FXUS66 KOTX 231142 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 342 AM PST Sat Nov 23 2024 .SYNOPSIS... The weekend into early next week will feature seasonably cool temperatures and chances for valley rain and brief snow and periods of mountain snow. Moderate rain amounts for portions of eastern Washington and the Idaho Panhandle will lead to the threat of rock and mud slides near steep terrain. && .DISCUSSION... Saturday through Monday: An unsettled weather pattern will persist over the Inland NW as an area of low pressure continues to spin along the WA Coast slinging disturbances inland. The remnants of Friday's front remains draped over southeastern WA and North Idaho this morning. This front will begin to slowly drift east through the day but not before delivering light to moderate QPF for locations from Lookout Pass to the Blue Mountains and points south. Meanwhile the air mass aloft is cooling with precipitation likely to transition back to snow for elevations above 3000 feet. This includes Lookout Pass within the Central Panhandle Mountains, Blue Mountains, and higher benches of the Camas Prairie. If you are traveling Saturday morning in these areas, be prepared for variable conditions and return to winter driving conditions in the next few hours. Additional QPF amounts of a quarter to half an inch are expected through the afternoon. Using a conservative 10:1 ratio, Lookout Pass has a 50% for 4" or more with the most likely range between 3 to 6 inches. Lower snow levels will be slower to arrive in Winchester which is calling for around of an inch or so. There is a 10-30% chance for lighter showers to build westward into Central and Eastern WA with minimal QPF amounts. A lot of this activity could be more in the form of drizzle with an abundance of low clouds now in place following Friday's rain. The consistent rain over SE WA and NC Idaho will continue to bring a threat for rock-slides. There were two confirmed on Friday in NC Idaho. Unfortunately, its near impossible to determine exactly where these may occur. Flood advisory remains in effect for the Gwen Burn scar for this threat given its sensitive nature to even light precipitation. On Sunday into Monday, a weak but more organized frontal system will pass through with light rain and mountain snow. Thinking many communities will escape Sunday morning and early afternoon precipitation free with shortwave ridging coming through ahead of the system then precipitation will start in the Cascades Sunday afternoon and expand eastward Sunday evening into Monday morning. Snow levels will start off lower with an increased threat for light snow in the Cascade mountains, upper river valleys, and into the Okanogan Highlands. NBM has a 40% chance for at least 4" of snow at Stevens Pass with the most likely range from 3 to 6 inches. It will be a challenging forecast for precipitation type for the lowlands in the Cascade Valleys down toward the Columbia River and into Ferry County. Deterministic models indicate the layer is cold enough for snow with moderate to high confidence for 850mb temperatures below 0C and 0-4km wetbulb temperatures below 0C. However, models may be struggling with how the low stratus will evolve over the next 36 hours which could act to trap afternoon warmth and keep surface temperatures 32-35F. Needless to say, snow is in the forecast but amounts which could vary from a trace to 4 inches come with low confidence. Travelers should be prepared for snowy travel over Stevens, Loup Loup, and Sherman Passes; 30-40% chance for light snow in the aforementioned lowlands. As the system tracks east Monday morning, light snow will be possible down to the valley floors along and north of Hwy 2 into Northeastern WA and North Idaho. This also comes with low confidence for meaningful accumulations given earlier reasoning stated above with low stratus. Probabilities remain around 20-30% for an 1". Anything falling early Monday morning would be of more concern for slick travel vs after 10AM which is more likely to melt on pavement surfaces given the light nature of this event. The next few days will bring areas of fog and low clouds with periodic drizzle when rain or snow is not falling. Fog could be dense at times producing visibility of 1/4 mile or less. Temperatures will vary from the 30s and 40s in the afternoon to upper 20s to 30s at night. Many areas may be getting close or just below the freezing mark so be cautious of black ice. /sb Tuesday through Friday: Tuesday, an upper-level low will move southeast, reaching the OR/CA border. Precipitation chances will decrease, mainly affecting the Cascades and eastern WA. Temperatures will be warmest on Tuesday, with highs hovering around 40. A cool northwesterly flow will develop for the second half of the week, as a high pressure ridge strengthens offshore. Temperatures will drop, with highs in the 30s and lows in the teens to 20s. Precipitation uncertainty remains due to varying model predictions about the ridge's position. If the ridge is near the coast, disturbances will likely miss eastern WA and ID. If it remains further offshore, more precipitation could occur. Precip chances for the Cascades, ID Panhandle, and eastern WA are currently forecast at 20-50% but may change as we get closer and models dial in better. /KM && .AVIATION... 12Z TAFS: MVFR to IFR conditions continue over SE WA and N ID where persistent rains are falling. The rains and a light breeze are keeping visibilities elevated and latest forecast has backed off on the lower visibility due to rain continuing. Further west, a second band of showers is taking aim at the Cascades with a 30% chance to reach Wenatchee. Moses Lake is in between and carries a slightly high risk for cigs/vis to lower with patchy fog. Rain will taper off to showers 18-21z but very moisture boundary layer conditions with steady upsloping winds is likely to produce low ceilings. Drier and cooler air aloft and a modest increase in post- frontal winds should lead to improvements between 18-00z Saturday as the Inland Northwest finally dries out though the push is weak and return of fog or low stratus is expected. The next warm front approaching after 08z will lead to lowering cigs in the Cascades and Wenatchee with light rain/snow developing around 12z. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is low confidence in hour by hour forecast due to saturated conditions within the lowest 2000 feet. Trends this TAF package were toward the LAMP MOS in the near term and HREF probabilities for cigs below 1000 feet Saturday evening and night though the forecast comes with low confidence given differing outcomes for the next 6-18 hours amongst model output. /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 42 33 42 31 39 30 / 80 20 20 20 50 30 Coeur d'Alene 41 33 41 29 36 31 / 100 40 20 20 50 50 Pullman 41 32 42 31 40 31 / 100 40 10 10 40 40 Lewiston 47 33 47 31 43 36 / 100 30 10 10 20 30 Colville 42 31 39 30 35 24 / 50 10 20 40 60 30 Sandpoint 37 30 37 27 34 29 / 90 60 40 30 60 60 Kellogg 38 33 39 25 36 32 / 100 60 30 20 70 60 Moses Lake 45 32 44 35 41 30 / 20 0 20 30 30 20 Wenatchee 40 30 38 33 38 31 / 10 0 30 40 20 20 Omak 39 30 39 34 38 29 / 10 0 40 60 20 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$