000 FXUS66 KSEW 091649 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 845 AM PST Mon Dec 9 2019 .SYNOPSIS...Low clouds cover much of the lowlands this morning but should break up in the afternoon. A weak front will move through Western Washington Tuesday afternoon and evening. Stronger weather systems will give Western Washington wet and breezy weather Wednesday night through Friday. && .SHORT TERM /TODAY THROUGH WEDNESDAY/...Low clouds and some fog patches cover the lowlands this morning--and then a little sunshine is likely for the afternoon. A transitory upper ridge axis just offshore will shift through the region tonight and Tuesday as it is dented by a weakening front. The front will spread some rain to the coast by the middle of the day and into the I-5 corridor by late afternoon. Ridging pokes back up over Western Washington behind the system Tuesday night and Wednesday morning ahead of the next stronger frontal system that will arrive late in the day Wed. .LONG TERM /THURSDAY THROUGH SUNDAY/...A more active pattern is likely for the second half of the week with wet breezy weather Wednesday night through Friday. An upper trough in the northeast Pacific Wed-Fri will weaken, progress east, and a shortwave on Saturday will mainly affect northern California--leaving Western Washington on the cool showery side of the westerlies for a day. As another trough develops in the north Pacific early next week, downstream ridging occurs over the Pacific Northwest starting on Sunday. && .AVIATION...An upper level ridge centered offshore will move inland tonight. Light flow in the lower levels will persist through Tuesday morning. The airmass is moist and stable, with a drying trend expected this afternoon. Mixed bag of conditions this morning, with ceilings below 1000 feet and visibility 1-3sm in fog. Isolated visibilities 1/2sm or less. Cloud tops 1000-1500 feet. Mid level deck dissipating with ridge moving overhead this morning which will allow the sun to work on the shallow fog layer. Low clouds should scatter out near midday. High level clouds will increase tonight ahead of the next system on Tuesday, but not in time to prevent some areas of fog from reforming around midnight tonight. KSEA...Current ceilings below 500 feet with visibility 1-3sm in fog and low clouds. Improving trend from 17z-21z with clouds scattering out by the early afternoon hours. Fog could reform after midnight, dropping visibilities down again. Light northeasterly winds through tonight 2-6 knots. Felton/Borth && .MARINE...Weak high pressure will remain over the area today. A weakening front will then move through the area on Tuesday, bringing small craft advisory strength easterlies to the western Strait of Juan de Fuca and small craft strength southeasterlies to the Coastal Waters. A stronger frontal system will then move through the area Wednesday and Thursday. Gales are possible for the Coastal Waters with this system Wednesday night. In addition, west swell will build to around 15 feet Wednesday night and Thursday. && .HYDROLOGY...River flooding is unlikely for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 6 PM this evening to 2 PM PST Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory from midnight tonight to 2 PM PST Tuesday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory from 2 AM to 2 PM PST Tuesday for West Entrance U.S. Waters Strait Of Juan De Fuca. && $$ www.weather.gov/seattle

794 FXUS66 KPQR 091634 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 834 AM PST Mon Dec 9 2019 Short term discussion updated. .SYNOPSIS...Dry today, but wet pattern resumes Tue, as a series of front line up to push into the Pac NW this week. More rain arrives later Wed, with rather wet Thu on tap. The wet unsettled weather continuing into next weekend, though there is some hints of drying later next weekend. Snow levels stay at or above pass levels. && .SHORT TERM...Today through Wednesday...Visibility in fog has generally improved to above 1/4 mile, so cancelled Dense Fog Advisory. Fog will still be present in some spots, but expect the overall improvement trend to continue. The remainder of the short term discussion follows. Bowen Brief ridging over the region today, with dry weather on tap. However, still have considerable low clouds across much the region, with areas of morning fog. No fog advisories as visibility in the fog will generally be a half to 2 miles. Any dense fog will be rather spotty and localized. However, A different case for the Willamette Valley from Wilsonville southward through Eugene, as will see widespread fog with visibility below 1 mile. Will put up Dense Fog Advisory for Central and South WIllamette Valley, for areas of dense fog. But, will not issue any dense fog advisory for the interior from Portland northward, as the dense fog for those areas would be patchy and localized. Air mass will remain quite saturated for this morning, so any fog will be slow to thin. Otherwise, mix of sun and clouds on top above the fog, with mild temperatures expected again today. Next front will approach the region later tonight, with increasing mid and high clouds. Thicker clouds do not arrive until later tonight, so will be plenty of time for temperatures to cool and air mass to saturate, with areas of fog for the interior. Spotty rain should spread the coast late tonight, with rain spreading inland after daybreak Tue. System is getting stretched apart, so support for any decent rainfall is limited. Will keep PoPs somewhat elevated, but rainfall amounts will be on the lighter side. Remains of the front will gradually shift inland during the day, with rain becoming more