FXUS66 KOTX 141804 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1004 AM PST Sat Dec 14 2024 .SYNOPSIS... Rain and snow will move out of northeast Washington and north Idaho this morning. This afternoon will be mild and locally breezy with afternoon temperatures climbing into the upper 30s and 40s. Sunshine is expected across much of central and eastern Washington on Sunday, but the sun won't last long. On Monday a swath of light snow will spread across the Inland Northwest. Tuesday through the weekend will feature temperatures in the 30s and 40s with precipitation mainly confined to the mountainous terrain. && .DISCUSSION... Quick update this morning to extend the winter weather advisory for the Stevens Pass area until 6am Sunday. Snow accumulations through the day will be light, with about an inch or two expected. Once the sun sets and the cold front goes through, they will be able to accumulate snow more efficiently, with an additional 4 to 7 inches expected overnight. && .PREV DISCUSSION... /issued 453 AM PST Sat Dec 14 2024/ Today and Tonight: Warm frontal precipitation will exit northeast Washington and north Idaho by mid morning. As rain and snow exit, south winds will increase across central and eastern Washington. Sustained winds of 10 to 15 mph will be common across the Columbia Basin, West Plains, Waterville Plateau, and Okanogan Valley. Gusts in excess of 20 mph are forecast by the High Resolution Ensemble Forecast (HREF) for Ritzville, Davenport, and Wilbur late this morning through the afternoon. The mild south winds will scrub any fog from the Columbia Basin and push temperatures into the upper 30s and 40s. There will be a resurgence of precipitation along the Cascade Crest this afternoon and evening as the cold with this system moves through western Washington. By the evening, the cold front will interact with moisture streaming into southeast Washington and the Idaho Panhandle. As snow levels fall to 3000 feet or less overnight, the mountains of Shoshone county will receive 2 to 4 inches of new accumulation. Sunday: The passage of a cold upper trough on Sunday will generate mountain snow showers over the Cascades in the morning and the peaks of north Idaho through the day. Breezy west winds across the Columbia Basin and Palouse will help to keep the low levels mixed. Morning stratus around Pullman and Spokane should lift by mid day. The National Blend of Models (NBM) continues to advertise partly to mostly sunny skies across central and most of northeast Washington Sunday afternoon. Mostly clear skies in the evening will allow temperatures to fall into the 20s and low 30s before clouds spread over the region ahead of Monday's system. Monday: There is good agreement that light snow will spread east of the Washington Cascades Monday morning and reach north Idaho by mid day. A swath of 1 to 2 inch accumulation is anticipated across central and eastern Washington along and north of Interstate 90. Temperatures in the low to mid 30s around Moses Lake, Washtucna, Pullman, and Lewiston will have the potential to limit accumulations, especially for snow that falls during the afternoon. /GKoch Tuesday through Friday: Confidence wanes in the overall weather pattern for Tuesday through Thursday as differences emerge among the global ensembles. While nearly all the ensembles agree on an upper level ridge shifting over the western US, there is significant disagreement on how far north it will extend. Many of the ECMWF ensembles and the deterministic members keep southwest flow into the Pacific Northwest, allowing moisture and precipitation to persist into Tuesday. Meanwhile, the deterministic GFS has a larger amplitude ridge over the region with dry weather on Tuesday. The GFS ensembles, however, aren’t as convinced with a handful of members aligning closer with the deterministic ECMWF and its ensembles. For Wednesday and Thursday, models are showing another wave moving into northwestern Washington or southwestern Canada, but there are significant differences in the overall timing and exact placement. This will be a period to monitor for another shot at moderate snowfall amounts for the Cascade valleys, especially for the Methow Valley. The forecast trends drier, although cloudy, for far eastern Washington and north Idaho late Thursday into Friday with better agreement on the placement of the ridge axis centered over north Idaho and western Montana during this timeframe. This would keep the door open for moist, southwest flow into the western slopes of the Cascades where precipitation chances persist for the Cascade crest through the entire period. /vmt && .AVIATION... 18Z TAFS: Low ceilings have dispersed for Pullman, Spokane, Coeur d'Alene as the well mixed warm sector spreads across the Inland Northwest. Unfortunately, stratus remains across central WA and MWH/EAT. Once the winds turn more S/SW in the next few hours, their cigs will improve, and have moderate to high confidence of that occurring. Light rain and snow will redevelop late in the day and into the evening across the Idaho Panhandle and far southeast Washington as the cold front with this system interacts with moisture moving up from Oregon. A 1000-2000ft cloud deck is advertised after 10z around Pullman which will have the potential to spread into Spokane and Coeur d'Alene around 15Z. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Redevelopment of stratus towards sunrise Sunday morning around Pullman, Spokane, and Coeur d'Alene is moderate. It is a common winter occurrence, but ceilings are difficult to predict. With the wind expected 10-15kts overnight at KGEG, this usually means 1500-2500ft. If boundary layer winds end up being less than 10kts, we may be dealing with fog or ceilings below 1000ft. ----------------------- 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 45 29 37 28 34 29 / 10 10 0 10 80 70 Coeur d'Alene 43 30 36 27 33 30 / 10 30 10 10 70 80 Pullman 45 29 37 28 35 29 / 50 50 10 10 80 80 Lewiston 48 34 44 32 38 33 / 30 60 0 0 60 50 Colville 39 24 35 23 33 23 / 10 10 0 20 80 60 Sandpoint 39 30 34 27 33 29 / 30 30 20 20 80 80 Kellogg 42 31 33 28 33 32 / 30 70 50 10 80 90 Moses Lake 45 28 38 30 36 27 / 10 10 0 20 90 40 Wenatchee 39 29 36 29 35 26 / 0 0 0 40 80 30 Omak 40 27 36 25 33 26 / 10 0 0 30 80 30 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Winter Weather Advisory until 6 AM PST Sunday for Western Chelan County. && $$