Springdale, WA 99013 Weather

Key messages

- Valley rain and mountain snow showers through the week.

- Periods of light snow showers on the Cascade passes with minimal accumulations.

- Saturday is looking dry for Central Washington. Light rain chances increase over Idaho and Eastern Washington Saturday evening and night.

Synopsis

Low pressure will remain off the coast through Friday then eject inland over the weekend. Valley rain and mountain snow is forecast at times through the week with periods of light snow impacting the Cascade passes. The incoming system will bring increasing chances for light rain Saturday evening and night across Idaho and eastern third of Washington.

Discussion

Tonight-Thursday: A cold upper-level trough is carving into the Northwest today. A leading shortwave passed through the area today (Wednesday) and was responsible for the more persistent rain and mountain snow showers. This shortwave will eject into BC this evening with the main, and reinforcing low digging southward along 130W just off the WA Coast. This will allow the air mass to slowly moderate from southeast to northwest and shift the main threat for light showers back into the Cascades and northern mountains. Given the warming aloft, shower intensities will be on the decline with minimal additional snow accumulations in the mountains. Overnight temperatures come with a moderate uncertainty. If the clouds break across Central and Northern WA, temperatures will be capable of radiating well below freezing and does pose a small risk for patchy black ice Thursday morning, especially for roadways within the higher terrain (~ 3000 ft). If the clouds hold, temperatures will only flirt with 32F with a lower risk for ice development. A saturated boundary layer also suggest the potential for patchy fog and low stratus heading into Thursday morning.

Friday-Sunday: There is good agreement amongst the ensembles for the upper-low to remain anchored off the WA Coast through early Saturday then fill and weaken while ejecting inland Saturday night into Sunday. The position of this low off the coast does not pose a large risk for widespread precipitation Friday into early Saturday with highest chances for showers (30-40%) along the Cascade Crest and 5-15% elsewhere. Snow levels will waver from 2500-3500 feet in the Cascades so motorists should be prepared for light snow showers at times if traveling across the passes.

The threat for precipitation will increase Saturday into Saturday night and depart to the east on Sunday as the system tracks inland ushering a slow moving cold front from west to east. The main threat will be across the eastern two-thirds of the forecast area. Rain chances vary from 40-60% across North Idaho and southeastern Washington Saturday evening/night and 15-25% further west for locations like Ritzville, Republic, Colville, and Davenport. Spokane sits around 25-30% with highest chances after 11PM. Rainfall amounts look light and under a tenth of an inch through 11PM for most areas. After 11PM, rain will increase and become more steady across far southeastern WA and the lower Idaho Panhandle where there is a 20-40% chance for rainfall amounts to exceed a quarter of an inch. Dry and cool conditions are expected across Central WA Saturday evening into Saturday night. Winds Saturday evening will be light and generally under 10 mph with evening temperatures in the mid to lower 40s.

Monday-Wednesday: There is moderate confidence for any upper-level ridge to build over the Northwest during this period. This will promote near to warmer than normal temperatures, light winds, and largely dry conditions. The caveat comes Tuesday with ~50% of the ensembles indicating a few different potential outcomes where a weak wave slips through the ridge delivering a chance for light showers. By Wednesday, the ensembles re-align with nearly all outcomes showing the ridge back in place. All things considered, ridges in November can often lead to cool temperatures due to the lack of mixing, especially following precipitation. This will likely be the case for areas that pick up over an quarter of an inch of rain over the next few days. Fog and stratus can also be slow to burn off each morning. At this time, confidence is above normal for minimal weather impacts during this period. /sb

Aviation

00Z TAFS: Band of showers stretching from the OR/WA border to the Canadian border is bringing periods of MVFR ceilings and occasional lightning to GEG/SFF/COE/PUW. The showers are expected to go through 03Z. VFR conditions expected for EAT/MWH/LWS/PUW. MVFR ceilings expected to develop for GEG/SFF around 12-14Z. COE expected to have low cloud deck wavering between VFR/MVFR through the period.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in VFR conditions for EAT/MWH. Moderate confidence in MVFR ceilings for GEG/SFF/COE/PUW. HREF has a 40-50 percent chance. Sites could remain VFR. /JDC

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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 34 50 36 50 33 50 / 60 0 0 10 0 20 Coeur d'Alene 35 49 34 50 33 51 / 80 10 0 0 10 20 Pullman 36 51 36 49 32 51 / 20 10 0 0 10 30 Lewiston 40 54 39 54 37 53 / 30 10 0 0 10 20 Colville 34 48 34 49 27 50 / 50 20 0 10 0 10 Sandpoint 35 47 34 48 30 50 / 100 30 0 0 0 10 Kellogg 34 47 33 50 33 51 / 70 10 0 0 10 30 Moses Lake 33 53 36 51 28 51 / 0 0 0 10 0 10 Wenatchee 35 47 37 48 34 48 / 0 0 30 50 0 10 Omak 34 48 36 47 31 48 / 10 10 10 50 10 0

Watches, warnings and advisories

WA: Winter Weather Advisory until 5 PM PDT this afternoon for Western Chelan County. ID: None.