning a trough is expected to bring a return of more coastal clouds. A second trough Thursday night into Friday morning is expected to reinforce this first one, likely The precip is generally expected to remain north of the area, but some drizzle is possible, especially overnight. The NBM shows only a 10 percent chance of measurable rain. These troughs also look too dry for any thunderstorms to form, the potential for that lies well to the east of the area. Inland temperatures will be cooler, likely in the 70s. High pressure is expected to build in over the weekend again. This should diminish the marine layer clouds and allow temperatures to warm back close to 90 again. The NBM shows only around a 10 percent chance of high temperatures exceeding 90 degrees. Early next week there is the potential for another trough and possibly some rain. Three of the 4 ensemble clusters show at least a little rain on Monday. However the NBM shows only a 25 percent chance of measurable rain in the north and less than a 15 percent chance of a tenth of an inch. MKK && .AVIATION...Gusty northerly and northwesterly winds and shallow low level turbulence and/or low level speed shear expected tonight, especially along the coast and over the transverse coastal mountains (King Range). Otherwise, mostly clear skies and VFR conditions are expected to prevail for all forecast terminals. Low cloud cover and IFR or LIFR conditions will most likely develop in north coast river valleys overnight under higher stability and warming air aloft. There is a low chance (40%) for MVFR cigs to spread out over KACV mid to late this evening and lower chances for a few hours or less for LIFR in mist and haze at CEC and ACV early Wed morning. DB && .MARINE...Northerly winds and steep waves continued to increase today. HREF probabilistic guidance continues to support peak gusts to 35-40kt in the lee of Cape Mendocino as an expansion fan reaches maximum coverage late this afternoon into the evening hours. Another wind speed max is also forecast to develop late this afternoon and early evening across the northern waters; around and just downwind of Pt St George. Coverage appears minimal to support a gale warning for the northern waters at this time. Steep northerly waves of 6 to 8 ft in the northern waters and 9 to 11 feet in the southern waters on top of a NW swell around 7 to 9 ft will yield combined wave heights of 9 to 11 ft in the northern waters and 11 to 14 ft in the southern waters tonight through Wed AM. Small craft advisories are in effect and inexperienced mariners should avoid going out in these wave conditions. Seas are forecast to remain elevated and hazardous on Wednesday due to this same wave combination, though northerly winds should lay down some. Wind and waves are forecast to ease up toward the end of the week and perhaps into the weekend. It will not take much of a gradient for wind gusts to reach 25-30 kt and for steep wind waves to reach 6 ft for the southern waters and advisories for small craft may still be warranted. A couple of long period swell groups arrive over the weekend; one from the SW and another from the WNW. These swell groups do not appear all that energetic to pose a moderate or extreme risk for sneaker waves at least in our waters over the weekend. It will need to be monitored for possible beach hazards for S and SW faces shores. Otherwise, quieter and fairly tranquil marine conditions are expected over the holiday weekend. DB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Wednesday for PZZ450. Small Craft Advisory until 9 PM PDT Wednesday for PZZ455. Small Craft Advisory until 9 PM PDT Wednesday for PZZ470. Small Craft Advisory until noon PDT today for PZZ475. Gale Warning until 3 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

173 FXUS66 KMTR 210451 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 951 PM PDT Tue May 20 2025 ...New AVIATION... .SYNOPSIS... Issued at 244 PM PDT Tue May 20 2025 Elevated fire weather concerns through Thursday, which will be accompanied with strong and gust northwesterly winds and above normal seasonal temperatures. A pattern change happens late in the week which will bring cooler temperatures for Friday, with temperatures gradually warming over the weekend. && .UPDATE... Issued at 909 PM PDT Tue May 20 2025 Skies remain clear across the region this evening. Dry conditions persist under the upper level ridge, with the Fort Hunter Liggett RAWS site reporting a minimum relative humidity of 8%, while a couple of sites on Highlands Peak near Lucia are currently seeing relative humidity values drop to the single digits as well offshore flow creates a nocturnal drying effect. With even warmer temperatures expected tomorrow (the warmest spots in the interior reaching the low to middle 90s), the elevated fire weather concerns continue