Area Forecast Discussion

KEY MESSAGES

- Light snow in the east slopes of the Cascades into Friday morning above 3000 feet. Less than half of an inch of new snow expected.

- A chance (20-50%) of rain primarily over Southeast WA and the southern ID Panhandle late Saturday night into Sunday. Light rain accumulations up to a tenth of an inch expected.

SYNOPSIS

Low pressure will remain off the coast through Friday, then will eject inland over the weekend. Valley rain and mountain snow is forecast at times on Friday and through the weekend with periods of very light snow impacting the Cascade passes. The incoming low pressure system will also bring increasing chances for light rain late Saturday night into Sunday across Southeast WA and the southern ID Panhandle.

DISCUSSION

Friday through Sunday: The upper level trough off coast continues to weaken and fill in, but will leave cool and unsettled conditions present in the region through this weekend with temperatures near average to slightly below average. Shower chances Friday will be limited to the east slopes of the Cascades. Snow levels will be around 3000-4500 feet, so there is a small chance (10%) for 1" or more at Washington Pass.

The forecast for Saturday evening looks drier than it was looking last night but there are still a small chance for sprinkles (5-20% chance), mostly in central/eastern Washington and the southern ID Panhandle. Evening temperatures will fall into the low to mid 40s, accompanied by light northeast winds around 1-4 mph. The chance of seeing 0.25 inches or more of rain from 4 AM Saturday to 4 AM Monday has drastically dropped to less than 5 percent outside of the lower Palouse and L-C valley. The chances are around 10-20% with the highest on the Camas Prairie.

Shower chances Sunday will be limited to southeast Washington east of US-395 and the southern ID Panhandle as the trough moves ashore. The best dynamics appear to be trending southward in the model runs so the chances of a quarter inch or more of rain through Monday morning have dropped off significantly to less than 5 percent outside of the lower Palouse and L-C valley. The chances are around 10-20% with the highest on the Camas Prairie.

Monday through Thursday: Models are still in good agreement of a building ridge Monday which will bring dry conditions and slightly above normal temperatures in the low to mid 50s. High temperatures could under perform if stratus/fog layers develop but confidence is low at these lead times. Ensembles are trending towards unsettled conditions returning towards late next week (into Thursday) with potential for showers and high mountain snow. /DB

AVIATION

18Z TAFS: An influx of mid and high clouds over most of Eastern WA and North Idaho will lead to VFR conditions through 18z Saturday. Ceilings could be as low as 7-8k ft AGL between 03-18z Saturday which could present a small risk for sprinkles. For Central WA, upslope, easterly flow will lead to lower ceilings closer to 4000-5000 ft AGL in the Cascades with periods of light precipitation. This will lead to mtn obscrns over the higher peaks. There is low confidence for -RA at KEAT but 40% chance at Plain, Stehekin, and Winthrop with snow levels rising toward 4500 feet by this afternoon. Winds will be light for most terminals. The only exception will be 18-21z for KCOE and KPUW which will experience 10-14kts.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions prevailing except for at KEAT. There is moderate confidence for MVFR ceilings across the Cascades but low confidence to develop at KEAT.

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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 50 33 51 36 50 30 / 0 0 0 20 10 0 Coeur d'Alene 50 33 53 36 50 32 / 0 0 0 10 10 0 Pullman 50 32 50 33 44 29 / 0 0 0 10 30 0 Lewiston 54 37 54 41 49 36 / 0 0 0 30 50 0 Colville 49 27 52 25 53 22 / 0 0 0 20 0 0 Sandpoint 49 30 52 31 50 29 / 0 0 0 0 10 0 Kellogg 51 33 54 36 50 32 / 10 10 0 10 10 10 Moses Lake 53 28 53 32 54 27 / 0 0 0 20 0 0 Wenatchee 50 34 49 37 55 34 / 10 0 30 10 10 0 Omak 48 31 49 34 52 31 / 0 0 10 10 0 0

OTX WATCHES / WARNINGS / ADVISORIES

WA...None. ID...None.