439 FXUS66 KSEW 031105 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 305 AM PST Tue Dec 3 2024 .SYNOPSIS...High pressure aloft will allow for continued dry conditions with morning fog and low stratus. The upper ridge will break down towards the end of the week as the next storm system approaches, bringing in the next chance for widespread precipitation across the region late this week and through the weekend. && .SHORT TERM /TODAY THROUGH THURSDAY/...High pressure aloft will remain firmly in place through Wednesday, maintaining dry and stable conditions with rounds of morning fog and low stratus. Upper level clouds along the periphery of the ridge are limiting the extent of dense fog early this morning, though surface observations show pockets of greatly reduced visibility. Cold overnight lows will also give way to the development of freezing fog in areas that fall below freezing this morning, primarily south of the Puget Sound. The forecast will continue to see little change day to day, with highs in the upper 40s to lower 50s and lows near freezing across the lowlands. A pattern change is on track for Thursday and beyond, with more active weather settling back into the region. An upper level trough will override the high pressure ridge on Thursday, bringing in a quick shot of rainfall to western Washington. This system will increase mixing that will help to erode the ridge and scour out the lower level air mass that has brought fog each morning. .LONG TERM /FRIDAY THROUGH MONDAY/...A warm front will lift across the region on Friday, bringing in widespread rainfall with snow levels near 7000-9000 ft. Temperatures Friday will peak well into the 50s across the lowlands. A cold front will follow closely behind on Saturday as an upper level trough settles over the region, bringing in more precipitation and lowering snow levels to 3000-3500 ft by Saturday night. Forecast models shift a cutoff low inland on Sunday, with a majority of continued shower activity occurring over the northern Cascades. A ridge is on track to develop inland towards the beginning of next week, drying things out as northerly flow aloft keeps cooler temperatures in place. 15 && .AVIATION...Upper level ridging over the region will keep flow aloft in the midlevels light and zonal. Surface winds are primarily light and variable for the interior terminals and lightly offshore for terminals along the south interior, coast, and Strait of Juan de Fuca. Conditions are largely IFR to LIFR early this morning with another round of widespread fog redeveloping across western Washington. Conditions will likely remain IFR to LIFR through the morning hours, though guidance does continue to indicate a return to more widespread MVFR to VFR conditions by mid afternoon/early evening. Confidence in this improvement trend remains low given the trends over the past few days and the stagnant weather pattern. Some spots may see fog linger in places throughout the day. Light offshore flow may help to dry out the lower levels somewhat, but guidance shows another round of fog redeveloping across the interior Tuesday night into Wednesday. KSEA...Conditions LIFR in fog. Fog looks to linger through the morning hours, with guidance hinting at improvement towards MVFR/VFR by the mid to late afternoon hours. Given trends over the past few days, however, confidence in improvement remains low. Winds will remain light at 6 kts or less and primarily out of the N/NE through the TAF period. 14 && .MARINE...High pressure will remain situated across the area waters through midweek, keeping winds generally light and offshore through Wednesday. Widespread fog redeveloping nightly could limit visibilities to less than 1NM over portions of the waters today and again on Wednesday. Seas will primarily hover between 5-8 ft through midweek. The next frontal system will approach the coastal waters on Thursday with another, stronger system slated to move into the waters Friday into the weekend. The system on Friday will bring stronger southerly winds to the coastal and north interior waters and will allow for seas across the coastal waters to build to 10-15 ft. 14 && .HYDROLOGY...An upper ridge will remain in place across Western Washington through Wednesday. A frontal system will move through on Thursday for lighter QPF amounts. Another weather system Friday into Saturday is forecast to bring heavier QPF amounts. In addition, snow levels are expected to rise later Friday into early Saturday to 7000 to 9000 feet. This, combined with rainfall, will result in rises on rivers across Western Washington. At this time, the Skokomish River is the main river of concern for potential river flooding during this period. However, other area rivers will need to be monitored due to the higher snow levels Friday into Saturday. JD && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$

087 FXUS66 KPQR 031715 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 915 AM PST Tue Dec 3 2024 Updated Aviation Discussion .SYNOPSIS...High pressure over the region will produce dry weather through at least Wednesday, with areas of clouds and fog in the interior valleys and sunshine elsewhere. Rain chances start to increase Thursday/Friday into the weekend with snow levels remaining above the Cascade passes through Saturday. && .DISCUSSION...Little change in the overall pattern as high pressure persists over the region this morning. Satellite imagery and surface observations from around the area paint a nearly identical picture to the past several nights, with widespread stratus and fog across the central and south Willamette Valley and also the Cowlitz and Lower Columbia River Valleys of southwest Washington. Easterly flow through the Columbia River Gorge continues to keep the Portland/Vancouver metro mostly clear, although a small sliver of stratus is noted moving up the Columbia towards the area as of 3 AM Tuesday. Temperatures are dropping into the 20s with patchy frost formation being observed in a few locations that are more sheltered from the wind. Expect more of the same today and Wednesday as stratus and fog remain trapped in the same areas beneath a strong subsidence inversion at around 1000 feet. Air stagnation issues will persist in these area through Wednesday as a result, with daytime temperatures continuing to struggle to get out of the 30s in the central and south Willamette Valley. Meanwhile, a TTD-DLS pressure gradient of -6 to -7 mb will maintain breezy conditions through the western Gorge through Wednesday, producing wind gusts to around 30 mph at times in eastern parts of the