Area Forecast Discussion
Issued by NWS Spokane, WA

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000 FXUS66 KOTX 151257 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 457 AM PST Thu Nov 15 2018 .SYNOPSIS... Mainly mountain showers will continue today. A cold front will bring more widespread rain and snow tonight into Friday, with colder temperatures and locally breezy winds behind the front. Cool and dry weather will persist through the weekend into early next week. && .DISCUSSION... Today through Saturday: Mainly fair weather persists across the Inland Northwest under northwesterly flow aloft. Doppler radar imagery is showing a few isolated orographic showers in Shoshone County ID. High clouds passing overhead are restricting the formation of dense fog formation this morning, but patchy fog is certainly possible in the Northern Valleys down into Spokane and could pose a travel nuisance in the morning. Forecast soundings suggest that low stratus could stick around in the Valleys and down into the Columbia River Basin, which may keep high temperatures suppressed this afternoon. A cold front dropping south out of Canada will then begin to bring unsettled weather across much of the region starting tonight. This system isn`t particularly moist, with precipitable water values expected to remain below 0.75". As such, expect light precipitation totals with this system: generally less than 0.10" across the Valleys, and perhaps a few tenths of liquid equivalent precipitation over the mountains. Snow levels will lower rapidly as precipitation begins to taper off: an inch or two of snowfall will be possible at Lookout Pass, and a few inches possible over the higher ID mountains. Locally breezy north winds will begin to develop behind the cold front on Friday, mainly through the Okanogan Valley and Purcell Trench. These winds may continue into early Saturday. Cold advection will also usher in a cool Canadian airmass: temperatures over the weekend will be characterized by cold nights and mostly clear but cool days. Dang Sunday through Wednesday: Dry weather continues early this week, though with some fog potential, before a more progressive pattern and some threat of precipitation attempts to move in midweek on. Models show rising 500mb heights into Monday and the bulk of the moisture in the flow pattern is shallow, either skulking near the surface or spilling over the top of the ridge aloft. All this supports dry weather but boundary layer moisture under inversions will carry a late night/morning fog potential. Confidence is coverage and persistence is only fair, but the best threat will be in the sheltered north valleys and secondarily out across the deeper Columbia Basin. Temperatures will be held back under this pattern, with some areas not getting out of the 30s or lower 40s in the afternoon. Between Monday night and Wednesday models suggest high pressure starts breaking down, with somewhat deeper moisture and energy starting in from the Pacific. However the details are hazy as model disagreement persists, with some solutions quicker to bring that moisture in than others. Through early Tuesday the odds favor it remaining dry, though the ensemble models still bring a threat into the Cascades. Then between later Tuesday into Wednesday, continuing into next Thursday, the threat starts increasing region-wide. At this point nothing shouts that the risk will bring large impacts as the first system into a ridge does tend to be weaker. Still snow levels are still looking to be near to slightly below pass level during the day and closer to some valley floors at night. This could mean some impacts to Thanksgiving travel over the passes. However it may be that any real impacts may hold off until the return trip. Overall temperatures look near to slightly below normal and outside of the mountain peaks, winds look relatively light. /Cote` .AVIATION... 12Z: Low clouds continue across the lower Columbia Basin, bringing IFR conditions to KEAT to just south of KMWH. Low confidence in how much of that will break apart today. Low clouds have begun to form in the northern valleys early this morning, and may bring MVFR/IFR ceilings to KGEG-KSFF-KCOE for much of the day. A weak weather system is likely to bring -SHRA to KGEG-KSFF-KCOE after 06z Friday. Dang && .PRELIMINARY POINT TEMPS/POPS... Spokane 43 33 42 25 39 23 / 0 30 20 0 0 0 Coeur d`Alene 44 34 43 24 40 24 / 10 40 30 0 0 0 Pullman 49 33 45 27 42 24 / 0 30 40 0 0 0 Lewiston 54 38 50 32 47 28 / 0 20 40 10 0 0 Colville 42 31 45 23 43 22 / 10 40 10 0 0 0 Sandpoint 42 33 42 22 38 23 / 20 60 20 0 0 0 Kellogg 44 34 41 23 38 25 / 20 50 50 10 0 0 Moses Lake 45 32 48 25 44 21 / 0 10 10 0 0 0 Wenatchee 46 37 47 30 44 28 / 0 10 30 10 0 0 Omak 44 32 48 25 44 23 / 0 30 20 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$

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