spotty in nature by mid to late afternoon. Brief break for Tue night into early Wed, as weak ridge passes over the region. But, the next front will be fast approaching from the west on Wed. At moment, have decided to go with a 60-40 blend of the GFS/NAM and ECMWF runs, which have timing differences with arrival of the rain. But, all seem to agree that rain will be increasing over the region late Wed afternoon into the evening. Will trend forecasts in that direction. /Rockey .LONG TERM...Wednesday night through Sunday...A front will move into northwest Oregon and southwest Washington on Thursday bringing ample precipitation to the area. While it will predominately fall as rain, snow is expected along the Cascades. This front is well ahead of a broad low pressure system with the low centered over the northern Gulf of Alaska. As the low moves eastward, zonal flow will take over. This generally westerly flow will usher in colder air from the North Pacific which will cause temperatures to begin to fall slightly on Friday. Snow levels will follow suit dropping to near 3,500 ft Friday night. A weak shortwave and continuous cold air flow will bring low temperatures to the mid 30s through the Willamette Vally, and snow levels below 2,000 ft on Sunday. At this point, models are in decent agreement with the overall synoptic pattern, but there is quite a bit of spread in the mesoscale features. The spread in solutions is leading to less confidence in the output after Friday. /Muessle && .AVIATION...Conditions generally IFR to LIFR early this morning with more LIFR south of KUAO and better conditions to the north. From about KUAO north there is a cloud layer around 1000-1500 ft that has hindering fog from becoming dense. Model consensus shows significant improvement around 18Z and most areas becoming VFR around 21Z. Continued stable conditions this evening will bring a return of IFR conditions after 08Z. However with the upper ridge shifting east of the Cascades late tonight and early Tue, increasing clouds and southwest flow aloft will likely affect fog development. Also increasing east wind from the Gorge will likely keep KTTD and KPDX VFR. KPDX AND APPROACHES...Will see IFR/LIFR conditions in the area improve 17-18Z with VFR likely shortly after. Increasing east wind will likely keep the area VFR through tonight, particularly KPDX eastward. /mh && .MARINE...Another quiet day across the marine waters with light offshore flow with seas around 5 to 6 ft at 11 seconds. But this will change as a series of front will affect the waters through mid week. By Tue morning the first front to bring southerly wind gusts 25 kt, but then quickly fall back to the 15 kt. Seas will temporarily build to near 11 ft Tue afternoon. Zonal westerly flow around a broad low pressure over the north Pacific is expected to increase seas to near 15 ft by Thu. While the low is not expected to advance towards the waters, a shortwave embedded in the flow around the low will. At this time, confidence in this system is not high as models are depicting seas a bit higher than what would generally be expected with this system. It is possible that seas will be increased as the event comes closer./mh -Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until noon Tuesday for much of the interior below 1500 feet elevation. WA...Air Stagnation Advisory until noon Tuesday for much of interior southwest Washington below 1500 feet elevation. PZ...None. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. This area is commonly referred to as the forecast area.

000 FXUS66 KMFR 091149 AFDMFR Area Forecast Discussion National Weather Service Medford OR 349 AM PST Mon Dec 9 2019 .DISCUSSION...The dense fog from earlier in the night has lifted in part due to the band of high cirrus. Although visibilities are still reduced in many locations, the dense fog has not come back as anticipated. Thus, have cancelled the dense fog advisory. The fog may become dense once again around sunrise, but confidence is too low to continue the currently unneeded advisory. -Schaaf && .PREV DISCUSSION... /Issued 240 AM PST Mon Dec 9 2019/ DISCUSSION...Satellite imagery is showing fog across most of the valleys in southern Oregon and northern California. A band of higher cirrus clouds are also traversing the area which has disrupted the fog from becoming extremely dense for the moment. Still the drive into work provided some patches of extremely dense fog where visibilities in the Rogue Valley were well less than a quarter of a mile. As a result, have issued a dense fog advisory for many of the West Side Valleys in Oregon through this morning. Once this band of cirrus moves away, the fog will reform pretty quickly and will become dense once again. This is to be expected as our ridge of high pressure continues to build. This means that mixing heights will be meager under the inversion with limited transport winds. If this were to last more than 24-36 hours, an air stagnation advisory may have been issued. This pattern will continue into Monday night with another round of fog and freezing fog over most of our area valleys. Then, on Tuesday, a weak front will move through the area. This front looks like it could bring some light precipitation to areas west of the Cascades by Tuesday afternoon and evening with more widespread (East Side) precipitation occurring Tuesday evening and overnight into Wednesday morning. Snow levels will be around 6000 feet west of the Cascades and 4500 feet east of the Cascades. Come Wednesday, the snow levels will moderate out closer to the 5000 foot level. The big thing this front will do is break down the ridge into more