Portland metro and gusts as high as 60 mph at favored locations within the Gorge such as Corbett and Crown Point. This will also continue to keep the Portland area under mostly sunny skies, allowing afternoon temps to climb into the upper 40s each afternoon. Medium range guidance continues to hint at some changes in the pattern by Thursday as models are starting to come into better agreement on the ridge weakening enough to allow a weak upper level disturbance to cross the area on Thursday. It remains to be seen if this will result in any precipitation returning to the area as global ensembles have actually trended a bit drier for Thursday and Friday in recent runs, but there are still enough members depicting precipitation to keep a 20-30 percent chance of rain inland and a 50-60 percent chance along the coast for the latter half of the week. Regardless of how the forecast unfolds, any impacts look to be minimal as QPF amounts remain light and snow levels stay well above the Cascade passes. At the very least, the passing disturbance will be enough to weaken the subsidence inversion and finally put an end to air stagnation issues while scouring the stratus and fog out of the interior valleys. This will result in milder temperatures for Thursday and Friday, with overnight low more commonly in the upper 30s to low 40s as we head into the weekend. The weekend will also bring increasing chances for precipitation as the ridge axis finally shifts east of the Cascades and allows an upper level trough to potentially approach the region late Saturday into Sunday. /CB && .AVIATION...High pressure and low level inversions continue to bring air stagnation and minimal changes to the forecast. Persistent IFR/LIFR conditions within the Central and Southern Willamette Valley and given the minimal changes in the pattern expect those conditions to persist through at least 18Z Wednesday, with a 10% probability of a brief period of improvement starting around 20Z Tuesday. Elsewhere, conditions should improve to VFR around 18Z-20Z Tuesday or maintain said VFR conditions. Easterly winds through the Columbia River Gorge and elevations within east/west aligned terrain will continue to gust up to 35 kt, with some elevated areas seeing gusts up to 50 kt. Fog expected to return later tonight and will result in a 10-25% probability of IFR/LIFR conditions returning to the Northern Willamette Valley. In addition to the fog, at or below freezing temperature mean that fog will freeze on surfaces. Cannot rule out a little rime icing in locations where temperatures are the coolest. PDX AND APPROACHES...VFR with a 10%-20% probability of IFR/LIFR fog returning around 12Z-15Z Wednesday. Easterly approaches will see gusty easterly winds. Surface winds will stay easterly and under 10 kt. /42-Hall && .MARINE...High pressure continues, keeping mild conditions over all seas through at least Wednesday night. Winds will remain under 10 kts and seas around 5 feet at 13 seconds until then. Expect strong ebbs to return to the Columbia River Bar around 5PM Tuesday, but with seas under 7 feet expected, will refrain from issuing a Small Craft Advisory. Early Thursday morning, a weak front passing through the area will briefly elevate southerly winds, giving a 40% chance of Small Craft Advisory criteria being met. Another round Friday through Saturday will bring much higher chances of Small Craft Advisory criteria being met as this system will elevate seas to around 10 feet. ~Hall && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until 4 AM PST Thursday for ORZ104-105- 108-109-113>118-123>125. Freezing Fog Advisory until 11 AM PST this morning for ORZ114>118. WA...Air Stagnation Advisory until 4 AM PST Thursday for WAZ202- 204>206-208. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland

946 FXUS66 KMFR 031122 AFDMFR Area Forecast Discussion National Weather Service Medford OR 322 AM PST Tue Dec 3 2024 .DISCUSSION...Low clouds and fog have made a return tonight with visibility at a half mile or less in the Rogue Valley and Umpqua Basin as of 3 AM. Agree with the evening meteorologist that there will still be fog/freezing fog in west side valleys and near Klamath Falls until the late morning. Considering the conditions this afternoon, the Grants Pass area and the Illinois Valley could have harder clearing out as well as other valleys. The chance for better visibility will continue through the afternoon before lowering again later in the afternoon in similar areas as the past few days. Considering this, keeping the expected warmup with 40s for valleys and 50s elsewhere. Temperatures in the mid-30s in Coos County as of 3 AM show that frost conditions will come tonight with a Frost Advisory in effect until 9 AM. After, high temperatures will be in the 40s and 50s with more 40s east of the Cascades. More sunshine will be found outside of the valleys with mild afternoon temperatures through the week. The stronger ridge present will stay on the west coast through Wednesday, so the Air Stagnation Advisory will continue until then. After, a disturbance will move through the PNW Thursday, but recent updates show this will be impacting farther western areas while it enters the region. Rain chances for this will be at the coast with lighter amounts. There is agreement that there will be precipitation at the start of the weekend as a trough moves inland from the north, but it will weaken as it does. There is more agreement that there will be precipitation Saturday with more uncertainty on how much lingers for Sunday. For now, the impacts will be lighter precip near and west of the Cascades. Temperatures will stay mild through the long term. -Hermansen && .AVIATION...03/12Z TAFS...LIFR stratus and fog have returned to the Coquille, Umpqua, Rogue, Illinois, Applegate, Scott, and Shasta valleys, including both Roseburg and Medford. It will continue to expand in coverage into sunrise though the LIFR in the Coquille Valley is not expected to quite reach North Bend. Patches are also expected to intrude into Klamath Falls early this morning, with VFR returning before the end of the morning. Elsewhere, it will likely take a little longer. But, similar to what transpired Sunday, we have VFR expected by the afternoon. Valley LIFR is likely to return again around 05-08Z this evening, into Wednesday morning. -DW && .MARINE...Updated 200 AM PST Tuesday, December 03, 2024...Light to moderate north winds and relatively calm swell dominated seas will persist into Wednesday. A weak front is expected to pass by to the north Thursday, into the northern Oregon waters, with winds shifting to southerly. Seas will build with west swell dominated seas are expected to be just shy of becoming steep during their peak on Thursday night. Another slightly stronger front will likely move through Friday night into Saturday morning with the highest winds and seas north of Cape Blanco...approaching advisory levels on Saturday. A third front is forecast to be the strongest of the bunch with high and steep swell dominated seas possible early Sunday into early Monday. -DW && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Frost Advisory until 9 AM PST this morning for ORZ021. Air Stagnation Advisory until 4 PM PST Wednesday for ORZ023-024- 026-029>031. CA...None. PACIFIC COASTAL WATERS...None. && $$

