678 FXUS66 KOTX 302224 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 224 PM PST Thu Jan 30 2020 .SYNOPSIS... Another round of light valley rain and moderate accumulating mountain snow will arrive tonight. Temperatures Friday and Saturday will be well above average with many locations climbing into the upper 40s and 50s. The passage of a strong cold front on Saturday may produce strong gusty winds across the Columbia Basin, Palouse, and West Plains. A cooler weather pattern is expected next week with a risk more low elevation snow by Tuesday night into early Wednesday. && .DISCUSSION... Tonight through Saturday night...Satellite this afternoon indicates an atmospheric river cresting over the top of an upper level ridge axis situated over the forecast area. The trough visible over the Gulf of Alaska will release a short wave from it's base tonight which will suppress the ridge and allow the moisture feed to splash the inland northwest once again with another round of mainly valley rain and higher elevation snow...with snow levels starting out a bit lower in the Cascades due to persistent cool air damming against this massif...but rising steadily through tonight. This will be another warm front...however the zonal nature of the moisture feed (not out of the southwest for sustained isentropic nourishment like most of the warm fronts of the last week) will allow a bit of a rain shadow in the deep basin and Cascades lee with another quarter to 1/2 inch of precipitation falling mostly over the Idaho Panhandle and the rising terrain of the eastern basin tonight and Friday before the moisture feed once again gets directed north of the region into Canada. The region will then exist solidly in the warm sector of this system for 18 to 24 hours or so with snow levels way up in the 7000 to 8000 foot range for much of Friday and Friday night. For the populated lower elevations this will be a showery or possibly even dry period with breezy and mild conditions with Friday highs in the upper 40s to mid 50s and many locations not dropping below the mid 40s overnight into Saturday morning. ...Strong Winds Possible on Saturday... Unfortunately it appears we will have to pay the piper for this temperate interlude on Saturday. Models are coming into agreement in ejecting the Gulf of Alaska trough into Canada on Saturday...which will promote a deep surface low pressure tracking through British Columbia and Alberta. The pressure gradient alone from this passing low pressure will promote windy conditions across the region...probably in the Wind Advisory category of 25 to 35 mph...but the low pressure will also drag a strong cold front through the forecast area as well. Previous case histories of similar set-ups have featured very strong wind gusts surfacing just ahead of and along strong cold front as a pre- frontal low level jet is drawn down to the surface in a more or less random hit-and-miss fashion. The highest threat for this possibility is the exposed terrain over the rising eastern basin...with ridge tops in the surrounding mountains also subject to strong winds but the deeper valleys largely shielded. This potential is not a sure bet yet with only a few hi-res models picking up on this potential...however there is enough confidence to warrant a High Wind Watch on Saturday for those zones which appear most susceptable to this threat. Showers will also inhabit the frontal interface as it passes any particular location...and snow levels will quickly lower but a solid precipitation shadow will develop over the basin in the front's wake with further precipitation...increasingly snow with moderate accumulations limited mainly to the Idaho Panhandle mountains and the high Cascades near the crest. /Fugazzi ...Snow risk returns to valleys Tuesday night and early Wednesday... Sunday to Thursday: The Inland Northwest cools to more seasonal temperatures, with a few opportunities for precipitation including snow down the valley floors. First Sunday and Sunday night an unstable upper trough continues to migrate across the region, with embedded shortwave energy. Lapse rates average around 8.5 C/km in the 850-500mb layer and mixing remains good. Yet a fair amount of dry air comes in with PWATs dropping to around 0.10 inches. Normally the unstable upper trough and the features moving by would be enough to make me think of an isolated hit-and- miss shower potential. Yet the amount of drying that occurs makes me more hesitant in this situation. So the main precipitation threat will be around the mountains, with more limited chances around the eastern third of WA and lower elevations ID. So there is some risk outside of the mountains, but the threat is low. The overall threat will wane through the later evening into the overnight. Winds will remain breezy but should be much lighter than Saturday, with speeds of 10-15 mph and gusts to 20 mph, with higher gusts in the mountain peaks. Then from Monday to Thursday the area is dominated by northwest flow, which will carry in the next moderate threat of snow over a broader area. Monday and at least a portion of Tuesday looks mostly dry. A weak impulse crossing near the Panhandle and the aforementioned flow keeps some snow shower threat alive around the central Panhandle mountains Monday, but amounts look limited if any. Then the approach of the next wetter and organized system Tuesday brings snow chances coming over the Cascades, largely in the afternoon. Chances start to rise over the remainder of the area in the afternoon too, with risk the highest at this point sometime between Tuesday evening and mid-Wednesday. The precise details of this system have low confidence this far out in the forecast. Yet the system at this point carries in some modest moisture (with PWATs around 0.35 to 0.70 inches), with 850 temperatures well below zero through early Wednesday and a mean west-northwest flow. This would favor the highest threat of precipitation over mountain zones and southeast CWA, with secondary threat over northeast WA and the lowest threat in the lee of the Cascades and deeper Columbia Basin. Current timing would favor the predominant precipitation type as snow. So this has the potential for bring at least a few inches of snow and potentially more moderate to heavy amounts, especially in the mountains. So there is still winter weather to contend with. By later Wednesday into Thursday some milder air start to nose in as the warm front lifts further east and northeast. The atmosphere remains moist as well. This will keep precipitation chances going, though with the highest risk pushing toward the mountain zones. With milder air the precipitation is expected to be more of valley rain or rain/snow mix with mountain snow. Exceptions could the northern mountain valleys, from the Okanogan Valley to the northern Panhandle, where precipitation may remain more in the form of snow until later Thursday morning to afternoon. /Cote' && .AVIATION... 18Z TAFS: A moist boundary layer capped by a strong inversion at around 3000 feet MSL will promote areas of IFR and LIFR conditions in fog and stratus mainly over the western and northern Columbia Basin today where southeasterly winds will push the deepest low level moisture. The KMWH TAF site will be very slow to improve under these conditions and will probably remain under IFR ceilings through the next 24 hours. KEAT will probably deteriorate to MVFR or IFR conditions this afternoon as the gradient pushes this stratus into the area. The KPUW TAF site will benefit from this southeast wind for VFR conditions and the KLWS TAF site will slowly improve today with. Satellite suggest the KGEG TAF site will deteriorate again by 20Z to MVFR or possibly IFR conditions as the winds push another area of upslope stratus into the TAF site with shreds of this stratus affecting KSFF as well. The next moist Pacific storm system will spread -RA west to east across the forecast area this evening and tonight. /MJF && .PRELIMINARY POINT TEMPS/POPS... Spokane 37 51 44 52 29 39 / 70 60 10 50 30 20 Coeur d'Alene 34 47 41 49 28 37 / 80 90 20 70 40 20 Pullman 37 51 41 50 29 38 / 70 70 0 40 40 20 Lewiston 41 55 44 56 34 43 / 50 30 0 30 40 20 Colville 33 46 38 50 25 39 / 40 60 40 60 30 20 Sandpoint 33 44 41 45 27 35 / 80 100 50 90 50 30 Kellogg 33 44 40 46 26 36 / 80 100 30 70 80 40 Moses Lake 35 56 44 57 29 44 / 30 10 0 20 10 10 Wenatchee 33 46 38 49 27 38 / 30 50 10 50 10 10 Omak 33 42 39 48 25 36 / 30 50 20 50 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...High Wind Watch from Saturday morning through Saturday afternoon for Coeur d'Alene Area-Idaho Palouse. WA...High Wind Watch from Saturday morning through Saturday afternoon for Lower Garfield and Asotin Counties-Spokane Area- Washington Palouse. && $$