zonal (west to east, upper level flow) flow. Snow levels will rise to 5500 to 6500 feet by Thursday as the next system comes in. This system will also bring considerably more precipitation to southern Oregon and northern California. Still this system looks rather typical for this time of year with the exception of high snow levels (6000 feet). After the front passes through on Friday, the precipitation will become showery in nature as the snow levels drop to around 4000 feet by Friday night. The next part of the forecast marks a relative change from previous shifts. Ensemble forecasts as well as the deterministic models are showing signs that the next low could dip farther south into northern California (south of Siskiyou and Modoc Counties) leaving us mainly dry. Have trended toward the drier solution as seen in the National Blend of Models, and if this trend continues, we could see a drier weekend. For now, am keeping the showers in the forecast on Saturday and drying things out for Sunday. Snow levels for will also continue to drop at this time (as will the resulting temperatures for our area) to around 2500 feet or so by Saturday night into Sunday as the precipitation comes to an end. It is too far into the future to determine what impacts these systems will hold, but it will be worth keeping an eye on the forecast for any more drastic changes like we saw tonight. That being said, taking a sneak peak into the far extended forecast shows another quick ridge building in early next week before a front moves to more zonal flow and more systems coming in. We could continue this relatively active pattern up through the end of the year, (brief ridges with systems breaking them down every couple of days) but we will have to be patient to see how things actually shake out. -Schaaf AVIATION...For the 09/12Z TAFs...The air mass will further stabilize early this morning with LIFR/IFR conditions expanding and becoming common in valleys. The low clouds and fog are likely to linger well into the morning with the low ceilings and visibilities lingering into the early afternoon in areas. The extent of VFR will be at a maximum in the late afternoon, then low clouds and fog are expected to redevelop in west side valleys this evening. -DW MARINE...Updated 230 AM PST Monday, 9 December 2019...Weak high pressure will persist over the waters today with light winds into this evening. Winds will increase and seas will become steep Tuesday morning ahead of a cold front. There is still variation among model solutions leading to some uncertainty in whether wind speeds with the front on Tuesday will quite reach advisory strength. But, we are highly confident that the combination of gusty south winds and west swell will create overall conditions that are hazardous to small craft. The front will be the start of a new series of disturbances with slight, brief improvement in conditions early Wednesday, then steep seas likely continuing into the weekend. This includes a high to very high and steep to very steep long period west swell Thursday into Friday. With a consistent model forecast during the past few days, confidence is increasing that this westerly swell will become large enough (at least 15 feet at 15 seconds) to impact bar crossings and crab pots. DW/Keene && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. Pacific Coastal Waters...Small Craft Advisory from 4 AM to 10 PM PST Tuesday for PZZ350-356-370-376. $$

000 FXUS66 KEKA 091305 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 505 AM PST Mon Dec 9 2019 .SYNOPSIS...Morning low clouds and areas of fog will give way to sunshine today. A weak front will bring light rain to northwest California Tuesday, followed by a brief period of high pressure on Wednesday, before an extended bout of wet weather begins on Wednesday night. && .DISCUSSION...Fairly extensive low clouds and fog have enveloped almost all valleys in northwest California, and some marine layer cloudiness is covering portions of the coast this morning as well. Meanwhile, some weak offshore flow is helping to keep much of the Del Norte and Mendocino coast clearer. Expect most of these clouds and fog to lift and scatter by midday. However, with such a strong inversion under a highly amplified ridge of high pressure, the clouds may linger into the afternoon in some of the valleys and along the beaches as well. Either way, high pressure will provide stable and dry weather for at least today, with likely the sunniest day of the week for most locations, before the inevitable return to wet weather begins on Tuesday. For Tuesday, a weakening surface cold front and `split` upper level trough will approach from the west. Model guidance has consistently depicted a period of light rain through between the midday and evening hours. Rainfall amounts will likely range from a tenth of an inch to locally up to a half inch with this system. A southerly breeze will develop over the mountain ridges, but otherwise expect light winds today to continue during the passage of this system, and right through Wednesday. In the wake of the weak front, high pressure will likely rebuild across California on Wednesday both at the surface and aloft. This should allow for a mainly dry and mild day. More wet weather will head our way for much of the period from Wednesday night through Saturday, with a series of fronts passing by. Between an intense upper- level low in the Gulf of Alaska and a strong ridge of high pressure off the coast of southern California, deep and moist westerly flow will support this wet period. That said, none of the individual systems passing through look particularly strong for