735 FXUS66 KEKA 031219 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 419 AM PST Tue Dec 3 2024 .SYNOPSIS...Relatively clear, warm and dry conditions expected through midweek. A weak shortwave will move through the region Wednesday and Thursday, producing light drizzle along the north coast. Chances for rainfall or drizzle increase through the weekend. && .DISCUSSION...Cloud cover cleared out Monday with the departure of a weak upper low. With a strong ridge of high pressure firmly in place, overnight lows dropped to chilly but seasonably normal levels in the lower elevations. The ridgetop temperatures have been much milder above the inversion. Expect very similar conditions through Wednesday. Coastal stratus and fog will begin increasing in coverage tonight. A weak shortwave will clip the region Wednesday night, mainly increasing cloud cover. Some light showers and coastal drizzle will also be likely, but precipitation accumulations will be highly limited with chances for over 0.1 inch of rainfall less than 20%. The ridge will further amplify late this week, and daytime highs will be warm, pleasant and much above climatological averages. There are indications the coastal stratus and possible fog will regain more of a presence, and this would suppress highs for portions of the coast. A stronger system will impact the Pacific Northwest through the weekend, with some of it likely clipping N CA. Probabilities for a wetting rainfall over a tenth for an inch go up to 40 to 65%, but significantly drop for over 0.3 inches. Orientation of steering high pressure will determine how much moisture makes it to the coast; elevated PWAT values are available just offshore within a weak AR-type feature. Cluster and ensemble members show strong evidence the trough will then drop into the Great Basin as an inside slider going into next week, and this pattern is favorable for amplified offshore winds. /JJW && .AVIATION...At coastal terminals, little to no wind is expected into early this morning. This lack of wind will increase the possibility for the development of lower clouds and dropping visibilities. There has still been some periods of light offshore flow early this morning at both KACV and KCEC, which is helping to stave off low cloud development. By mid morning, any potential for decreased ceilings and visibility at the coast will diminish with VFR conditions expected through the daylight hours. With high pressure building back in throughout the day, stratus development is more likely at the coast overnight tonight. Interior valleys are expected to have foggy/misty conditions into mid morning, particularly the Trinity River valley. There is a potential for MVFR conditions around KUKI, but models indicate that VFR conditions are expected for most of the forecast period. /JLW && .MARINE...A long period W swell continues to diminish into the middle of the week. Winds continue at 5 - 10 kts out of the north, at least through Tuesday. Short range models are indicating a weak expansion fan developing downwind of Port Orford and Cape Mendocino today and into Wednesday, briefly generating 15 to 20 knot gusts in the outer waters. However, significant wave heights will likely remain below advisory levels through late this week despite additional long period NW swells filling into the waters Thursday and Friday. Models are still inconsistent regarding elevated northerly winds during this period late week. && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... None. && $$ 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

887 FXUS66 KMTR 031146 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 346 AM PST Tue Dec 3 2024 ...New AVIATION, MARINE... .SYNOPSIS... Issued at 157 AM PST Tue Dec 3 2024 Above normal temperatures and dry conditions will continue to prevail through the week. && .SHORT TERM... (Today and tonight) Issued at 157 AM PST Tue Dec 3 2024 GOES-West Nighttime Microphysics tells us all we need to know, let`s take a look from north to south. A weak low pressure system situated over the North Bay is bringing mid-level clouds to Northern California, stratus can be seen developing along the Big Sur Coast and spreading northward, and a mid-level cloud shield associated with a weak low pressure system off the California/Mexico border is extending into the Desert Southwest. Aside from that, generally clear skies and calm conditions are being observed across the region. Because of this, patchy dense fog will likely develop in favorable coastal and valley locations with some already being observed on the ALERTCalifornia cameras in the Russian River Valley. While Watsonville Airport is not yet a climate site due to it being too young (less than 30 years old), it did break a record for daily maximum temperature on December 2nd by reaching 72 degrees, breaking the previous record of 70 degrees set in 2006. The warming trend continues with Oakland Museum forecast to reach 68 degrees today which would break the previous daily maximum temperature record of 67 degrees set in 2014. && .LONG TERM... (Wednesday through Monday) Issued at 157 AM PST Tue Dec 3 2024 A Rex Block pattern will develop as a ridge of high pressure continues to build across the West Coast and low pressure develops over the Desert Southwest allowing for above normal temperatures and dry conditions to prevail. The first of a pair of shortwaves set to skirt the region will bring increasing cloud cover and a slight chance of precipitation to the northern outer waters on Thursday. The second shortwave on Saturday is expected to be stronger, bringing the warming trend to a halt with slight chances of precipitation extending across the outer waters and moderate northerly breezes developing. To no avail, it is likely that a ridge of high pressure will develop again in the wake. && .AVIATION... (12Z TAFS) Issued at 336 AM PST Tue Dec 3 2024 VFR is expected to prevail through the forecast period with the exception of KSTS which is seeing occasional drops into LIFR with fog in the area, which is expected to lift within a couple hours after sunrise. Vicinity of SFO...VFR conditions persist with weak surface winds. When diurnal winds increase slightly after sunrise, expect weak offshore flow this morning, eventually becoming weak onshore flow this afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR is expected to prevail with weak offshore winds this morning eventually becoming weak onshore flow this afternoon. && .MARINE... (Today through Sunday) Issued at 336 AM PST Tue Dec 3 2024 Long period northwest swell will persist through the week with light to moderate north winds resulting in a light to moderate sea state. No other majore hazards expected. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...Sarment LONG TERM....Sarment AVIATION...JM MARINE...JM 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

