Sunrise 6:26 AM   Sunset 8:55 PM Moonrise 11:50 PM   Moonset 6:27 AM

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FXUS66 KOTX 261203 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 503 AM PDT Fri Apr 26 2024

SYNOPSIS
Friday will feature another round of showers, some capable of thunder in the northern mountains and ID Panhandle. The weekend and early next week will feature showery weather over the mountains and seasonably cool temperatures. Sunday and Monday have the potential to be windy with the passage of a frontal system.

DISCUSSION

Showers will persist through much of the day as a surface low off the WA coast slowly moves inland. Models indicate a slim chance (15%) of thunder with some surface based instability building in the northern mountains, Panhandle, and SE WA late this morning into the early afternoon. Looking at some short-range ensemble soundings, I am not sold on any strikes given the huge differences of instability between the surface based parcel and a mixed layer parcel. Pockets of heating from the sun will spark shower activity nonetheless.

The upper low quickly moves south of our area tonight but another shortwave moving in bringing additional chances of showers to the region for Saturday. Models indicate a slim chance (15%) of thunder with some surface based instability building in the northern mountains Saturday, but again, not sold on this potential given how little instability there is for a mixed layer parcel. /Butler

Sunday - Tuesday: The start of the new week will come with several days of windy conditions, cooling temperatures, and periods of showers...especially in the mountains. Midlevel flow on Sunday will start off westerly then begin to buckle to the southwest as a deeper low carves into the mean trough. A strengthening surface low east of Canadian Rockies will result in increasing southerly winds through the day. Winds have decreased slightly from earlier runs but still are noticeably breezy to gusty with sustained winds of 10-20 mph and gusts up to 30 mph. The cold core shortwave swings into the Northwest Sunday night and Monday with continued windy conditions. Winds continue to be driven by a strong pressure gradient toward lower pressure over southern Alberta and further enhanced with cold air advection. Wind direction will become more westerly with time as well, especially into Monday afternoon.
Based on probabilities for sustained wind speeds of 20 mph or greater - Sunday and Monday indicate very little difference (both around 40%) for much of the Central Columbia Basin. The main difference will be the directional change from south/southwest to southwest/west. Majority of the European members suggest the gusts will be several mph higher for Monday vs Sunday for locations like Wenatchee, Moses Lake, Pullman, and Spokane. For the Okanogan Valley, Sunday looks be the windiest day given the alignment with the north to south valley. In general wind gusts over the two days will peak around 30-35 mph yet some isolated gusts around 45 mph cannot be ruled out with the shortwave passage Sunday night and Monday on the higher benches around Wenatchee, Waterville Plateau, and in the foothills of the Blue Mountains. Westerly winds remain breezy on Tuesday but speeds are roughly 1/2 of those from Monday.

Current thinking is Sunday will provide a period of drying from the recent rainfall and Monday could be the day most vulnerable to patchy blowing dust in the Western Columbia Basin. We know agriculture practices are in full swing for planting but predicting blowing dust always comes with low confidence, especially without very warm and dry conditions during the winds.

In regards to precipitation, scattered showers will mainly focus over the Cascade Crest and into the rising terrain of Northeastern WA and North Idaho. Showers will expand at times into the eastern Basin and Palouse with the greatest threat coming with the shortwave passage Sunday night and Monday. A few lightning strikes will also be possible with weak thunderstorms in the afternoon.
Snow levels will be crashing closer to 3000-3500 feet Sunday night and Monday as 850mb temperatures drop near 0C. Consequently, snow is likely to fall along the Cascade Passes. Forecast has 4-6 inches of snow at Stevens Pass and 2-4 inches at Washington Pass from Sunday evening through Monday morning. Those venturing across the passes should be prepared for winter travel conditions during this time. Additional snow showers will continue Monday but the April sun angle offers little hope for snow to accumulate on roads after 9-10AM. It not be as snowy at Lookout Pass during this time-frame with only an inch predicted Sunday night into Monday morning though conditions could change so be sure to up to date if traveling early Monday morning.

Monday will be the coolest day of the period with most communities only reaching the 50s and a handful of low 60s in the lower Basin. Sunday and Tuesday will be more seasonal with upper 50s-60s. Those with sensitive plants may want to keep an eye on Tuesday morning lows near freezing within the mountain valleys and across the upper Basin.

Wednesday - Friday: There is a 70% chance that shortwave ridging arrives Wednesday. This scenario will promote light east/southeast winds and temperatures in the 60s. A few showers will linger in the Idaho Panhandle while the Cascades dries out.
The other 30% of the ensembles say no-no and the trough will persist with cooler temperatures and more widely scattered afternoon showers. Follwing Wednesday 60% of the ensemble members showing another trough into the Northwest while the other 40% are in some sort of transition from ridge to trough. Any blended forecast approach like the NBM is expected to struggle resolving these details and it's difficult to extract details in the forecast. If the trough was to remain off the coast, temperatures will be warmer than forecast and the opposite can be said if the trough comes inland. These differences will also impact the forecasted precipitation chances. Needless to say, there is a lot of uncertainty with the details for late next week so stay tuned.
/sb

AVIATION
12Z TAFS: MVFR conditions are projected through the morning, then conditions improve toward VFR with additional shower chances expanding. Toward central WA, including MWH and EAT and OMK, look for mainly VFR conditions.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate confidence in MVFR cigs over GEG/SFF/COE/PUW/KLWS Friday morning.
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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 60 42 61 40 59 40 / 30 20 20 10 10 20 Coeur d'Alene 58 42 59 41 56 39 / 50 20 40 20 20 30 Pullman 58 40 58 39 57 38 / 40 20 20 10 10 40 Lewiston 64 46 65 46 65 45 / 40 20 10 10 0 30 Colville 60 38 61 36 59 36 / 70 50 70 30 30 50 Sandpoint 55 42 57 41 53 40 / 70 40 70 40 60 60 Kellogg 56 43 56 43 53 40 / 70 50 70 30 60 60 Moses Lake 66 40 66 40 65 40 / 10 10 0 0 0 0 Wenatchee 63 44 62 42 61 40 / 40 30 0 0 0 10 Omak 63 43 66 39 63 39 / 50 40 20 10 0 10

OTX WATCHES/WARNINGS/ADVISORIES
ID...None.
WA...None.

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