northwest California. Rainfall may end up totaling more than a few inches over the mountains of northern Humboldt and Del Norte, with lesser amounts to the south. Strong winds are not expected, and snow levels will remain high until colder air starts to settle in from the north around Friday night. Even then, it appears doubtful that much precipitation is left around by the time the snow levels drop to our mountain passes later in the weekend. /AAD && .AVIATION..Intermittent IFR ceilings have plagued Northwestern California overnight, although light offshores have cleared the Del Norte coastline early this morning. Farther south, IFR ceilings currently still in place are expected to dissolve around mid- morning as daytime heating mixes the lower atmosphere. Low clouds will likely return this evening, but may be short lived as high clouds from an approaching front move overhead late tonight and inhibit further development. /TDJ && .MARINE...Light northerlies offshore this morning continue to diminish today and shift southerly tonight as a front approaches from the west. These look to increase to marginal SCY levels Tuesday afternoon, generating short period southerly seas around 6 ft at 6 seconds. Meanwhile, a W swell is expected to fill in on Tuesday, for combined seas of 9 to 11 ft by early Tuesday afternoon across the outer waters. Thus have lifted a small craft advisory for the outer waters in response for Tuesday. Southerly winds drop below advisory levels for Wednesday but remain moderate before possibly accelerating to advisory levels again with another frontal passage on Thursday. A significant WNW swell still looks on track to steamroll the North Coast late this week, with models consistently showing the peak Thursday night of around 16 ft at 18 seconds, before slowly decaying through the weekend. /TDJ && .EKA WATCHES/WARNINGS/ADVISORIES... CA...None. NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 9 AM to 9 PM PST Tuesday for PZZ470-475. && $$ 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

461 FXUS66 KMTR 091720 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 920 AM PST Mon Dec 9 2019 .SYNOPSIS...Dry conditions with mild temperatures are forecast through Tuesday afternoon. Patchy dense fog is likely during the night and morning hours. A weak weather system may produce light rain from late Tuesday into early Wednesday. Dry conditions are then forecast for most of the second half of the work week before rain chances increase by Friday night or Saturday. && .DISCUSSION...as of 9:20 AM PST Monday...Fog continues to impact much of the San Francisco Bay Area this morning. Visibilities at major airports such as San Francisco and Oakland dropped down to as low as a 0.25 mile and 0.125 mile, respectively, earlier this morning. The San Jose Airport managed to avoid the worst of the fog impacts with visibilities only dropping down to 4 miles there. Right now the Dense Fog Advisory for the North Bay Valleys, City of San Francisco, San Francisco Bay Shoreline, San Mateo Coast, and East Bay Interior Valleys is set to expire at 10 AM PST. While dense fog is not expected to be widespread after this time, would not be surprised if a good number of locations still have low clouds and even reduced visibilities beyond mid-day. No major changes have been made to the short-term grids. For additional forecast details, please refer to the previous discussion section. && .PREV DISCUSSION...As of 3:30 AM PST Monday...Primary short-term weather concern from this morning through Tuesday is fog. Plenty of low level moisture from recent rains, in combination with long December nights and a stable airmass, are producing conditions favorable for fog formation. Dense night and morning fog is a potential hazard through at least Tuesday. Dense fog has been reported in the North and East Bay valleys overnight, as well as along the east shore of San Francisco Bay. Dense fog has thus far been patchy and not particularly persistent, so will hold off on issuance of a Dense Fog Advisory for the time being. However, if dense fog becomes more widespread by daybreak, an advisory will be issued. Fog will be a factor during this morning`s commute. In addition to patchy dense fog, areas of low clouds linger this morning. A low December sun angle and lack of mixing will result in slow clearing of low clouds and fog today, and it`s possible some areas will not clear until sometime in the afternoon. Another round of fog is likely tonight and into Tuesday morning as a shortwave ridge over California maintains a stable airmass, and as low level moisture persists. Temperatures over the next few days will remain mild, with highs ranging mostly from the upper 50s to lower 60s, except locally cooler where fog persists. Low temperatures will be mostly in the 40s and lower 50s, except upper 30s in the cooler valleys. Early morning satellite imagery shows a frontal system well offshore along 140W. The models agree that this system will split long before it reaches the coast, with the northern branch of the split moving northeast towards British Columbia and the southern branch tracking eastward and reaching the California coast by Tuesday night. The system is forecast to weaken rapidly as it pushes onshore on Tuesday evening, but the models generally agree that it will maintain enough moisture and lift to generate scattered light rain in our area, particularly in northern coastal areas. Rain could develop by late Tuesday afternoon along the North Bay coast, but the best chance of rain will be on Tuesday evening. A few showers may linger through late Tuesday night or even into early Wednesday. Rainfall