346 FXUS66 KOTX 031057 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 257 AM PST Tue Dec 3 2024 .SYNOPSIS... A dry and stable weather pattern will persist through the middle of the week, and temperatures seasonably cool in the upper 20s to mid 30s. Chances are increasing that the ridge of high pressure will weaken by the weekend with a return of light precipitation. && .DISCUSSION... Today through Thursday night: Persistent upper level ridge of high pressure remains in place. Initially the ridge ridge axis remained rather broad coming into the workweek however ensemble models suggest minor disturbances overtopping it and as a result the axis retrogrades back a bit towards the British Columbia coast Tuesday but then it rebounds and is over the Cascade Crest Wednesday. A more pronounced frontal feature with a capable, but not very strong, moisture tap is expected to push thru Thursday/Thursday night and may allow some light mountain snow and a mixed wintry mix of precip for lowlands and valleys. The mixing brought about by the passage of the Thursday/Thursday night feature allows for some potential for less clouds and warmer temperatures. /Pelatti Friday to Monday: The Inland NW will be moving into a more active pattern with several opportunities for mountain snow and valley mix, with Saturday being the wettest day. A warm front lifts in Friday, before a cold front pushes by Saturday. With Friday`s warm front the main precipitation chances will be found near the Cascades to Waterville Plateau and northeastern WA/north ID mountains. Precipitation chances increase throughout the area Friday night into Saturday morning, with precipitation likely by Saturday over most of the region and chances remaining high into Saturday evening. The lowest risk will be found in the deeper basin and L-C Valley. Ahead of any of this precipitation, there will be potential for patchy fog/freezing fog and out of that could be squeezed some drizzle/freezing drizzle or flurries over the Columbia Basin/Palouse/Spokane/CdA area as milder air overruns a moist boundary layer. * Precipitation-type: this will be somewhat tricky. Overall milder temperatures move into the area through Saturday and a lot of that is expected to be found at the surface and aloft. However colder air may linger near the Cascades and northern valleys. Primarily look for a lowland snow or a rain/snow mix Friday and Friday night into Saturday AM, except for all rain toward east- central and southeast WA and the central and southern Panhandle as that risks increases Friday night into Saturday. Mountains will see mostly snow, but milder air in the Cascades and central Panhandle will keep that snow largely in the higher peaks. Heading into Saturday afternoon it looks likely mainly lowland rain and high mountain snow. The tricky part the freezing rain potential. I did increase a chance for freezing rain around the north Cascades, largely around the Methow Valley and nearby areas, and in some of the sheltered valleys toward the Canadian border. Ensembles continue to show a 20-60% chance of at least a 0.01 inches of inch. Overall confidence in amounts of ice, if any, is low but more than trace amounts are possible. There is a broad spread in what models depict in this regard. Some ensembles show no risk at all and others a broader risk, a risk that expands to more of the Columbia Basin into the Spokane area. This is not entirely out of the question, but at this point seems like less than a 10% chance away from the aforementioned areas. Saturday overnight into early Sunday precipitation chances remain modest away from the lee of the Cascades, but overall they begin to wane. Heading into Sunday and Monday the threat of precipitation retreats to the mountains zones and largely ends outside of these by Monday. Cooler air comes back in, featuring the potential for lowland rain/snow mix and mountain snow, save for mainly rain over the southeast WA and lower ID Sunday afternoon. Additional fog is forecast behind the precipitation with the continued moist boundary layer. Saturday and Sunday will be breezy, with winds gusting around 15-20 mph in unsheltered areas. Temperatures are expected to be above normal through Sunday, with highs in the 30s to mid-40s. The warmest day looks like Saturday with some low 50s around the L-C Valley. Overnight lows will be in the 20s and 30s. Temperatures cool closer to normal by Monday. /Solveig && .AVIATION... 12Z TAFS: IFR stratus continues to cover most of the region, with MVFR stratus over KEAT and KOMK. Little to no change expected. The lowest visibilities will occur where the stratus intersects the terrain, which is elevations between 2200 and 3500 feet, which includes KGEG/KPUW. For these two sites visibility down to 1/4SM with FZFG will be common for most of the TAF period. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high of stratus plaguing the region through 12z Wed, with widespread IFR/MVFR conditions. With some fluctuations in the boundary layer wind around KPUW there is lower confidence with if and for how many hours 1/4SM visibility occurs. ----------------------- 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 31 28 32 28 36 27 / 10 10 10 10 10 10 Coeur d`Alene 33 29 34 29 38 27 / 10 10 10 10 10 10 Pullman 33 28 34 28 39 29 / 10 10 10 10 10 10 Lewiston 37 32 38 32 43 32 / 10 10 10 10 0 0 Colville 33 26 34 26 36 23 / 10 10 10 10 10 10 Sandpoint 35 28 36 28 38 26 / 10 10 10 10 10 10 Kellogg 40 31 41 31 43 32 / 0 0 0 0 10 10 Moses Lake 35 31 36 32 33 24 / 10 10 10 10 10 0 Wenatchee 33 30 34 30 38 29 / 10 10 10 10 10 0 Omak 33 29 34 29 38 27 / 10 10 10 10 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$

