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FXUS66 KOTX 252226 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 326 PM PDT Thu Apr 25 2024

SYNOPSIS
Rain will spread into eastern Washington and north Idaho this evening and linger into Friday morning. 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 vigorous frontal system.

DISCUSSION

Tonight into Friday: As of 2 PM, bands of rain were spreading into central Washington. The Wenatchee, Yakima, and Ellensburg airports had received a couple hundredths of an inch of rain, and light rain had spread into Ephrata and Moses Lake. By early evening, light rain bands will be approaching the Washington/Idaho state line. Despite the abundance of deep layer moisture with subtropical Pacific origins, rain amounts don't look impressive.
As the front moves across eastern Washington into north Idaho, it will splitting as the upper trough axis digs into southern Oregon and northern California. Frontal rain bands will also be fighting the central Washington downslope "rain shadow". Ensemble based guidance from the National Blend of Models only generates a few hundredths of an inch of rain this afternoon and evening across the Moses Lake area and the Columbia Basin. Spokane, Coeur d'Alene, and Pullman only have a 10 percent chance of a tenth of an inch by Friday morning. The only spots that have a greater than 50 percent of exceeding a quarter inch of rain tonight through Friday afternoon are mountainous areas north of Republic, Colville, Ione, and Sandpoint as well as the crest of the Cascades. Scattered post frontal showers will produce hit or miss rain Friday afternoon and evening. These showers will be the most concentrated over the mountains of north central and northeast Washington as mid-level southerly flow will contribute to orographic enhancement over the high terrain of Okanogan, Ferry, Stevens and Pend Oreille counties. There is a 10 to 20 percent chance of lightning Friday afternoon for these orographically favored areas as well.

Saturday: A weak upper trough will linger over the Inland Northwest on Saturday promoting another round of scattered mainly terrain enhanced showers. Again, a handful of lightning strikes are possible in our counties along the Canadian border with a 10 to 20 percent chance of spring thunderstorms for Ferry, Stevens, Pend Oreille, and Boundary counties. With the exception of these scattered showers, Saturday looks favorable for outdoor activities with afternoon highs ranging from the upper 50s in the Idaho Panhandle to the mid 60s in the Columbia Basin and Lewiston area. South winds will generally be in the 10 to 15 mph range with localized gusts to 25 mph over the Waterville Plateau and Okanogan Valley.

Sunday and Monday: Our breeziest weather over the next 5 to 7 days will occur Sunday and Monday as the Polar Jet becomes focused over the Pacific Northwest. The various ensemble clusters advertise a transition to a longwave trough over the Gulf of Alaska and British Columbia Sunday and Monday, but there are differences in the timing and strength of the shortwaves embedded within the increasingly swift westerly flow over Washington and Idaho. At this time, the most likely scenario supports increasingly breezy south or southwest winds on Sunday as the upper trough leans into the region followed by a distinctly cooler upper shortwave Sunday night into Monday with stronger west winds. Unfortunately, significant precipitation looks unlikely both Sunday and Monday across the Columbia Basin, West Plains, and most of the Palouse.
There is a less than 5 percent chance of a tenth of an inch of rain for Moses Lake and the Columbia Basin Sunday and Monday. And less than a 10 percent chance of a tenth for the Palouse and West Plains. With a good deal of spring farming activity during the last 2 weeks and very little recent moisture, we are concerned about blowing dust. The National Blend of Models generates a 30 to 40 percent probability of sustained winds of 20 mph or more across these agricultural areas Sunday afternoon and again Monday. We will continue to watch the wind forecast closely.

Tuesday through Thursday: The characteristics of the upper trough over BC become inconsistent by Tuesday and Wednesday. The majority of the ensembles sustain a trough along the coast...a pattern favorable for scattered showers over the mountainous terrain. However, about a quarter of the ensembles develop high pressure over the Inland Northwest. Needless to say, temperature distributions increase significantly in the National Blend of Models output by the middle of next week with high temperatures ranging from the 50s in the cool ensembles to the 70s in the warmer ones. /GKoch

AVIATION
00Z TAFS: A front passing through the region is beginning to spread rain into eastern WA and north ID. Light rain has already begun at MWH, EPH, and OMK, and is expected to reach the remaining airports within the next couple of hours. Ceilings are lowering, and potential for MVFR conditions will last into the evening and overnight hours.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate confidence in MVFR cigs around 01-06z light rain band.
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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 44 59 41 60 40 59 / 80 40 10 20 10 20 Coeur d'Alene 44 56 41 58 41 56 / 90 60 20 40 10 30 Pullman 43 57 40 57 40 57 / 80 40 20 20 10 20 Lewiston 48 64 45 64 46 65 / 80 50 10 10 10 10 Colville 41 58 38 60 36 58 / 90 80 40 60 30 30 Sandpoint 44 55 41 57 41 53 / 90 70 40 70 40 70 Kellogg 44 54 44 55 43 52 / 90 80 40 70 30 60 Moses Lake 42 66 41 66 41 65 / 40 20 10 0 0 0 Wenatchee 46 62 45 62 42 62 / 40 30 10 0 0 0 Omak 46 64 44 65 39 64 / 80 60 20 20 10 10

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

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