totals from late Tuesday through early Wednesday are forecast to be under a quarter inch. The ECMWF is a bit more bullish with rain amounts, forecasting close to a half inch in northwest Sonoma County. A broad low amplitude upper ridge is forecast to develop off the southern California coast by midweek and remain there through Friday. This ridge should maintain dry and mild conditions for most of our area during the second half of the work week. However, to the north of the ridge will exist a moist zonal flow with embedded weak upper level disturbances which may result in light rainfall at times in the North Bay. Rain chances will increase by Friday night or Saturday when the ridge to our southwest weakens and a shortwave trough tracks across northern and central California. It looks as though this system will move through quickly and generate only light rainfall amounts early in the upcoming weekend. In the longer range, both the GFS and ECMWF ensemble mean indicate that a progressive pattern will continue into next week, bringing additional rain chances by Tuesday or Wednesday of next week. && .AVIATION...as of 3:38 AM PST Monday...For 12z tafs. Fog and low cigs have spread overnight with most sites now seeing IFR-VLIFR conditions due to either low clouds or fog. IFR-VLIFR conditions are expected to persist through the morning with low clouds possibly lingering into the early afternoon. VFR conditions forecast for this afternoon before low clouds and patchy fog return this evening. Generally light winds through the period less than 10 kt. Vicinity of KSFO...IFR-LIFR conditions due to combination of low clouds and fog through at least this morning. It is possible either or both of these could last into the afternoon. VFR conditions expected by around 20z-22z before low clouds return overnight. Generally light winds expected through the period at or under 10 kt. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...Patchy IFR/LIFR conditions this morning due to fog and low clouds. Thus far KMRY has generally escaped the low clouds, but satellite imagery shows clouds moving towards the terminal. VFR conditions forecast around 18z-20z before low clouds return this evening. Light E/SE winds this morning before turning onshore by this afternoon. && .MARINE...as of 8:51 AM PST Monday...High pressure will build in from the west into today, keeping winds generally light across the waters. A weak system will then move through the region early this week bringing a chance of showers Tuesday night into Wednesday while winds turn southerly. Moderate northwest swell will persist through much of the week before a larger and longer period northwest swell arrives late this week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...Dense Fog Advisory...CAZ006-506-508>510 Marine Fog Advisory...SF Bay until 10 AM && $$ PUBLIC FORECAST: Rowe/Dykema AVIATION: AS MARINE: CW 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

772 FXUS66 KOTX 091600 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 800 AM PST Mon Dec 9 2019 .SYNOPSIS... Fog and low clouds with dry weather are expected for today and Tuesday under a ridge of high pressure. A weak weather disturbance arrives Tuesday night into Wednesday, followed by wetter and unsettled conditions for Thursday into Friday. && .DISCUSSION... Made a few updates for fog and low clouds this morning. Satellite and web cams shows areas of dense freezing fog along I-90 from Spokane to Ritzville, Moses Lake and Vantage. Temperatures are below freezing regionwide, giving way to the potential for slick conditions this morning. Issued a Dense Fog advisory for this stretch until 10am. 12Z OTX sounding shows this boundary layer moisture as very shallow and should see some improvements through the morning hours. /rfox. && .AVIATION... 12Z TAFS: A moist boundary layer with clearing skies and light winds will allow low stratus and fog to expand into all TAF sites this morning. The 12Z Spokane RAOB indicates this moist layer is very thin and eventual improvement to VFR conditions is expected between 18Z and 20Z at the KGEG/KSFF and KCOE TAF sites before IFR conditions return tonight after 06Z. The KPUW and KLWS TAF sites will experience IFR conditions under stratus until east low level winds begin this afternoon to clear these sites out for the remainder of the TAF period. The KMWH and KEAT TAF sites stand the best chance to remain IFR under stratus with some improvement possible this afternoon before deteriorating again late today as the gradient pools stagnant boundary layer air in these low elevation TAF sites. /MJF && .PRELIMINARY POINT TEMPS/POPS... Spokane 34 28 36 31 38 33 / 0 0 0 30 0 80 Coeur d`Alene 36 30 40 32 39 34 / 0 0 0 30 10 80 Pullman 38 29 41 32 42 35 / 0 0 0 30 10 80 Lewiston 44 31 44 36 46 38 / 0 0 0 30 10 70 Colville 37 23 37 27 38 31 / 0 0 0 20 10 80 Sandpoint 35 29 36 32 37 33 / 0 0 0 40 10 90 Kellogg 36 31 39 33 39 35 / 10 0 0 50 30 80 Moses Lake 36 27 36 28 39 31 / 0 0 10 20 10 60 Wenatchee 36 28 36 29 38 31 / 0 0 20 20 20 70 Omak 37 26 34 29 36 32 / 0 0 0 20 10 60 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Dense Fog Advisory until 10 AM PST this morning for Moses Lake Area-Spokane Area-Upper Columbia Basin. && $$

