Marine Weather and Tide Forecast for Ponderay, ID

DISCUSSION
Today through Sunday: Overall, the forecast is remaining on somewhat on track from this morning. There is some lingering uncertainty whether Spokane/Cda near 2000 feet can change back to snow as colder air aloft arrives but radar suggests a more organized band is not going to take shape. Spokane to Deer Park has a 10-20% chance of an inch of snow by 8 PM, 40% chance Colville, 60% chance for Newport, 80% chance Metaline falls. The cold front appears to have crossed through Everett and is quickly progressing eastward on radar and satellite. A convergence zone will form shortly as the front crosses the Cascades this afternoon, opening the window for 1-2" an hour snowfall rates at Stevens Pass this evening. There is a 20-40% chance for 3+" an hour around 6-10 pm. Storm total snowfall will be greatest near Stevens Pass above 3500'. There is a 60% chance of 24" or more through tomorrow afternoon at the pass level. Lookout pass has a small window around 4-7 pm for 1"/hr snowfall rates associated with the current band of precipitation on radar.

Behind the front passage tonight, the INW will be left in a cold and conditionally unstable environment with moderately steep mid-level lapse rates. Mountain snow showers will continue in the Cascades but a weak wave over SW BC will spark some lowland snow showers tomorrow morning in the eastern third of WA/ID Panhandle.
With this round of snow showers, lowland towns have some additional chances for an inch or more of snow during the day Sunday: Sandpoint/Cda: 20%, Pullman: 40%, Winchester: 80%. /DB

Monday through Saturday: Models are in good agreement through the week. An upper ridge will build over the region on Monday and Tuesday for mainly dry weather. An abundance of boundary layer moisture and light winds will support an expansion of freezing fog and stratus as low temperatures drop into the mid 20s to low 30s.
Then a series of mid level waves track through the region with each one getting slightly stronger. The first one arrives Tuesday Night into Wednesday. The NBM is only giving a 5-10% chance of precipitation but with all the stratus it wouldn't take much for some light precipitation so this will be monitored. The next wave arrives on Thursday with the majority of the ensembles producing light snow over the region. The exception is the Lewiston- Clarkston Valley where a rain/snow mix is favored. Then another system arrives on Saturday. While this looks to be the period with the highest precipitation chances of the extended, ensembles show a wide range regarding precipitation amounts so confidence in the details is low. JW

AVIATION
18Z TAFS: Complex precipitation types across the region today as a cold front sweeps through. A warm layer aloft will gradually cool with some of the latest forecast soundings showing rain and freezing rain changing to snow over NE Washington and the Idaho Panhandle between 22z-24z so have indicated this in a TEMPO group for KGEG/KSFF/KCOE. Brief accumulation up to 1" is possible for KGEG/KCOE if the snow comes down heavy for a couple hours. The smaller airports north of KGEG/KCOE could see changeover to snow earlier (19z-22z). For KEAT/KMWH all the precipitation will occur before the warm layer cools support mainly freezing rain and rain. For Pullman and Lewiston temperatures are already above freezing with just a rain event. After the cold front passes, the forecast gets tricky as an abundance of boundary layer moisture remains but an increase in winds. Given all the moisture and looking at the HRRR IFR/MVFR conditions are likely for much of Eastern WA/N Idaho, except KEAT/KLWS which may benefit from downslope flow off area mountains.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is low to moderate confidence in the precipitation type forecast today across the region, except for high confidence at KPUW/KLWS. There is low confidence with the ceiling and visibility forecasts through Sunday morning with multiple cloud layers over the region.
JW

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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 31 37 25 32 27 33 / 60 40 0 0 0 0 Coeur d'Alene 31 36 26 33 29 34 / 90 60 10 0 0 0 Pullman 32 37 28 35 25 36 / 100 60 30 0 0 0 Lewiston 36 45 32 42 29 38 / 90 40 20 0 0 0 Colville 27 35 18 31 24 30 / 40 20 0 0 0 0 Sandpoint 30 35 25 34 27 32 / 100 60 10 10 0 0 Kellogg 32 35 28 35 28 34 / 100 90 30 30 0 0 Moses Lake 30 39 24 32 28 33 / 10 10 0 0 0 0 Wenatchee 33 41 28 35 28 32 / 20 20 0 0 0 0 Omak 29 37 24 33 26 30 / 20 10 0 0 0 0

OTX WATCHES/WARNINGS/ADVISORIES
ID...Winter Weather Advisory until 10 PM PST this evening for Northern Panhandle.

Winter Weather Advisory until 4 PM PST Sunday for Central Panhandle Mountains.

WA...Winter Weather Advisory until 10 PM PST this evening for Northeast Mountains.

Winter Weather Advisory until 7 PM PST this evening for Central Chelan County-Moses Lake Area-Okanogan Highlands-Okanogan Valley-Spokane Area-Upper Columbia Basin-Waterville Plateau- Wenatchee Area-Western Okanogan County.

Winter Storm Warning until 4 PM PST Sunday for Western Chelan County.