595 FXUS66 KPDT 031148 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 347 AM PST Tue Dec 3 2024 .Updated Aviation Discussion. .SHORT TERM...Today through Thursday night...Models and ensemble clusters are in excellent agreement on the evolution of the 500 mb pattern during the short term period. An upper level ridge will remain over the region through Wednesday. This provides high confidence (80-90%) that the extensive stratus layer will remain in place the next couple of days...though the southern edge will likely oscillate north and south. This will have the biggest impact on the Bend/Redmond population centers with periods of freezing fog. High and low temperatures will be modulated by the extent/persistence of the fog/stratus. Most of the current fog/freezing fog concerns are where the stratus layer is intersecting the terrain at elevations of 2000-3500 feet MSL. The current freezing fog advisories remain in effect and a special weather statement was also issued for interstate-84 east of Pendleton for dense freezing fog and slick roads. For this forecast ended fog after 18Z Wednesday though this may be a bit optimistic. Wednesday afternoon the ridge begins to shift eastward as a shortwave trough approaches the area which may help break up the fog. This feature will only briefly flatten the 500 mb flow and perhaps bring a chance of mainly rain showers to the Cascade crest Thursday and Thursday night. The NBM currently has 15-30% POPS for this area with the clusters only showing .01-.03 inches of QPF. With such a weak system anticipated and a ridge forecast to rebuild right behind it, there is a decent chance (40-50%) that the low stratus does not get scoured out completely or at least remains in Washington through Thursday and then expands into northern Oregon Thursday night. This scenario will have to be evaluated in future forecasts. 78 .LONG TERM...Friday through Tuesday... Key Messages: 1. Widespread rain chances and mountain snow Saturday into Sunday. 2. Breezy winds Saturday evening through Sunday morning. 3. Near to above normal temperatures through period. Ensemble and deterministic guidance is in good agreement with the overall synoptic pattern of an upper level trough approaching the coast and passing through the Pacific Northwest Saturday into Sunday morning. This system will bring a more active pattern to the region, allowing for widespread rainfall, mountain snowfall, breezy winds, and warm temperatures over the weekend. A warm front will pass over the area ahead of the upper level system on Friday, attributing to snow levels rising to 8000-9000 feet as rain chances (50-70%) stay confined along the Washington Cascades. The upper level trough and attendant cold front will then approach the Washington coast on Saturday, pushing across the area as the trough begins to broaden and dig into northern Nevada by Sunday evening. The cold front will lead to snow levels dropping to 3000-4000 feet by Sunday morning. Thus, mountain rainfall will transition to snow Saturday evening as 1-3 inches of snowfall is anticipated to fall along the Cascade passes through Sunday afternoon. Confidence in these snow amounts are moderate to high (60-80%) as the NBM suggests a 45-55% chance of 1 inch of snow across Santiam and Snoqualmie Passes between 4 PM Saturday and 4 PM Sunday. Higher elevations of the Cascades and northern Blue Mountains are expected to pick up 2-5 inches of snowfall above 4000 feet. Widespread rain chances (25-65%) will materialize through Saturday morning, with lower chances (25-35%) expected across Central Oregon. Saturday does look to be the wettest day in the forecast, with 0.30-0.60" of rainfall anticipated along the Cascade and northern Blue Mountains, 0.03-0.15" along the Blue Mountain foothills and the John Day-Ochoco Highlands, and 0.02" or less over the Lower Columbia Basin. Areas of Central Oregon, especially the Bend/Redmond area, will likely stay dry over the weekend. Confidence in these rain amounts is moderate (60-70%) as the NBM advertises a 45-75% chance of 0.40" of rainfall over the Cascades and northern Blues, a 40-60% chance of 0.10" of rainfall along the northern Blue Mountain foothills, and a 50-70% chance of measurable rainfall (0.01" or more) across the Lower Columbia Basin. The surface cold front will continue to exit to our southeast into Sunday morning as the upper level system encroaches into northern Nevada and California. Surface high pressure will slide onshore an into Central Oregon behind the cold front, which will keep precipitation chances (20-50%) along the Cascades, east slopes, John Day-Ochoco Basin/Highlands, and the Blue Mountains and foothills. Rain accumulations will stay confined at elevation across our mountain zones, with 0.05-0.25" of rainfall likely on Sunday. The passing cold front on Saturday will set up a pressure gradient across the Columbia Basin (KPDX-KGEG) of 5-5.5mb as advertised by the GFS. This will lead to elevated winds across the Basin, with the highest winds expected along the east slopes of the Washington Cascades, Simcoe Highlands, Blue Mountain foothills, and the northern Blue Mountains, peaking late Saturday night into the early morning hours on Sunday. This cross-basin gradient of 5-5.5 mb is much less than the normal advisory threshold of 11 mb, but will still lead to sustained west winds of 15-20 mph with gusts of up to 30 mph. Winds will increase through Saturday afternoon and evening, peaking overnight before slowly subsiding through Sunday afternoon. Upper level flow will stay consistently out of the west-southwest through the weekend, which will lead to warmer air advecting into the area. This will allow for near to above normal high temperatures to return to the area Friday through Sunday. As the upper level trough digs into Nevada and California, flow aloft turns more from the north to allow a cooling trend to commence as cooler, Canadian air brings high temperatures back to near normal by Tuesday. Overnight cloud cover associated with the upper level system will help to keep low temperatures near to slightly above normal, with the warmest morning in the forecast occurring on Sunday. Ensemble clusters are in fairly good agreement, but there are minor differences in relation to the strength of the upper level ridge early in the period on Friday. This ridge is what breaks down over the weekend as the upper level trough passes through the area. 57% of ensemble members hint at a stronger ridge on Saturday, which would cause slightly drier