tomorrow, especially for the finer fuels such as bushes and grasses. DialH && .SHORT TERM... (This evening through Wednesday) Issued at 244 PM PDT Tue May 20 2025 Key Messages -Elevated fire weather concerns -Breezy north to northwest winds -Above normal seasonal temperatures Upper level dynamics become more lean more zonal with minor signs of weak ridging. At the surface, we remain nestled between low pressure to our east and high pressure to our west leading to a tighter pressure gradient overhead. Breezy north to northwest winds look to persist through the period; however, warmer high temperatures and drier air is on tap for Wednesday. The elevated fire weather concerns will continue for finer fuels such as brush and grass, especially for interior regions. && .LONG TERM... (Wednesday night through next Monday) Issued at 244 PM PDT Tue May 20 2025 Key Messages -Elevated fire weather concerns through Thursday -Breezy north to northwest winds -Cooler temperatures Thursday and Friday, seasonal temperatures return An upper level trough swings through the PacNW on Thursday, which will bring slightly cooler weather to the region. A fairly dry day is still on tap, in terms of RH and no rain, with improving RH overnight. A secondary, and more broad upper level wave approaches the west and Central Coast for Friday, which will bring the coolest temperatures of the week. Upper level ridging looks to quickly fill behind it, leading to the return seasonal temperatures. && .AVIATION... (06Z TAFS) Issued at 951 PM PDT Tue May 20 2025 The marine layer depth to the lower level temperature inversion varies from approx 700 feet to 1400 feet. Drier to much drier air is in the atmospheric mix within the gusty northwest winds along the coast, resulting in VFR. Gusty northwest winds are otherwise resulting in haze/hazy conditions due to sea spray/salt condensation nuclei lofted into the marine layer. The northerly ACV-SFO pressure gradient is 7.4 mb, the onshore gradient SFO-SAC is 2.7 mb. Dry air tonight and Wednesday will have a good chance of continuously mixing into the marine layer i.e. the boundary layer helping to keep VFR going, except the immediate coast may see a patch or two of stratus and/or fog late at night and/or early morning. Otherwise VFR is forecast Wednesday. Gusty west to northwest winds developing Wednesday afternoon and evening. Vicinity of SFO...VFR. West wind 5 to 15 knots tonight and Wednesday morning. West wind with gusts increasing to near 30 knots Wednesday afternoon and evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Moderate to high confidence VFR continues through late evening, then low to moderate confidence VFR forecast late tonight and Wednesday morning. Plenty of dry air is arriving from the north at and above the marine layer temperature inversion, since dry air is molecularly heavier than water vapor the current near term weather pattern may just help extend VFR here along the coastline through late tonight and Wednesday morning. Otherwise VFR Wednesday. West winds 5 to 10 knots tonight and Wednesday morning, increasing to 10 to 20 knots Wednesday afternoon and early evening. && .MARINE... (Tonight through next Monday) Issued at 909 PM PDT Tue May 20 2025 Strong northwesterly winds and hazardous seas will continue over the coastal waters tonight through late week. Westerly winds will become gusty over the bays each afternoon and evening. Winds will diminish and seas will subside gradually into the upcoming weekend. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM to 9 PM PDT Wednesday for Mry Bay. Gale Warning until 3 AM PDT Wednesday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Gale Warning until 9 AM PDT Wednesday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Gale Warning until 9 PM PDT Wednesday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...KR LONG TERM....KR AVIATION...Canepa MARINE...Canepa Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea

525 FXUS66 KOTX 210539 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1039 PM PDT Tue May 20 2025 .KEY MESSAGES... - A 25% chance for afternoon thunderstorms through Tuesday evening in the northern mountains. - Patchy frost for colder pockets in northern mountain valleys Tuesday night into Wednesday morning. - Chance of rain showers increased for Thursday - Mild with showers and isolated thunderstorms start to the holiday weekend followed by warm and dry conditions into Memorial Day. && .SYNOPSIS... Showers will continue over the northern mountains and Idaho Panhandle through Wednesday, along with a chance of thunderstorms through Tuesday evening. Patchy frost is expected in colder pockets of the northern mountain valleys for Wednesday morning. Then temperatures see a gradual warming trend into the holiday weekend. Thursday through Saturday remains unsettled