195 FXUS66 KPDT 091653 AAA AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 853 AM PST Mon Dec 9 2019 Updated Aviation Discussion .UPDATE...Rest of today through Tuesday...A dense fog advisory remains in effect for the Columbia Basin and northern Blue Mountains through noon today with visibilities expected to be a quarter mile or less in some locations. Freezing fog across the Yakima and Kittas Valleys may create areas of slickness on roadways, especially bridges and overpasses. Fog is expected to gradually thin and become more patchy in nature by this afternoon. With an upper level ridge parked over the area tonight, areas of fog will once again develop and may become dense. A weak frontal boundary will approach the area late Tuesday evening with a chance for scattered rain showers and mountain snow showers. Richards && .AVIATION...18z TAFS..VFR conditions are expected at KBDN and KRDM with just some mid and high cloudiness. Otherwise IFR and LIFR conditions are expected at the remaining taf sites in stratus and FG. Some temporary improvement is possible this afternoon and early evening for a few hours before conditions deteriorate again tonight. Winds will be light and vrbl areawide. 78 && .PRELIMINARY POINT TEMPS/POPS... PDT 41 31 38 34 / 0 0 0 30 ALW 41 32 38 34 / 0 0 0 40 PSC 40 32 36 33 / 10 10 10 30 YKM 38 30 35 30 / 0 0 20 30 HRI 44 32 39 33 / 0 0 0 30 ELN 40 29 35 30 / 0 0 20 30 RDM 44 26 45 28 / 0 0 20 50 LGD 43 30 40 33 / 0 0 0 30 GCD 42 30 44 33 / 0 0 0 30 DLS 46 35 41 37 / 0 0 20 40 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Dense Fog Advisory until noon PST today for ORZ044-502-507. WA...Dense Fog Advisory until noon PST today for WAZ026>029. && $$ 75/81/81

408 FXUS65 KREV 091110 AFDREV Area Forecast Discussion National Weather Service Reno NV 310 AM PST Mon Dec 9 2019 .SYNOPSIS... A quiet weather pattern will be in place over the next couple of days as high pressure builds across the region. A weak weather system could bring very light snow showers to the mountains from late Tuesday into Wednesday but little accumulation expected. A stronger weather system could affect the region the end of the week into the weekend. && .SHORT TERM... Quiet weather will settle in the next couple of days as a transient ridge passes through the region today. After burning off stratus decks and patchy fog, clouds will clear through the afternoon as a drier air mass descends upon the Sierra and western Nevada. Valley inversions will develop through Tuesday with bases positioned around 6000-6500 feet. This may limit valley mixing and ventilation which could have some implications on air quality. We will see light winds both in valleys and at ridgetops today, but westerly winds will increase across Sierra ridges staring Tuesday morning ahead of the next (weak) low- pressure system. This low pressure system may provide some light snow showers across the Sierra Tuesday night into early Wednesday before quickly dissipating by mid-morning. Overall, a very weak system with accumulations looking generally to be in the dusting to an inch range. Fuentes .LONG TERM...Thursday onward... Thursday will be quite mild for mid-December ahead of the next incoming system. This system is backed by a weak atmospheric river moisture tap, arriving in two parts the end of the week into the weekend. The first part is mild as the region remains on the warm side of the jet, with snow levels in the 8000-9000 foot range for the end of the work week. The second part will arrive with a cold frontal passage this weekend, with snow levels possibly falling to valley floors behind the front. The cold air will be chasing the exiting moisture, so accumulation below 5000 feet will likely be hard to come by. At this point, overall liquid totals from the two parts only look to be 0.5-1.5" along the Sierra crest, highest from the Tahoe Basin north. The Tahoe Basin could pick up 0.5-0.75" of liquid, with a few hundredths up to around 0.35" for western Nevada and the eastern Sierra. Being that snow levels start so high, the bulk of the snow accumulation will be for the upper portions of the Sierra, but light accumulations are possible for passes and even down to around 5000 feet by the end of the storm. Any snow accumulation can cause major travel headaches, especially given it is a weekend in the holiday ski season. If you do have travel plans, be sure to check back for the latest. Following this system, the forecast gets quiet for a few days, but the flow remains progressive (i.e. stagnant conditions not expected). Ensemble guidance is hinting at chances for another storm around Dec 19-20, with general troughiness and storm chances continuing into the days leading up to Christmas. This agrees with the CPC 8-14 day outlook which favors below normal temperatures and above average chances for precipitation during the timeframe. Christmas travel may be impacted. -Dawn && .AVIATION... Dense fog is in place in the Martis Valley, including KTRK, with a few pockets in valleys of the Sierra and northeast CA. Satellite imagery suggests a few pockets of fog into portions of western Nevada as well, but it doesn`t appear to be affecting any terminal sites. Taking a look at temperature and dew point spreads, it is looking less likely that fog will form in these areas this morning -- about a 30% chance. The remnant low and midlevel clouds, which are obscuring terrain this morning, will continue to clear out today with a few flat cumulus by this afternoon. Otherwise, expect light winds and passing high clouds today. The next system is slated to move into the region Tuesday night into Wednesday bringing light rain and snow along with the return of lower ceilings obscuring terrain. -Dawn && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$ For more information from the National Weather Service visit... http://weather.gov/reno

