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FXUS66 KOTX 101144 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 444 AM PDT Fri May 10 2024

SYNOPSIS
Temperatures today through the weekend warm to the highest values of the season so far, with highs reaching the 80s and a few areas the lower 90s. The weather pattern for early next week is uncertain, however a cooling trend is likely with increasing clouds, and a small chance of precipitation for the Cascade Crest, northeast Washington, and the northern half of the Idaho Panhandle.



DISCUSSION
Friday through Sunday: Dry and quiet weather will continue through Saturday as a large ridge sits over the Pacific Northwest and a closed upper level low sits over Great Basin. This rex block pattern will keep the ridge nearly stationary over the northwest today and tomorrow. This will allow temperatures to warm into the upper 70s to low 90s today and tomorrow, which are about 10 to 20 degrees above average for this time of the year. Those who are sensitive to heat or not yet acclimated to this type of heat should plan to take some extra precautions if planning to spend time outside this weekend.
Water temperatures for lakes and rivers across the region are on average in the upper 40s and low 50s. Please be mindful of this if planning to spend some time near or on the water. Hypothermia and loss of muscle control happens very quickly when swimming in water temperatures this low.

The ridge will begin to weaken and shift eastward late Saturday into Sunday as a shortwave approaches the northwest. The cross-Cascade pressure gradient will begin to tighten Saturday afternoon and evening as the flow shifts onshore, resulting in breezy winds through the Cascade valleys. As the shortwave nears Sunday, the Cascade valleys will experience some marginal cooling, but temperatures will still be very warm regionwide. Winds will pick up region wide on Sunday. Current forecast has the strongest gusts across the lee of the Cascades from the Okanogan Valley, the Waterville Plateau, and the western Columbia Basin. Following the stretch of very warm and dry weather, these winds will bring an increased risk for quick moving dead grass and brush fires. /vmt

Sunday night to Thursday: The ridge flattens near the start of the week, with a shortwave trough migrating through before there is an opportunity for the ridge to rebound toward the middle part of next week. However by mid to late week guidance continues to diverge, showing either an amplifying ridge or another wave coming in. First between Sunday night and Tuesday look for variable cloud cover, with breezy conditions. Limited shower chances will be found near the Cascade crest and Canadian border Sunday night, expanding over more of the northern WA and ID Panhandle mountains for Monday and Tuesday. The best chances, overall, appear to be Monday. Some guidance even expands some potential over Spokane/C’dA and Palouse. I give a nod to ensembles painting a 10-40% chance of measurable precipitation by adding some slight chances around the Spokane/C’dA area; I held off on the Palouse as the ensembles probabilities are more borderline there. There will also be limited t-storm chances especially on Monday afternoon and evening, with the shortwave encountering a projected 200-400 J/kg of SBCAPE. However Sunday evening may also see a few embedded t-storms. These chances will largely be toward the NE WA and N ID Mountains.

As for winds, the incoming shortwave will bring some of the stronger winds near the Cascades expanding out into the western Columbia Basin Sunday night. Sustained winds between 15-25 mph will be possible with gusts up to about 40 mph. Elsewhere winds will increase some with gusts near 15-20 mph. Broader breezy conditions will be found Monday and Tuesday, though the extremes are more washed out by then as the primary front will have shifted through leaving sustained winds 10-15 mph and gusts of 20-25 mph.

Heading into Wednesday and Thursday the model disagreement starts to impact the forecast. If a stronger ridge returns it will be drier and if a trough dominates it will be wetter. A middle ground approach shows some slight to chance PoPs around the mountain zones and eastern third of WA and lower ID. It will also remain potentially breezy, but marginally.

Temperatures drop down Monday into Tuesday with the trough in the region, meaning highs in the upper 60s and 70s, with a few areas near 80 in the deeper Columbia Basin. Wednesday into Thursday forecast temperatures are held near persistence from Monday and Tuesday. However if the ridge manifests stronger it could be warmer and if a deeper trough comes in it could be cooler. Models show about a 20 degree range in potential highs by Thursday. For example, most recent guidance in Spokane shows it could be as cool as 65 or as warm as 81. /Solveig

AVIATION
12Z TAFS: Widespread VFR conditions are expected through the TAF period as high pressure builds over the region. Winds will be light through the period except for breezy winds through the Cascades valleys, including KEAT, in the evenings.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is very high confidence for VFR conditions across all TAF sites.

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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 80 49 82 53 83 53 / 0 0 0 0 0 0 Coeur d'Alene 79 49 80 52 80 51 / 0 0 0 0 0 0 Pullman 76 48 79 51 78 51 / 0 0 0 0 0 0 Lewiston 81 54 85 56 86 56 / 0 0 0 0 0 0 Colville 82 47 83 48 83 48 / 0 0 0 0 0 10 Sandpoint 77 49 79 51 78 50 / 0 0 0 0 0 10 Kellogg 76 52 77 54 77 53 / 0 0 0 0 0 10 Moses Lake 86 52 89 52 89 53 / 0 0 0 0 0 0 Wenatchee 84 58 88 58 86 55 / 0 0 0 0 0 0 Omak 86 53 89 53 88 52 / 0 0 0 0 0 0

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

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