with showers at times. Drier and warmer Sunday into Memorial Day with temperatures warming into the 80s. && .DISCUSSION... Today through Thursday morning: As the low pressure system currently sitting over top of the forecast area slowly weakens and moves out of the area, rain showers will continue. These showers will mostly be confined to the mountain areas due to orographic lift. Rain totals will overall be less than 0.1 inches except for localized areas within the mountains. Winds through the afternoon will continue to be breezy across most of the area, with gusts 25-30 mph anticipated. Lift provided by the low will contribute to a general chance (25 percent) for thunderstorms throughout far northeastern Washington and the northern Idaho Panhandle. Strongest thunderstorms are anticipated through around 8pm this evening. Clearing tonight will allow temperatures to be chilly, with some frost chances. In particular, the NBM shows percentages of seeing 36 degrees or below over 60 percent for northeastern locations such as Republic and Colville. As such, a Frost Advisory has been issued for the Northern Mountains and Okanogan Highlands from 2-7am tomorrow morning. Tomorrow, both high and low temperatures are expected to increase to closer to normal, so frost should no longer be a risk. /AS Thursday through Tuesday: A mid level short wave tracks into the region on Thursday bringing another round of showers to the region. The ensembles are currently struggling with the coverage of precipitation, with the GEFS the wettest with amounts of 0.10-0.20" across much of Eastern WA/N Idaho, while the Canadian ensemble is the driest with amounts less than 0.10" over SE Washington into the south ID Panhandle. The EC Ensemble is a compromoise between the wet GEFS and drier Canadian. Given the high PWAT`s near 125% of normal, and the short wave coming through during peak heating, the forecast is leaning towards a compromise of the GFS/EC Ensemble solutions. Thus POP`s were raised above the NBM. This short wave moves out Thursday Night bringing about a warming and drying trend through the Memorial Day weekend. Some residual showers are expected Friday and Saturday in the mountains but will be isolated/scattered in nature. The next trough sets up off the coast placing the Inland NW in a milder southerly flow. This will allow high temperatures to warm into the 70s and 80s by Sunday and Monday. Then the offshore trough begins to push the ridge east late Monday into Tuesday. The details become more uncertain this far out, with POP`s nudging upward and temperatures down heading into Tuesday. JW && .AVIATION... 06Z TAFS: VFR conditions are forecast for all TAF sites through 06z Thursday. Winds will also be on the decrease tonight as pressure gradients weaken and the lower atmosphere stabilizes. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in VFR conditions through the TAF period. ----------------------- Confidence descriptors: Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance For additional probabilistic information for NWS Spokane airports, please refer to the Aviation Dashboard on our webpage: https:/www.weather.gov/otx/avndashboard && .Preliminary Point Temps/PoPs... Spokane 38 63 43 60 43 67 / 10 10 0 50 20 10 Coeur d`Alene 37 62 41 60 41 68 / 20 10 0 60 20 20 Pullman 37 60 43 56 40 65 / 10 0 10 60 20 10 Lewiston 44 68 50 64 47 73 / 10 0 10 60 20 10 Colville 32 62 36 64 37 67 / 50 50 10 30 10 20 Sandpoint 39 61 40 61 43 68 / 30 40 0 50 20 20 Kellogg 39 58 43 57 43 65 / 20 30 10 70 30 20 Moses Lake 39 68 47 71 44 75 / 0 0 10 20 0 10 Wenatchee 42 68 50 71 47 72 / 0 0 0 20 10 10 Omak 39 68 42 71 43 73 / 10 10 0 10 10 20 && .OTX WATCHES/WARNINGS/ADVISORIES... WA...Frost Advisory from 2 AM to 7 AM PDT Wednesday for Northeast Mountains-Okanogan Highlands. ID...None. && $$

836 FXUS66 KPDT 210523 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1023 PM PDT Tue May 20 2025 Updated Aviation Discussion .AVIATION...06Z TAFs...VFR conditions to prevail through the period. CIGs will clear or become few AOA 25kft through the the overnight hours, becoming BKN and lowering to around 15kft tomorrow. Light winds have also developed this evening, and are expected to remain light, 12kts or less, and diurnally driven through the period. Lawhorn/82 && .PREV DISCUSSION... /issued 446 PM PDT Tue May 20 2025/ .SHORT TERM...Tonight through Thursday Night...Last night`s shortwave has moved off to the east and a zonal westerly flow has set up over the Pacific Northwest today. An upslope flow into the mountains will keep a slight chance of very light mountain showers into early this evening but overnight and tomorrow look to be dry. Breezy west winds through the Cascade gaps will continue from at 15 to 20 mph with gusts to 30 mph and the west to northwest at 10 to 15 mph with gusts of 20 to 