000 FXUS66 KSTO 091120 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 320 AM PST Mon Dec 9 2019 .SYNOPSIS... High pressure builds over the region on today, which will lead to a period of dry conditions and near average temperatures early this week. Precipitation chances return to areas north of Sacramento on Wednesday with more widespread precipitation expected late in the week. && .DISCUSSION... Skies have cleared as the trough continues to south of the area. IR difference imagery shows an extensive area of dense fog along the eastern edge of the Central Valley extending from about Oroville southward through the San Joaquin Valley. Light northerly flow over the western half of the Sacramento Valley has so far prevented the fog from shifting further to the west. Current temperatures are considerably cooler across most of the area compared to 24 hours ago and range from the mid 20s in the colder mountain valleys to the 40s to around 50 in the Central Valley. Heights will continue to build today as an offshore ridge moves through. This ensures a period of dry weather to start the week with near average temperatures. Valley fog is expected to mix out by mid to late morning. The ridge axis crosses the state early Tuesday before a weak shortwave moves through Tuesday evening into early Wednesday. Moisture seems to be meager so precipitation will be light, mainly focused over the northern Sacramento Valley and into the higher terrain. Any snowfall will lead to little to no accumulations. Ridge briefly rebounds Wednesday, then a wide swath of deep moisture will approach NorCal beginning late Wednesday. Overall lift appears to be rather weak, but increasing warm-advection will likely result in some light precipitation across the northern half of the forecast area and northern Sierra Nevada. Snow levels expected to be over 8K ft, so little to no winter travel impacts expected. && .EXTENDED DISCUSSION (Friday THROUGH Monday)... The extended forecast calls for zonal flow over the area. A weak shortwave disturbance will slide over us on Thursday, dragging a cold front into the region. The chance for showers remains in the forecast at this time, keeping the bulk of any precip over the mountainous regions. A more vigorous trough will dig into the area on Friday. Ensembles remain in good agreement with pushing a cold front south through the area Friday night into Saturday morning. This will be the best chances for widespread precip activity for interior NorCal, with the chance for showers lingering throughout the day on Saturday. Snow levels start off fairly high, but once the front passes through we could see accumulating snow at pass level on Saturday. By Sunday, a shortwave ridge builds over the area which will bring drier weather through Monday. && .AVIATION... A tongue of fog has developed along the eastern side of the Valley, bringing IFR and LIFR conditions to several TAF sites. Farther north and west of this, light north winds are prevalent which has kept fog development at bay. The fog is expected to linger throughout most of the morning, with VFR conditions forecast by early afternoon. && .STO WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 10 AM PST this morning for Central Sacramento Valley-Motherlode-Northern San Joaquin Valley- Southern Sacramento Valley. && $$

000 FXUS65 KMSO 091028 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 328 AM MST Mon Dec 9 2019 .DISCUSSION...A cool, northwesterly flow pattern will remain over the Northern Rockies through the day today, and most of Tuesday. This type of flow pattern is conducive to light snow showers, mainly for the mountains. Some light showers are possible for the valleys, but little to no accumulations are expected. Area mountain passes may see periods of light snow on area roads, though the snow intensity isnt likely to create any impacts to travel. Otherwise, a low stratus deck will keep most locations under cloudy skies, with the sun peeking through occasionally. Patchy freezing fog is also possible during the next two mornings, with isolated areas near bodies of water seeing patchy dense fog. Temperatures will be around normal for this time of the year today, with many locations a few degrees above normal Tuesday and Wednesday. A weak shortwave of energy will slide south out of British Columbia through northwesterly flow Tuesday night and Wednesday. This will introduce more moisture, as well as better atmospheric lift, translating to more widespread snow showers. At this time, the Clearwater Mountains in north-central Idaho and the mountains along the Continental Divide, will see most of the snowfall, but most locations will have a decent chance for seeing light snow. Again, the valleys will see very little accumulations, while the mountains will see a few inches. A very moist system continues to be on tap for Thursday and Friday. The mountains will get hit the hardest with snowfall with amounts exceeding a foot in places. Precipitation will start as snow or freezing rain in the lower valleys, then transition to rain Thursday. Snow levels fall Thursday night and snow showers are expected across much of the region on Friday through the weekend. && .AVIATION...Expect mostly cloudy skies today, with scattered light snow showers for the mountains and valleys throughout the day. Little to no accumulations are expected in the valleys and air terminals. Passing showers may temporarily reduce visibility as they move overhead. Otherwise, a low stratus deck will keep most locations under cloudy skies, with the sun peeking through occasionally. Patchy freezing fog is also possible the next two mornings, with isolated areas near bodies of water seeing patchy dense fog. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$