conditions along the east slopes and Basin. Upper level ridging slides into the area Monday, in the wake of the dropping and departing weekend system. This will help to bring drier conditions, calmer winds, and cooler temperatures to the area early next week. 75 && .AVIATION...12z TAFs...The status quo from the last couple of days continues on as ridging sits over our area and the low stratus deck continues to linger. BDN has seen FZFG enter the area briefly bringing conditions to LIFR before finally settling back to VFR, which we will expect to continue so for the rest of the period. However the rest of the terminals will continue to experience lower ceilings and visibilities going into the period. DLS, YKM, and ALW will experience reduced ceilings, but will be remain in MVFR through the period. There is a moderate chance (50-60%) that ALW will degrade to LIFR due to reduced ceilings of OVC004 this afternoon, which is expected to extend through the remainder of the period. PDT will remain well within IFR, while RDM will be more obscure with LIFR. && .PRELIMINARY POINT TEMPS/POPS... PDT 32 28 32 27 / 0 0 0 0 ALW 33 30 33 29 / 0 0 0 0 PSC 36 33 35 32 / 0 0 0 0 YKM 34 28 32 26 / 0 0 0 0 HRI 37 33 37 30 / 0 0 0 0 ELN 33 25 32 25 / 0 0 0 0 RDM 37 16 40 19 / 0 0 0 0 LGD 46 27 40 25 / 0 0 0 0 GCD 48 29 47 26 / 0 0 0 0 DLS 39 33 35 31 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Freezing Fog Advisory until 11 AM PST this morning for ORZ508- 510-511. WA...None. && $$ SHORT TERM...78 LONG TERM....75 AVIATION...95

169 FXUS65 KREV 031038 AFDREV Area Forecast Discussion National Weather Service Reno NV 238 AM PST Tue Dec 3 2024 .SYNOPSIS... * Strong inversions will allow for lighter winds and cold overnight low temperatures across the region this week. * Freezing fog persists this week, becoming more extensive where it has lingered for the last couple of days. * Although no significant storm is projected for the next week or two, a possible inside slider system may bring increased winds this weekend. .DISCUSSION... Based on the 03/00Z KREV sounding along with the ensemble forecast soundings going through this week, temperature inversions look to persist across the region that will strengthen during the overnight hours and going into the morning. Due to this setup, the CWA looks to see light winds persist along with cool overnight temperatures. Areas of freezing fog and stratus are still in the forecast for the next couple of days during the overnight and into the morning hours particularly in the valley areas. Those traveling through the region during these times may want to use caution as not only could visibilities be reduced, but surfaces may also be slick. A Freezing Fog Advisory continues this morning for valley portions of the CWA north of I-80 observing these conditions (which shows up pretty well on the Night Fog satellite imagery). For more detailed information, please see the Advisory product. Air stagnation will also continue as ventilation and mixing remains poor to marginal with the inversions in the area. When looking at the latest RAP analysis of the upper air pattern, an upper air low is currently just to the west of the Bay Area while a large ridge resides over the western CONUS this morning. The GEFS and ECMWF ensembles both forecast the low to take a track across CA and make it over AZ by Wednesday allowing for a Rex Block pattern to setup and the stagnant conditions to continue in the region. This still looks to be the case through at least Friday when the AZ low continues a eastern progress allowing for a ridge to move in over the CWA that lasts into Saturday. As a result of this, daytime temperatures for the CWA may warm by a degree or two at the start of the weekend. Deterministic forecast guidance then shows a Pacific Northwestern trough moving into the picture late Saturday that appears to take an "inside slider" track going through Sunday and Monday. While this is not present in the GEFS and ECMWF ensembles at the moment, the system appears be a potential pattern changer for the CWA as it signals winds to possibly pick up a bit on Sunday allowing for some mixing. Temperatures also start to trend cooler too starting Sunday night with this trend continuing into Monday and Tuesday. As for precipitation chances, they still look low going into next week with high pressure in the area. The exception does appear to be on Saturday ahead of the potential trough in areas along the OR border as they may see a slight chance (10-15%) for light precipitation possible during the afternoon. Little to no QPF is expected with this at this time. Will continue to monitor this potential system for the beginning of next week as it could break up the stagnant conditions seen in this week`s forecast. -078 && .AVIATION... High pressure across the region will continue to bring strong inversions today that allow for dense morning freezing fog as well as areas of afternoon haze along with minor reductions to slantwise visibility. While most area TAF sites look to stay mostly VFR with light winds today, lower valley areas of western NV and the Sierra will see periods of IFR/LIFR conditions through this morning due to lower stratus ceilings and areas of dense freezing fog. Areas of particular interest continue to be across the Honey Lake Basin, Pyramid Lake area that stretches north through the Black Rock/Smoke Creek Deserts, and south to Fernley/Dayton where lower terrain is currently or will be obstructed due to the areas of dense freezing fog. Foggy conditions will continue through this morning and do expect to not dissipate until around 03/16-18Z. The cycle of freezing fog for these valley areas does look to repeat again tonight into Wednesday morning though the timing may not be exactly the same. Will continue to monitor this and update the forecast when details become more apparent. -078 && .REV Watches/Warnings/Advisories... NV...Freezing Fog Advisory until 11 AM PST this morning NVZ003>005. CA...Freezing Fog Advisory until 11 AM PST this morning CAZ071. && $$