25 mph in the Columbia Basin through early evening then decrease overnight. Despite an approaching shortwave, pressure gradients are much lighter on Wednesday and winds will turn northerly at 10 mph or less. The zonal flow will warm temperatures 6 to 10 degrees over most of the area but the northerly winds will only allow a couple of degrees of warming in the Columbia Basin. Highs will be in mid 60s to lower 70s with upper 50s to mid 60s in the mountains. Wednesday night, models continue to show a fast moving wave arriving in the evening in central Oregon then progressing through the eastern mountains overnight before exiting the area Thursday afternoon. The wave looks a little weaker than on previous model runs but should still generate light rain showers in central Oregon initially then over the eastern mountains. Rainfall amounts in the above mentioned areas will be a tenth of an inch or less. The Washington portion of the area will see little if any rain. NBM probabilities show a 25 to 50 percent chance of getting a tenth of an inch of rain in the eastern mountains. The NBM also shows enough instability Thursday afternoon as the wave moves over the eastern portions of the area to put a 15-20 percent chance of thunderstorms over the Blue Mountains and Wallowa County though any cells that develop would be fairly weak. With the wave crossing the area and heavier cloud cover, temperatures in the southern half of the area will drop 3 to 5 degrees while further north in the Columbia Basin, temperatures will see little change from Wednesday. In the wake of the departing wave, models set up a shallow trough along the coast with a southwest flow over our area Thursday night. What few showers that linger will end in the early evening. Perry/83 .LONG TERM...Friday through Tuesday... Key Messages... - Scattered mountains showers and low thunderstorm chances (up to 20%) in the far eastern mountains and Wallowa Friday with dry conditions this weekend, - Above average highs by as much as 10-15 degrees Sunday-Tuesday with the warmest conditions Sunday/Monday, and - Unsettled weather with best chances (20-50%) in the Cascades and eastern mountains. The large scale pattern early Friday will feature a quasi-zonal mid- level flow with an embedded shortwave trough crossing the region. This will be followed by the amplification of an upper-level trough in the eastern North Pacific and an upper ridge downstream across the Northern Intermountain West this weekend. Initially, guidance is in fair agreement with low spread seen amongst ensemble guidance until Sunday when the upper trough begins to de-amplify. Thereafter the upper-level ridge will progress to be over the Rockies extending north into Saskatchewan Monday-Tuesday with the area under southwest flow. Of which, an embedded disturbance or two emerging out of the eastern North Pacific is anticipated to promote low chances (20-50%) in afternoon Monday/Tuesday as the upper trough de-amplifies. On Friday, the convective parameter space is not strongly favorable for thunderstorm chances between the marginal moisture in the lower troposphere and surface, as seen in proximity soundings, in tandem with 6.5-7 C/km mid-level lapse rates. This expectations matches what are seeing when it comes to guidance thunderstorm probs with chances as high as 20% in eastern Grant and Wallowa counties. Otherwise, the area will see a warming trend begin Friday that peaks Sunday/Monday as a warmer air mass takes hold. While there is some disagreement late Sunday, the sensible weather impacts are isolated and confined to the upper Cascades. Ensemble clustering shows a chance (1 out of 5) where a faster/eastward solution with this trough will promote a slight increase in mountain showers on Sunday. Looking into early next week, guidance is largely supportive of the upper ridge shifting and building progressing eastward. As noted in initial forecasts, clustering scenarios showed the potential for the upper ridge to linger and be displaced west longer. Thus promoting potentially warmer temps than currently forecast on Monday and Tuesday. Of which, clustering dprog/dt shows this outcome, lingering ridge, becoming more unlikely (compared to past runs Monday. That said, Monday boast similar chances for 90s or higher in the lower Basin (10-20%) compared to Sunday; Tuesday has these chances linger as well (~10%). Meantime, an ejecting disturbance from the upper trough will promote lingering chances in the Cascades and in the afternoon/evening mountains, 10-50%, Monday and Tuesday. Lowest chances will be in north central OR and the western/central Lower Basin where dry conditions are more likely than not to prevail. && .PRELIMINARY POINT TEMPS/POPS... PDT 41 69 47 67 / 0 0 40 50 ALW 45 68 49 66 / 0 0 30 50 PSC 42 71 48 72 / 0 0 20 30 YKM 39 70 50 71 / 0 0 10 20 HRI 42 71 49 72 / 0 0 30 40 ELN 39 68 46 69 / 0 0 10 20 RDM 32 70 41 65 / 0 0 40 20 LGD 34 66 44 62 / 0 0 40 60 GCD 34 70 44 64 / 0 0 50 50 DLS 42 72 50 70 / 0 0 30 30 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...83 LONG TERM....80 AVIATION...82