000 FXUS65 KBOI 091638 AFDBOI Area Forecast Discussion National Weather Service Boise ID 938 AM MST Mon Dec 9 2019 .DISCUSSION...Area of high clouds is on its way out, revealing patchy fog and stratus. Dry and cooler today with northerly flow aloft. Current forecast is on track for today so no update at this time. && .AVIATION...Overall VFR, with pockets of MVFR/IFR in fog and stratus this morning. Areas of fog redeveloping overnight bringing MVFR/IFR conditions to the region. Surface winds: Variable less than 10 kts, except west 10 to 15 kts vcnty KJER/KTWF. Winds aloft at 10Kft MSL: NW 10 to 20 kts. && .PREV DISCUSSION... SHORT TERM...Today through Wednesday...Northwest flow aloft will continue into Tue as an upper level ridge moves toward the area. The ridge axis will pass through the region Tue afternoon and evening. This passage will open the door to an upper level trough moving in Wed, bringing a chance for light snow to much of the area Tue night after midnight through Wed early afternoon. The latest NAM trended notably toward higher PoPs, and the forecast was trended above NBM PoP numbers accordingly. An inversion will develop and strengthen today into tomorrow, bringing an increasing chance of fog/low clouds and small diurnal ranges in temperatures. We do not see the inversion lasting quite long enough to warrant and air stagnation advisory, but it is close. Temps will be slightly above normal through the short term period. Any snow in lower elevations Tue night into Wed will be very light. Overall, changes made this morning were minor. LONG TERM...Wednesday night through Sunday...Models remain in good agreement over the extended forecast, in which an upper level low along the Alaska Coast channels moisture over the Pacific Northwest. Westerly flow aloft will channel in widespread precipitation across the Intermountain West on Thursday and Friday, with showers lingering through Saturday. A trough moves across the region on Sunday, keeping moisture mostly to the south. A brief ridge builds behind the trough, drying out conditions on Monday. Snow levels will stay above 4500 ft MSL through Friday, allowing for rain at most elevations. By Saturday night, snow levels fall to the valley floor and all remaining showers will fall as snow. Temperatures on Thursday and Friday will remain several degrees above normal, while the incoming trough on Saturday will lower temperatures to right around average for early December. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...DG AVIATION.....CR PREV SHORT TERM...SP PREV LONG TERM....AL

000 FXUS65 KLKN 091217 CCA AFDLKN Area Forecast Discussion...CORRECTED National Weather Service Elko NV 417 AM PST Mon Dec 9 2019 .SYNOPSIS...Dry conditions under a ridge of high pressure are expected across the area today and Tuesday. A weak weather disturbance could bring light shower activity to northern Nevada Wednesday before a stronger, more moisture-laden storm system impacts the region late this week. && .SHORT TERM...Today through Wednesday. Mid-level ridge axis moving into the region today will keep NV dry for the next couple of days. Light winds are expected as well under the ridge. A quick moving short wave will move through the Great Basin region Wednesday ushering in more cloud cover and opportunities for rain and snow. However, this fast moving system will result in light precip amounts with minimal impacts. High temperatures will remain in the 40s for the next several days. Lows tonight will be coolest falling into the teens in many valleys with 20s beginning Tuesday night as cloud cover begins to increase ahead of the mid-level trough. .LONG TERM...Wednesday night through next Monday. Confidence increased slightly in the medium range forecast (Wednesday night through Saturday), still a bit iffy in the longer range (Saturday night through Monday). Models bring a series of short waves across the Great Basin Wednesday night through Saturday night, with ample maritime tropical moisture. An atmospheric river appears more likely to set up Wednesday night through Saturday morning with its origin well south of Hawaii near the ITCZ. The current forecast takes this into account with a multiple day snow/rain event in northern Nevada with lower pops over central and eastern Nevada. Total QPF from 12z Thursday through 18z Monday could range from around a tenth inch in central Nevada to a third inch in northwest Nevada, with maxes of 1.0 to nearly 3 inches in places like Jarbidge Wilderness, the Ruby/East Humboldts, and the Independence Range. Actual snow amounts will vary depending on the nature of the surface precip and this will in turn vary depending on the degree of cold advection in the waves coming over the Sierra. At this time, the waves appear to be coming in a quasi-zonal flow, which will limit cold advection. If the worst cast scenario occurs in the total snow amounts, we could be looking at a mix of rain and snow in the valleys with accumulations in the above mentioned time frame of a few to several inches of wet, partially melting snow, to two to three feet in the above mentioned mountains. Again, confidence drops toward the end of the long range. Stay tuned. && .AVIATION...Upper trough axis will continue to move well east and south of Nevada this Monday morning with northerly flow just above the surface. Recent light precipitation and clearing could lead to patchy freezing fog (VCFG) and/or a low stratus deck forming at any of the TAF sites before daybreak. Otherwise, quiet weather will prevail with relatively light winds and mild temperatures for December as a progressive mid-level ridge of high pressure moves through the state on Tuesday. && .LKN WATCHES/WARNINGS/ADVISORIES... None. && $$ 93/98/98