834 FXUS66 KOTX 142249 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 249 PM PST Thu Feb 14 2019 .SYNOPSIS... Another round of precipitation will transit the region tonight. Snow amounts will be generally less than previous storms but the snow will be wetter and slushier on road ways for the morning commute. There will be a threat of pockets of freezing rain for this evening's commute in the eastern Columbia basin. Unsettled weather continues for Friday and through the weekend with light snow likely. Colder weather returns early next week with unsettled conditions remaining. && .DISCUSSION... Tonight...The Pacific satellite loop reveals a double barrel troffy structure off the coast...with the next in a seemingly endless series of cold polar closed lows dropping down out of the Gulf of Alaska...with this new low becoming dominant as it kicks the previous low inland into northern California as a negatively tilted trough. The net result is deep southerly flow over the region with a series of embedded fronts and waves riding south to north into and eventually through the forecast area. The main issue for tonight is apparent on regional radar as a moist warm front enhancing moisture into a field of light isentropic precipitation which will overspread the entire region tonight. For the most part this precipitation will be snow...heavy accumulations in the deep basin and Waterville Plateau...much of which has already fallen during the last 6 hours but expected to linger into the evening before the frontal band moves north and allows a tapering to simply occasional light periods. The northern basin zones including the Spokane/CDA area will imminently begin snowing with up to an inch or so expected on the roads for the evening commute...but there may be some mixing with rain late this afternoon and early evening making for a slushy commute. This actually is the main uncertainty in the forecast. The warm front can be expected to push some warmer air aloft into the area this evening...but all models suggest a weak meso-low developing over southeastern Washington this evening which may very well retard and eventually stop the northward progression of the rain/snow line. Along this interface generally along I-90 from Ritzville to Spokane there may be a few pockets of freezing rain but current temperatures across this region suggest this threat is very low and transitory...and road surface temperatures around the region have risen well above freezing this afternoon due to longer daylight and higher sun angles so travel impacts from freezing rain are expected to be minimal...with the potential for grippy slush being the main road surface issue for the evening commute. The Palouse and points southward are solidly in the warm sector of this storm...with current rain expected to stay rain until later tonight. Overnight tonight the warm front will stall and drift back south allowing cold air to once again turn all precipitation back to snow. but further basin accumulations will be on the light side but with heavier water content compared to what we have become accustomed to in the last week. North of the basin all snow continuing through the night is a safe bet...with another 3 to 5 inches in the northern valleys tonight through Friday morning. The current suite of Winter Weather Advisories will be expanded to cover the northern mountains through tonight and the Coeur D'Alene area through this evening...as well as the Central Idaho Panhandle Mountains which will see another sustained period of upslope flow supported snow showers for tonight through Friday. /Fugazzi Friday and Saturday...The slow moving offshore low will make drift east-southeast during this period leaving unsettled southwest upper level flow over the region. Meanwhile a couple of shortwave disturbances will be embedded in this southwest flow and should be able to trigger a variable amount of snow showers on Friday. The first shortwave will track through eastern Washington and north Idaho during the morning with a weaker one tracking into SE Washington and NC Idaho in the afternoon and evening. The first one will trigger a good chance of showers but precipitation amounts will be fairly light. The second one will be even lighter. Unlike today where there is a warm wedge of air above the ground leading to complex precipitation determinations, tomorrows should be much more straight forward. In other words anything which falls will fall as snow. Most of the snow amounts for tomorrow will be an inch or less, with locally heavier amounts over the Idaho Panhandle where orographic ascent associated with 850 mb winds out of the southwest will likely enhance totals. The winter weather advisories which have been issued for NE Washington and north Idaho will continue into tomorrow as a result but things will generally wind down in the afternoon. By Friday night and Saturday the weather will dry out a bit for most folks as the upper level low shears out as it drifts toward northern California. Even though most of the energy with the low will be dropping well south of our region there are still some vestiges of the upper level trough this far north which should prolong the chance of showers, especially over north