150 FXUS65 KREV 202127 AFDREV Area Forecast Discussion National Weather Service Reno NV 227 PM PDT Tue May 20 2025 .KEY MESSAGES... * Warm and dry weather prevails through midweek with streamflows running fast and very cold this week. * Gusty winds return Thursday and Friday, resulting in travel, recreation, and fire weather impacts. * The holiday weekend continues to lean towards a warm and dry scenario, although showers or a stray storm cannot be ruled out. && .DISCUSSION... Very warm and dry weather prevails through the week with daytime highs in the 70s and 80s areawide. Residual high Sierra snowpack will continue to melt amid our June-like warmth, resulting in regional streamflows running fast and very cold. A weak trough tandem will increase winds Thursday and Friday, inducing travel, recreation, and fire weather impacts (see Fire Weather discussion below) leading up the holiday weekend. If you plan on traveling for the long weekend, be prepared for bumpy flights into/out of regional airports, difficult driving conditions along N-S oriented roadways (e.g., I-580 near Washoe Valley, US-95 near Walker Lake, US-395 near Honey Lake), and reduced visibilities due to blowing dust across the Basin and Range. Hazardous boating conditions are also likely on area lakes, including Lake Tahoe and Pyramid Lake Thursday and Friday afternoons. A few showers or stray thunderstorm will be possible near the Oregon Thursday and Friday afternoon with dry weather prevailing elsewhere. Very warm or, dare I say, hot temperatures remain favored for the holiday weekend, especially Sunday and Monday as high pressure overspreads the region. As such, area creeks and streams will look very enticing to cool off in, but remember that the prolonged warmth will mean streamflows will be running fast and very cold so be sure to avoid jumping in! -Salas && .AVIATION... Widespread VFR conditions and light afternoon breezes prevail through Wednesday. Gusty winds return Thursday, increasing the potential for LLWS and mountain wave turbulence impacts during a busier travel period ahead of the holiday weekend. -Salas && .FIRE WEATHER... A multi-hour period of elevated to critical fire weather conditions is likely Thursday and Friday afternoon across much of western Nevada where west to southwest gusts of 30-40 mph overspreads afternoon RH`s of 7-15%. Very warm and dry weather continues into the weekend, but winds are expected to be lighter. While a lack of prominent fuel intel will preclude the issuance of any products, a report from the Great Basin GACC did reveal that we remain in green-up with curing cheatgrass. -Salas && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$

037 FXUS66 KSTO 201950 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA Issued by National Weather Service Reno NV 1250 PM PDT Tue May 20 2025 .Discussion... .Synopsis... Warming trend and areas of Moderate HeatRisk in the Valley through the middle of the week as ridging aloft briefly settles in. Temperatures then expected to fluctuate between near and slightly above normal late week into the weekend as a more progressive pattern sets up aloft. Precipitation chances less than 10 percent at this time, but periods of breezy to briefly gusty winds possible. Elevated fire weather conditions expected to persist through the end of the week. && .Key Messages... * Today - Wednesday: -Above normal high temperatures in the 80s to low 90s today,with Valley highs into the mid 90s and areas of Moderate HeatRisk on Wednesday. -Very dry conditions and diurnally breezy winds expected as elevated fire weather conditions persist. * Thursday - Sunday: -Quick moving, dry shortwaves bring periods of breezy to briefly gusty onshore winds Thursday and Friday. -Probability of South-Southwest Wind Gusts > 30 mph: --Thursday: 60-90%, highest across Delta and vicinity --Friday: 30-60%, highest across Delta and vicinity -Despite marginal improvements in RH from onshore flow, elevated fire weather conditions likely continue, especially during periods of strongest winds as systems move through. -Fluctuating temperatures expected, with primarily areas of Minor HeatRisk through the Valley expected. .Changes from previous forecast... -Slight increase in wind magnitude, but also attendant RH recovery with moisture advection Thursday & Friday. && .AVIATION... VFR conditions prevail across interior northern California over the next 24 hours. Northerly wind gusts of up to 15 to 20 knots at times across the Central Valley and Delta through 21Z-00Z Wednesday, then winds become more westerly. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$

