Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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657 FXUS66 KOTX 141216 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 416 AM PST Thu Nov 14 2024 .SYNOPSIS... Thursday will be unsettled with widely scattered showers and breezy southwest winds. Drier conditions return Friday with areas of morning fog. Fog could be dense Saturday morning. Heavy mountain will return Saturday night and Sunday with another weather system moving through the area. There is a chance of some light lowland snow Sunday morning. Next week looks much drier with high pressure settling in. && .DISCUSSION... Today through Friday night: An elongated upper-level trough will migrate through the region over the next 48 hours. Temperatures aloft at 500 mb are cooling this evening and precipitation is transitioning to more of a convective nature with on and off showers. Showers this morning have been consistent in the Idaho Panhandle, NE WA, and Cascade Crest due to the favored orographic lift and aided by smaller vorticity lobes within the mean trof. The pattern will not change much for today (THU) will be the case through the day on Thursday however rainfall amounts will be more chaotic and generally under a tenth to quarter of an inch. The lowest probabilities for showers today will be in the lower Basin between Ritzville to Wenatchee northward toward Omak given some shadowing from the Cascades yet cannot guarantee a completely dry day given the cooling aloft and steeper lapse rates. Snow levels will remain around 3500-4500 feet. Temperatures this afternoon will remain mild with readings in the 40s to lower 50s along with breezy southwest winds gusting near 25 mph at times. The trough axis will pass through overnight with calming winds and decreasing shower chances. Given the recent rainfall, breaks in the clouds will allow for fog to form rather quickly after dark, some which could become dense. The main uncertainty comes with the amount of clearing with models indicating a plethora of moisture lingering within the 850-700 mb layer east of a line from Republic to Moses Lake. A few light showers will linger over North Idaho, Blue Mountains, and Northeastern WA on Friday but dry air advection will continue under northwest flow aloft. PWATs will dip down near 0.2-0.3". This should allow for more breaks in the clouds and partial sunshine. Temperatures will cool around 5-8 degrees with highs cooling back into the 40s. Friday night will deliver the highest probabilities for clearing skies and light winds. This will bring a favorable setup for fog across the lowlands of the Inland NW. Those with travel plans overnight or early Saturday morning are urged to leave extra time and be prepared for visibility restrictions. Conditions could also be slick with a 70-90% chance for temperatures to cool below freezing by sunrise Saturday morning for just about every site outside of the L-C Valley. /sb Saturday through Monday: Saturday will start off mostly dry under a weak ridge, though mid-to-high clouds will increase as subtropical moisture moves in. By the afternoon and evening, westerlies will strengthen due to an approaching shortwave trough from the Gulf of Alaska and widespread precipitation will form. Lowland Snow: Saturday night will bring a chance for lowland snow, though any accumulation in the Spokane metro is expected to be light and mostly on grassy surfaces, as warmer road temperatures will limit snow accumulations. Once cloud cover settles in on Saturday, surface temperatures will have limited ability to drop, especially with increasing moisture from the subtropical plume. Initially, temperatures at the 850 mb level should support snow in the Spokane/Coeur d`Alene area, but overnight warming will likely turn snow to rain. The best chances for significant snow accumulation are in areas like the northern Pend Oreille River Valley and Priest Lake area, where persistent fog and cooler 850 mb temperatures (around -5C) will keep warming at bay during the day Saturday. Chances for at least 2 inches of snow Saturday night will vary significantly by location: Spokane: 0% Colville: 5% Deer Park: 10% Winthrop: 15% Newport and Sandpoint: 30% Republic: 40% Coolin: 70% Metaline: 80% Mountain snow: Mountain passes and higher elevations could receive over 3 inches of liquid precipitation. With snow ratios expected between 10 to 15 inches per inch of liquid, the mountain passes are likely to see some of the highest snowfall totals of the season. Snow totals will be cut down a bit at Stevens pass overnight into Sunday with strong warm air advection leading to a changeover to rain. Models suggest a convergence zone forming over Stevens Pass on Sunday behind the front passage, with wind gusts reaching up to 40 mph. Snowfall will make travel through the Cascades and Lookout Pass challenging. Chance of snow : 6 12 24 36 Sat PM-Mon PM: ----------------------------------------------- Stevens Pass : 100% 90% 45% 15% Washington Pass: 100% 100% 50% 10% Sherman Pass : 60% 5% 0% 0% Lookout Pass : 100% 70% 15% 0% Monday through Thursday: As this system passes, strong high pressure will build bringing drier conditions. Temperatures will remain in the 30s and 40s, with lows in the teens to upper 20s. This pattern could lead to air stagnation and fog, which will be monitored. /DB && .AVIATION... 12Z TAFS: Breezy south/southwest have maintained VFR ceilings for most terminals along and south of Hwy 2 this morning. North of highway 2, including Omak, Colville, and Sandpoint, MVFR ceilings have become established. HREF has a 30-60% chance for these to expand southward into COE, SFF, GEG, west toward Wilbur between 16-19Z for a few hours. The pattern is also conducive for passing showers as an upper-level trough passes through. Challenging, low confidence forecast overnight with potential for breaks in the clouds to allow for fog to develop given lighter winds and very moist boundary layer conditions but MVFR stratus is more likely coming with 50-80% chance via the latest HREF. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is a variety of outcomes for Thursday night into Friday morning from dense fog to persistent stratus for locations like PUW, COE, GEG, MWH, and EAT. Many areas received appreciable rainfall in the last 24 hours and it will not take much for fog to develop with breaks in the clouds Thursday night. If the stratus can develop between 2000-3000 feet, this would eliminate fog potential with visibility mainly impacted from mist and more likely to fall within the 4-6SM range. /sb ----------------------- 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 48 30 42 27 40 30 / 60 40 30 20 10 80 Coeur d`Alene 45 32 42 29 39 31 / 80 50 40 50 20 80 Pullman 48 32 40 28 40 30 / 60 30 50 50 10 70 Lewiston 55 37 47 33 47 35 / 30 30 40 30 0 50 Colville 44 27 43 21 38 29 / 80 50 40 20 30 90 Sandpoint 41 32 41 28 37 31 / 90 80 60 50 40 90 Kellogg 42 32 41 31 36 31 / 90 50 60 60 40 70 Moses Lake 54 29 46 24 41 34 / 10 10 0 0 10 60 Wenatchee 51 34 48 27 41 34 / 30 20 0 0 10 70 Omak 49 32 46 25 41 31 / 30 20 10 0 20 80 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Winter Storm Warning until 4 PM PST this afternoon for Western Okanogan County. && $$