417 FXUS66 KSTO 031018 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 218 AM PST Tue Dec 3 2024 .SYNOPSIS... Areas of low elevation morning fog persist through much of the week ahead alongside otherwise dry and gradually warming weather. .DISCUSSION... As of early this morning, GOES-West satellite imagery shows some mid to upper level clouds lingering across the central and northern Sacramento Valley with clear skies observed elsewhere. This will allow for another night of radiational cooling, although with slightly higher observed dewpoints compared to last night, low temperatures are expected to settle in the upper 30s to mid 40s across the Delta, Valley, and foothills. Given the more uniform near surface moisture through the Valley from roughly Chico southward, another morning of patchy to scattered fog development will be possible. Current probabilities of dense fog development sit around 20% to 40% for Valley locations from Chico southward and generally along and east of Interstate 5. Currently the only visibility obstructions as of 1 am PDT are across the Sacramento metro and into the northern San Joaquin Valley. Be sure to allow for extra time during your morning commute and check the latest road conditions at quickmap.dot.ca.gov! Any fog that does develop is expected to dissipate moving toward the late morning period, leading to mostly clear skies through the remainder of the day. While the upper level pattern itself remains somewhat active as a closed low moves across SoCal through midweek, interior NorCal is expected to remain primarily influenced by ridging aloft. This will result in the overall stagnant weather pattern that has been observed the last few days continuing through the remainder of the week ahead. High temperatures are expected to remain firmly in the 60s to low 70s across the Delta, Valley, and foothills, as 50s to low 60s persist at higher elevations. Light north to east winds will also continue within this weather pattern, although some breezier east to northeast winds gusting to 25 mph will remain possible along the Sierra during the evening and overnight hours. While fire weather concerns are currently not anticipated given recent precipitation, low afternoon humidity values are also expected throughout the foothills and mountains. .EXTENDED DISCUSSION (Saturday THROUGH Tuesday)... Moving into the weekend, ensemble guidance continues to indicate a lobe of amplified ridging translating eastward, with ensembles then showing some slightly differing solutions as a shortwave ejects out of the Pacific Northwest late weekend into early next week. The primary difference is in regards to the trajectory of the ejecting trough, with some guidance keeping the shortwave rather progressive and some guidance deepening a portion of the trough toward the Four Corners and Great Basin. The former solution would yield little to no impacts for the region, while the latter solution would introduce some potential for gustier northerly winds on Sunday and Monday. Cluster analysis currently depicts a near even split between these solutions. Regardless, both solutions do indicate some lowering heights aloft, which will result in temperatures cooling by around 2 to 4 degrees moving toward next week. && .AVIATION... Areas of MVFR/IFR with localized LIFR due to FG/BR across the Valley from KMYV southward, gradually improving after 18Z. Light north winds less than 12 kts expected through the Valley. Over the Sierra mountains/foothills periodic gusts of 15-25 mph will continue until 18Z today before redeveloping by around 03Z Wednesday. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$

717 FXUS65 KMSO 030950 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 250 AM MST Tue Dec 3 2024 .DISCUSSION... KEY MESSAGES: - Ridge of high pressure through mid week causing stable conditions with valley fog and stratus. - Pattern change at the end of the week into the weekend. The ridge of high pressure continues over the Northern Rockies through Thursday. Latest satellite imagery is showing that fog and low stratus has settled over most valleys of northwest Montana and along the Clearwater River & Dworshak Reservoir in north central Idaho. The fog and stratus is anticipated to erode somewhat each afternoon but increase in coverage and thickness each night through at least mid week. Travelers should beware of reduced visibilities and a few slick spots associated with dense freezing fog. A very subtle feature is expected to slide over northwest Montana today. This feature has the potential to interact with the stratus cloud deck to cause localized flurries and/or freezing drizzle, but impacts should be minimal. The models continue to advertise that a weak plume of moisture moves into north central Idaho and northwest Montana Thursday night into Friday. The atmospheric profile for northwest Montana shows that precipitation should stay mainly snow. While north central Idaho has a better chance of having rain in the valleys and snow in the higher terrain. Overall, precipitation amounts look to remain very light. A more robust push of moisture is expected Saturday. The disturbance associated with this moisture pushes in warmer air raising snow levels to around 6000-7000 feet. Strong valley inversions across northwest Montana could create conditions favorable for patchy freezing rain by Saturday morning. The latest guidance is showing a 10-30% chance of freezing rain with the highest probability being around the Libby/Troy/Yaak region. A cold front is expected to push through the region on Saturday night into Sunday. This front will drop snow levels down to around 4000 feet by Sunday morning. The lingering trough of low pressure should continue to lower the snow levels down to valley floors by Monday morning. The mountain passes should anticipate a couple of inches of new snow accumulations, along with occasional slick roads Saturday night through Monday morning. && .AVIATION...The ridge of high pressure will strengthen over the next couple of days. Fog and low stratus is in place across many valleys of north central Idaho up into northwest Montana. The fog and stratus will likely erode somewhat each afternoon then increase in coverage and thickness each night. KGPI is impacted by fog/mist currently and is expected to shift to a low stratus cloud deck later this morning. The remainder of the terminals will have the potential for the visibility reductions in localized fog. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$