538 FXUS65 KMSO 201856 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1256 PM MDT Tue May 20 2025 .DISCUSSION... KEY MESSAGES: - Alternating between cool/showery and mostly dry with an active weather pattern this week - Increased risk of frost tomorrow morning - Warm and dry likely early next week A weak disturbance embedded in a zonal flow will continue to produce scattered rain showers, along with a 20 percent probability of thunderstorms into the evening hours. The shortwave will also help mix down gusty westerly winds, with a 75 percent probability that gusts will reach or slightly exceed 25 mph through sunset this evening across the Northern Rockies. Expect choppy conditions on area lakes, especially Flathead Lake. A transitory ridge will move into the region tonight and into Wednesday, resulting in a temporary decrease in shower activity. The exception will be northwest Montana, where a few showers may linger. Temperatures are expected to dip into the low to mid-30s in many of the valleys again on Wednesday morning, bringing an increased risk of frostespecially in areas where skies remain clear overnight. Another disturbance will impact the Northern Rockies on Thursday, once again bringing widespread showers, with isolated thunderstorms mainly south of I-90. Snow levels during this event will range between 6,500 and 8,000 feet. A secondary disturbance is expected to move through the region from Friday into Saturday, keeping showers lingering over the Northern Rockies. Nearly all long-range ensemble members are now in agreement that a ridge of high pressure will build over the Northern Rockies as early as Sunday and remain in place through the middle of next week. This will lead to a warming and drying trend, with afternoon temperatures ranging 10 to 15 degrees above normal by Sunday or Monday. && .AVIATION...A weak disturbance embedded in a zonal flow will continue to produce scattered rain showers and a 20 percent probability of thunderstorms into the evening hours across the Northern Rockies. The shortwave will also help mix down gusty westerly winds, with a 75 percent probability that gusts will reach 20 to 25 knots from 20/2000Z through sunset this evening. A drier period is anticipated tonight and Wednesday under weak ridging, with VFR conditions expected across much of the Northern Rockies. The exception may be northwest Montana, where a few showers and mountain obscurations could continue. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$

165 FXUS65 KBOI 210242 AFDBOI Area Forecast Discussion National Weather Service Boise ID 842 PM MDT Tue May 20 2025 .DISCUSSION...No updates to the forecast. Skies will clear tonight and winds will weaken. Wednesday will be mostly dry as we continue the warming trend under an upper level ridge. Thursday through Saturday we are still expected a slight chance of showers and storms across the northern portions of our area, but the weak appears fairly weak, so a significant degree of uncertainty still exists about peak storm potential. The long term forecast appears very warm, about 10-20 degrees above normal with highs approaching 90 degrees in the Valley on Monday. && .AVIATION...VFR and clearing skies overnight. Surface winds: W-NW at 10 to 15 kt with gusts to 20 kt, becoming light and variable overnight. Winds aloft at 10kft MSL: W 15-25 kt. KBOI...VFR. NW winds 5-10 kts this evening before becoming light and variable overnight. && .PREV DISCUSSION... SHORT TERM...Tonight through Thursday night...Northwest flow over the region today will be replaced by weak upper ridging on Wednesday. This will bring warmer temperatures and lighter winds under a more stable air mass. The ridge won`t be in place long, as a trough pushes into the Pac NW coast late Wednesday. Increasing clouds Wednesday evening will trend into showers late Wednesday night and Thursday as the shortwave lifts from s-central Oregon into central Idaho. It`s an energetic wave in model guidance with a compact jet max accompanying it. Have introduced thunderstorms mostly across Baker County and mtns of w-central Idaho on Thursday. Current guidance shows the best overlap of thunderstorm ingredients across the northern Boise mtns and w-central Idaho mtns. A frontal passage will bring breezy W-NW winds with gusts of 25 to 40 MPH across open and elevated terrain Thursday afternoon/evening. Conditions quickly stabilize Thursday night as the wave is quick to exit the area. Temperatures trend warmer through Thursday which will see near normal highs. LONG TERM...Friday through Tuesday...Another upper-level shortwave trough will be moving in Friday afternoon into evening. In part due to its favorable timing during peak daytime heating, showers and thunderstorms and forecast on Friday. The NAM is by far the