136 FXUS66 KOTX 062348 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 348 PM PST Sun Nov 6 2022 .SYNOPSIS.... Snow will spread eastward into Idaho tonight into Monday morning impacting the morning commute. Brisk north winds with cold wind chills on Tuesday. Cold temperatures with lows down into the single digits and teens will continue through the work week before slowly moderating next weekend. && .DISCUSSION... Tonight through Monday: Snow is well underway across north-central Washington where current snowfall reports are ranging from 7 inches to over a foot of snow across the Methow and Okanogan Valleys. A deep upper level low pressure slowly sliding down the BC coast is providing deep southwesterly to southerly flow aloft. An area of strong isentropic lift is supporting the heavy snowfall that is observed in these areas. As expected, this has proven to be a very tricky forecast as temperatures above freezing given the deep southerly flow aloft for the Wenatchee area through the Spokane area and south and up into the Idaho Panhandle. Areas that have been under the heavy snow all morning have seen little warm up and are sitting at freezing to a couple degrees below freezing. As the deep low slowly progresses southward along the northwest coast, an impulse rotating around the low will move across the Inland Northwest tonight into tomorrow morning. This will bring more precipitation across north-central and precipitation across eastern Washington and the Idaho Panhandle overnight tonight into tomorrow morning. Precipitation looks to begin as rain later this evening for the Columbia Basin, the Spokane area and south but will make a transition to snow as an Arctic front begins to push southward across the region. The greatest uncertainty exists for the exact timing of the transition from rain to snow, which would impact the exact snow totals, especially for the I-90 corridor and south. An additional Winter Storm Warning has been issued for Boundary and Bonner counties where snow amounts between 3 to 7 inches are forecasted for Bonners Ferry to Spirit Lake. The NBMv4.1 is giving Sandpoint a 70% chance to see snow totals over 6 inches through tomorrow afternoon. The heaviest snowfall looks to occur between the 4am and 10am timeframe, which will lead to impacts for the Monday morning commute. A Winter Weather Advisory has been issued for the far northern Columbia Basin (Wilbur, Creston) into the Spokane and Coeur d'Alene areas and Shoshone county for tonight through Monday afternoon. Since precipitation looks to begin as rain this evening, the biggest concern for these areas will be for roads to become icy as temperatures cool to below freezing, creating a messy Monday morning commute. Snow totals will be around 2 to 5 inches for these areas. The NBM gives the Spokane area about a 70% chance to see over 2 inches of snow and a 20-40% chance to see over 4 inches of snow. As road temperatures warm above freezing during the day, melting snow and much colder air arriving Monday evening will make for another slippery evening commute especially across untreated roads that were unable to dry during the day. /vmt Tuesday through Saturday: The deepening upper level low will slide south along the west coast Tuesday into Wednesday leaving the Inland Northwest under cold advection from the north and weak warm advection from the south. Mid-high level moisture should exit to the east with the energy from the Monday storm system. However, cloud cover will play a part into our daytime and overnight temperature achievements. The take away message if you stop reading here is temperatures will be bitterly cold through the week ahead with daytime and overnight temperatures around 20 degrees below normal. * Temperatures: Consulting the ensemble models for temperatures, the GEFS has trended colder while the EC ensemble has trended warmer. The climate percentiles for all ensembles are bottoming out for the lowest temperatures at 850mb Tuesday and further remain in the lowest 5th percentile through the week for high temperatures. Comparing to normal which is around 44F for eastern Washington for daytime temps, Tues - Fri will see temperatures around 15-18F colder than normal. The NBM would say there is a 25% chance of seeing daytime temps below 28F through the week for Spokane, Coeur d'Alene, Pullman, Moses Lake, Omak, Wenatchee and 35-50% chance of less than 28F for Deer Park, Sandpoint, Bonners Ferry, Republic. Windchill values will dip into the single digits and even some negative values Tuesday morning and similar but slightly warmer Wednesday morning. * Wind: A surface high develops in British Columbia as the upper Low dives south, resulting in a tighter pressure gradient drapped across Washington and Idaho. Breezy north winds will develop across the Columbia Basin, the Okanogan Valley, and the Purcell Trench. Sustained 12-15 mph with gusts of 20-25 mph will make those cold temperatures even more biting cold. * Snow? Some of the ensemble guidance would suggest low probabilities of seeing a weak disturbance Wednesday rotate around the Low as it tracks into the northern Rockies bring measurable snow to the L-C Valley, the Palouse, the Camas Prairie and central/southern Idaho. NBM has 55% probability of measuring snow at Pullman for Wednesday evening. Elsewhere, it looks like a dry forecast. Next weekend there are signals of seeing a flat ridge settle over the Northwest though models are wildly indecisive at the moment. /Dewey && .AVIATION... 00Z TAFS: Snow is continuing across the Methow Valley and Okanogan Valley and is expected to continue through the night. Precipitation will spread east this evening and become heavier overnight for GEG, SFF, COE, SZT, PUW. Precipitation looks to begin as rain or a rain/snow mix for the I-90 corridor and south with a transition to snow overnight. Marginal VFR and IFR conditions will be possible after 9z through Monday morning. Winds will be breezy from the east- northeast for GEG, SFF, COE, OMK, and from the east- southeast for MWH, PUW, LWS. vmt && .PRELIMINARY POINT TEMPS/POPS... Spokane 25 30 15 30 13 30 / 90 70 0 0 10 20 Coeur d'Alene 24 29 13 31 14 30 / 80 90 0 0 10 20 Pullman 31 39 21 35 18 27 / 70 60 0 0 20 20 Lewiston 36 44 26 38 26 34 / 60 60 0 0 20 30 Colville 23 29 10 32 4 33 / 90 70 0 0 10 10 Sandpoint 22 24 12 27 13 28 / 70 90 0 0 10 20 Kellogg 24 30 11 30 13 29 / 70 90 0 0 10 20 Moses Lake 30 40 23 34 17 32 / 70 30 20 10 10 10 Wenatchee 29 34 24 32 18 32 / 80 40 50 10 10 10 Omak 28 33 18 35 14 34 / 90 70 20 10 10 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Winter Storm Warning from 1 AM to 4 PM PST Monday for Northern Panhandle. Winter Weather Advisory from 1 AM to 4 PM PST Monday for Central Panhandle Mountains-Coeur d'Alene Area. WA...Winter Weather Advisory from 1 AM to 4 PM PST Monday for Spokane Area-Upper Columbia Basin. Winter Storm Warning until 10 AM PST Monday for Northeast Mountains-Okanogan Highlands-Okanogan Valley-Waterville Plateau-Western Okanogan County. Winter Weather Advisory until 10 PM PST this evening for Central Chelan County-Wenatchee Area-Western Chelan County. && $$