217 FXUS65 KBOI 031639 AFDBOI Area Forecast Discussion National Weather Service Boise ID 939 AM MST Tue Dec 3 2024 .DISCUSSION...Latest obs and webcams show fog decreasing this morning in the Upper Treasure Valley but continuing in the Lower Treasure Valley. We will end the Dense Fog Advisory at 11 AM MST in the Upper T.V., but keep it going until 2 PM MST in the Lower T.V., then start another Dense Fog Advisory this evening through Wednesday, and likely repeat the process Thursday and Friday. The Air Stagnation Advisory will also be extended through 5 PM MST Saturday. Latest models continue the low-level inversion with air stagnation and areas of fog (dense in the Lower Treasure Valley) through Saturday, but the new deterministic GFS, ECM, and CMC bring in a strong upper trough from the Gulf of Alaska Sunday. The trough should break the inversion as models bring a surface cold front and briefly gusty west winds through the area late Saturday night. The front will be followed by much colder air at higher elevations while mixing out the inversion at low elevations. The mixing will warm the cold valleys and disperse the fog. Models then bring the upper trough in with a chance of snow showers late Sunday/Sunday night, better chance in the GFS than in ECM. After that the models show a new, cleaner, and colder air mass in our area Monday under strong northerly flow aloft, followed by the beginning of another inversion Tuesday. && .AVIATION...Areas of LIFR fog and low stratus at KONO, KEUL, KMAN, KMYL, and KMUO this morning as an inversion remains in place. Some improvement in visibility is expected this afternoon, but low clouds will persist through the day. Tonight, fog and stratus may expand in coverage through the Snake Basin with LIFR conditions, with mountain valley fog also expected. Elsewhere today, it will be clear and VFR. Surface winds: variable less than 5 kt. Winds aloft at 10kft MSL: variable around 5 kt. KBOI...MVFR from mist this morning, with VFR conditions this afternoon. Winds will be light and variable today. 20% chance of IFR/LIFR low stratus or fog moving in this afternoon, increasing to 60% chance after 02z this evening. && .AIR STAGNATION...Mixing heights will stay well below 2000 ft AGL in the valleys through Saturday. Winds should continue 5 mph or less and stagnant conditions will allow air pollutants to accumulate. Increasing confidence (>50% chance) in a trough arriving Sunday being strong enough to scour the inversion and clear out the stagnant air. && .PREV DISCUSSION... SHORT TERM...Today through Thursday night...The surface-based inversion remains, and will be with us through the short term period. A weak upper level trough is expected to come through Thursday night, but it will bring nothing more than some high clouds. Winds will remain light for most folks, and low clouds/fog will likely remain in and near where it was Monday. There will be little change in temperatures, but the diurnal range in areas with low clouds and/or fog will become reduced - lowering daytime highs and potentially slightly increasing overnight lows. The ridge aloft that is bringing the inversion is forecast to reach maximum intensity Wed into Thu, resulting in the warmest temperatures in the mountains. With all that said, changes in the short term part of the forecast were minor. Both the Dense Fog Advisory and the Air Stagnation Advisory will continue as issued. LONG TERM...Friday through Tuesday...The upper ridge is expected to weaken Friday and especially Saturday in advance of an upper level trough forecast to move in Sunday or Sunday night. This feature has better model agreement this morning compared to yesterday, although the exact strength and timing are still uncertain. This system, if it comes through as presently depicted in the latest operational runs, would push a strong- enough cold front through the region Sun/Mon. And this front appears to be strong enough to (at least temporarily) end the inversion. It is also strong enough to warrant a good chance of precipitation, especially in the north (40-70%, with 15-40% across the south), Saturday and Sunday. These precipitation chances decrease Monday to 15-30% (across the north) and then become too low to mention Tuesday, with even lower chances in the south. Temps will remain inverted Friday, perhaps a little less so Saturday, and should return to a more normal pattern Sunday through Tuesday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Air Stagnation Advisory until 9 PM MST Friday IDZ011>014-016-028-033. Dense Fog Advisory until 11 AM MST this morning IDZ012-014. OR...Air Stagnation Advisory until 9 PM MST /8 PM PST/ Friday ORZ061>064. Dense Fog Advisory until 11 AM MST this morning ORZ064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...LC AVIATION.....ST AIR STAGNATION...LC/SP SHORT TERM...SP LONG TERM....SP

779 FXUS65 KLKN 031031 AFDLKN Area Forecast Discussion National Weather Service Elko NV 231 AM PST Tue Dec 3 2024 .SYNOPSIS...High pressure overhead will promote continued warm and dry conditions with above average high temperatures through Saturday before a cold front attempts to slip southward across the Silver State Saturday night into Sunday. && .SHORT TERM...Tuesday through Wednesday night Nearly a carbon copy forecast today across northern and central Nevada with high pressure remaining dominant in the larger-scale Rex block over the western CONUS. Highs this afternoon look to top off in the low 50s for most of the region, likely a degree or two warmer than yesterday as the center of the upper high shifts slight further south and east out of the Pacific Northwest. Highs in and around the inversion level will remain tricky, however, with persistent fog and freezing fog in the Black Rock Desert in southwestern Humboldt County not being represented well in HREF members. Similar conditions forecast for Wednesday with the high continuing its slow progression south and east towards northern Nevada. HREF guidance continues the strong inversion fog in the Black Rock Desert through Wednesday night with weak surface and low-level winds hindering any mixing. Highs across the region will favor the low to mid 50s once again. .LONG TERM...Thursday through next Tuesday Continued upper level ridging to end the week will result in temperatures 10-15 degrees above normal on Thursday, Friday and Saturday. No precipitation will be present during this time, and winds remain below 10mph. Saturday night into Sunday, an upper level trough begins its passage across the forecast area. While long term cluster and ensemble analysis puts the trough axis to the east, it will still be close enough to impact the forecast area. Elko county will experience some slightly stronger winds (15 mph) and scattered precipitation chances (30% or less) on Sunday and Monday. More broadly, the entire forecast area will see temperatures drop to near normal on Sunday and remain there to start next week. && .AVIATION...VFR conditions are expected at all terminals for the next 24 hours. Winds will be generally light, around 10KT or less. FEW to SCT upper and mid-level clouds will also be present with cloud bases around 15,000 feet. && .LKN Watches/Warnings/Advisories... None. && $$ 84/94/92