most aggressive with CAPE values around 700 J/kg, while the GFS and ECMWF keep CAPE values generally below 500 J/kg. Shear values largely depend on how the shortwave orients, but values of 30 kt are likely with 35-40 kt being the extreme. The coverage of this event is still up in the air, however the maximum of thunderstorm potential exists along the southern border of OR/NV and ID/NV. Snow levels will be around 7500-9000 ft MSL during this event. Starting Saturday and persisting until Monday, a strong longwave upper-level ridge will build over the Desert Southwest through the Northern Rockies. This will begin a gradual increase of temperatures through the weekend and into Memorial Day. On Monday into Tuesday, the GFS, ECMWF, and Canadian all hint at a glancing blow from an upper-level trough that rides the ridge north away from our area. There is considerable difference between solutions late Monday into Tuesday between the ECMWF and GFS/Canadian, thus this will be the end of the discussion. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise DISCUSSION...JM AVIATION.....JM SHORT TERM...DG LONG TERM....CH

784 FXUS65 KLKN 201915 AFDLKN Area Forecast Discussion National Weather Service Elko NV 1215 PM PDT Tue May 20 2025 .KEY MESSAGES... * A warming trend is expected through Friday. * Mostly dry weather for the next several days. * Breezy to locally windy conditions possible Thursday afternoon. && .DISCUSSION... (This afternoon through Wednesday) Issued at 751 AM PDT Tue May 20 2025 WEATHER PATTERN OVERVIEW: A weak shortwave will continue moving through far northern Nevada this afternoon. Not much is being seen on radar at this time however. The activity will wane during the evening hours. The rest of the area will see mainly dry conditions tonight with lows in the 30s and 40s. Slowly rising heights tomorrow will result dry conditions with warming temperatures in the 70s to low 80s. Winds will remain light. Dry weather will remain for Wednesday night with lows in the 40s and 50s. Modest shortwave skirts northern Nevada Thursday. Depending on how far south and whether this feature passes thru portion of far northern Nevada, a few light rain showers may develop in the afternoon with cumulus buildups and virga the more likely fare. Weak instability associated with the shortwave will help produce a dry thunderstorm or two as well, mainly in and near the Jarbidge Wilderness. Dry conditions elsewhere under partly cloudy to mostly sunny/clear skies. Westerly breezes will also be present across the forecast area with gusts 30 to 35 mph. Winds ease overnight. Daytime high temperatures reside in the low 70s to low 80s in the north with warmer readings in the low to mid 80s across portions of northern Nye County. Stronger shortwave trof passes form the west on Friday. Southwest flow aloft will develop during the afternoon. Slightly better instability will bring isolated rain showers to northern Nevada in the afternoon and evening with greater areal coverage. A dry thunderstorm or two is again possible. Shortwave continues to exit to the east Saturday morning with light isolated showers again present during the day. Significant rainfall accumulation is not anticipated. Otherwise, other locations are expected to see a mix of sun and clouds. Breezes again present with gusts to 25 to 35 mph, with the higher end gusts located across central Nevada. Long wave trof amplifies offshore Sunday and early next week with an upper level ridge and high pressure building over the western U.S. Weather will be fair and warm with afternoon breezes and temperatures widespread in the 80s. FORECAST CONFIDENCE & DEVIATIONS: Current model agreement is good and did not deviate from current NBM runs. && .AVIATION... (00Z TAFS) VFR conditions expected at all terminals through the next 24 hours. Breezes will ease this evening with light to calm winds tonight. Fair weather conditions across the forecast area Wednesday. && .FIRE WEATHER...A weak disturbance will be moving across portions of extreme northeast Nevada this afternoon and evening. Sufficient moisture and instability exists for isolated showers in zones 438/469/470 this afternoon. Otherwise, the weather will continue to remain dry with seasonable temperatures. Look for dry conditions Wednesday as heights rise slightly, resulting in slightly warmer conditions with minimum relative humidity values in the single digit to low teen range in central Nevada, with values generally above 20 percent in the north. Breezes to 20 mph will develop in the afternoon especially in the central zones. There is a possibility of isolated showers and thunderstorms across zones 438/469/470 Thursday afternoon with much of the activity mainly in southern Idaho. && .LKN WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...86/92 AVIATION...92 FIRE WEATHER...86