Idaho. Again the precipitation amounts should be light, but on and off showers may continue through much of this period. Sunday and Monday The more exciting weather is expected to arrive on Sunday as arctic air is once again set on paying us a visit. Model guidance has been consistent on bringing this colder surge of air into the Okanogan Valley by midday Sunday and a little later down the Purcell Trench. Light snow will be possible ahead of this feature, however the bigger story will be a return of brisk winds and much colder temperatures. Most of the winds will occur from late Sunday morning and persist into the evening. Sustained speeds of 20-30 mph will be possible in the aforementioned areas and areas of blowing snow will be possible from the Okanogan Valley and onto the Waterville Plateau. This event should be a far cry from the last blizzard like event since we don’t expect to see a significant amount of snow. Nonetheless the snow in that area likely won’t crust over from melting or rain so blowing will be a distinct possibility. The winds will also usher in much colder temperatures with lows dipping into the single digits and highs only in the upper teens and 20s. With the winds in the mix, Wind chill values once again will dip below zero with the coldest readings expected in the Okanogan Valley and Waterville Plateau through Monday morning. Outside of that area the chill values won’t be as cold but they will be far from pleasant. Unlike the last arctic push, the winds with this system won’t last long with most of the model solutions showing a rapid decrease in pressure gradients by Monday afternoon or evening. fx Tuesday into early Friday... The snowy pattern will continue into the middle of next week as waves from the northwest move in. At this moment, the models are not showing it to be warm enough to support rain, so this cold air will likely bring any precipitation as snow. The models suggest the heavier precipitation will occur in the Cascades, southeastern Washington, and lower Idaho Panhandle on Wednesday. The precipitation's arrival in the Palouse and Lewiston will arrive with below and/or mid-30s temperatures most likely bringing their precipitation in the form of snow. There is high confidence in cold temperatures with below normal temperatures throughout the region. However, models are really beginning to differ further into the week on Thursday and Friday. The European and Canadian are favoring a much deeper trough with a drier atmosphere and the continuation of cold, below normal temperatures. However, the GFS shows the flattening of the trough with more moisture and possible precipitation. At this moment, the models are showing low winds and gusts in the northern Washington valleys and north Idaho Panhandle on Thursday, but with this northerly flow, there is the potential for stronger winds in these locations. Still time for these factors to change as models begin to better align. JS && .AVIATION... 18Z TAFs: A warm front running west to east over northern Oregon at 18Z will move north through the region today spreading precipitation to all TAF sites. Precipitation at KLWS and KPUW will likely be -RA with MVFR cigs. At KEAT upslope flow into the nearby Cascades will persist through today and probably until around 03Z-06Z Friday for a long run period of -SN with accumulations of 4-6 inches of dry snow in IFR and occasional LIFR cigs and vis at the TAF site. KMWH is also likely to stay in the -SN area but with the possibility of some -FZRA mixed from 00Z to 04Z with IFR conditions remaining through the TAF period. The KGEG/KSFF and KCOE TAF sites will be subject to initial snow today but depending on how far north the warm sector reaches may see a period of -FZRA between 00Z and 03Z before turning back to snow overnight with 1 to 2 inches of accumulation. MVFR and IFR ceilings and vis will be common at these sites after conditions begin to deteriorate after 21Z today. /MJF && .PRELIMINARY POINT TEMPS/POPS... Spokane 26 32 24 31 22 28 / 80 50 20 10 20 20 Coeur d'Alene 28 34 26 33 22 28 / 80 70 30 20 30 30 Pullman 29 34 23 33 21 28 / 70 70 20 20 20 30 Lewiston 35 40 28 39 27 33 / 50 60 10 20 20 20 Colville 26 35 24 35 20 30 / 80 70 30 20 30 20 Sandpoint 30 34 29 34 24 27 / 90 70 50 40 40 30 Kellogg 31 35 29 34 23 28 / 90 90 50 60 40 40 Moses Lake 22 33 21 32 21 29 / 70 40 0 0 10 10 Wenatchee 23 33 22 33 21 29 / 70 40 10 10 10 10 Omak 24 32 24 33 20 27 / 80 50 10 10 20 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Winter Weather Advisory until 10 AM PST Friday for Northern Panhandle. Winter Weather Advisory until 10 PM PST this evening for Coeur d'Alene Area. Winter Weather Advisory until 4 PM PST Friday for Central Panhandle Mountains. WA...Winter Weather Advisory until 10 AM PST Friday for Northeast Mountains-Okanogan Highlands. Winter Weather Advisory until 10 PM PST this evening for Spokane Area-Washington Palouse. Winter Weather Advisory until 10 PM PST this evening for Moses Lake Area-Upper Columbia Basin. Winter Storm Warning until 4 AM PST Friday for Waterville Plateau-Wenatchee Area. Winter Weather Advisory until 4 AM PST Friday for East Slopes Northern Cascades. Winter Weather Advisory until 4 AM PST Friday for Okanogan Valley. && $$