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FXUS66 KOTX 291133 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 433 AM PDT Mon Apr 29 2024

SYNOPSIS
Today will be windy with snow in the Cascade mountain passes through this morning and rain to much of the rest of the region.
Temperatures will trend cooler with areas of frost returning Tuesday morning. Unsettled conditions return for the remainder of the week, especially to the mountains.

DISCUSSION

Today through Tuesday Night...As the trough advances inland, we will see an increase in westerly winds today. While much of the area will see the increase in winds, the strongest will be over the Waterville Plateau with gusts up to 40 mph. Everywhere else, gusts of 25 to 35 mph are expected. Blowing dusts is also possible over the Columbia Basin as the winds increase in the afternoon.
Along with the winds, showers will increase late this morning over the Cascades, eastern third of WA and the ID Panhandle. These showers could contain steady rain and/or graupel with amounts above a tenth of an inch, with a quarter inch or more over the higher terrain. A few lightning strikes withing the strongest showers is possible as there is some instability in the atmosphere.

With the cooler temperatures over the Cascades, precipitation will fall as snow through the morning. A Winter Weather Advisory is in effect through 2AM Tuesday for elevations above 3500 feet in the Cascades. Snow will continue through the morning hours, with the likelihood of snow melting off the road in the afternoon due to the high sun angle. Models are indicating of snow banding occurring later this evening, with an additional few inches of snow, before decreasing overnight. Above, 3500 feet, expect snow totals of 4 to 7 inches with Stevens Pass receiving 8 to 10 inches of snow. Snow is also likely to fall over Lookout Pass but amounts of 1 to 3 inches are anticipated.

Another shortwave will slide through the region Tuesday with a return of showers and/or graupel by Tuesday afternoon, along with a slight chance of thunderstorms not out of the question during the afternoon and evening. Winds will also be a bit breezy, but will not be as high as what is seen today. As we move into Tuesday night, the threat of showers will decrease

High temperatures will hover around 50, with lows dipping into the low to mid 30s, leaving a heightened risk of frost across the area. Those with sensitive plants should take precautionary measures, particularly as temperatures flirt with freezing. /KM

Wednesday to Sunday: The Inland NW will remain in an active pattern, but model agreement continues to falter toward next weekend. Wednesday the area remains under the influence of an upper trough. The area will be cold enough in the morning to bring potential frost from the Upper Columbia Basin to the northeast WA and north ID valleys, including some of the Spokane area. Rain and snow shower chances will continue around the Cascades and Idaho Panhandle, with slight chances near the WA/ID border. These will be most numerous in the afternoon hours and decrease after dark. Thursday another sharp shortwave drops into the region.
Frost will remain possible in the morning over eastern WA and ID, though coverage looks less over eastern WA compared to Wednesday morning. The trough itself will bring higher and broader shower chances to the region, compared to Wednesday. There is a little CAPE (near 100 J/kg) so some isolated embedded t-storms cannot be ruled out, but overall they are not expected to be a big impact.
Going into Thursday night models start to diverge in terms of how quickly to move this shortwave out. Some wrap a deformation axis back into southeast WA and lower ID, providing a focal point for moisture and better precipitation potential. So the details will warrant more fine-tuning.

A weak ridge builds in Friday, with shower chances lingering over the region. Then heading into the weekend another shortwave trough digs into the West, but here models either show it tracking south and bringing very limited precipitation chances to the region or tracking it directly into the region with broader and higher precipitation chances. About 70% of the solution suggest a pattern still dominated by a trough, but 40-50% show a stronger trough. Overall this will continue to support precipitation chances through the weekend, but some of that weekend could be much wetter if some solutions verify. Confidence is low at this point.

Expect a warming trend into Saturday. Yet by Saturday and Sunday there is a broader range of possible temperatures, with as much a 15 degree spread in the 25-75 percentile by Sunday. This is the difference of highs in the upper 50s or highs near 70. Expect some breezy conditions Wednesday and Thursday and again possibly toward the weekend. Speeds are nothing that appears would necessitate any highlights but still noticeable with gusts near 15-20 mph. /Solveig

AVIATION
12Z TAFS: Showers will increase in coverage over the region especially over the Idaho Panhandle and eastern third of Washington. There is a 20% chance of thunderstorms for the eastern third of WA. The showers will moisten the boundary layer with areas of MVFR conditions developing this afternoon between Pullman and Spokane and into the Idaho Panhandle.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is about a moderate chance of blowing dust across the Columbia Basin this afternoon, including MWH. Given low confidence in precise timing and limited coverage of thunderstorms did not include for these 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 51 31 50 34 59 36 / 80 30 30 10 10 10 Coeur d'Alene 47 30 47 33 54 34 / 100 40 40 20 20 10 Pullman 46 31 46 32 53 34 / 90 40 60 20 30 10 Lewiston 54 36 53 37 59 38 / 90 30 60 30 20 10 Colville 50 26 51 30 60 33 / 80 40 30 10 10 10 Sandpoint 47 30 45 34 51 36 / 90 60 60 20 40 10 Kellogg 43 31 42 34 49 35 / 100 60 70 30 50 20 Moses Lake 57 33 56 34 66 38 / 40 0 10 0 0 10 Wenatchee 54 37 55 38 63 41 / 40 10 10 0 0 10 Omak 56 32 55 35 65 40 / 30 10 10 0 10 10

OTX WATCHES/WARNINGS/ADVISORIES
ID...None.
WA...Winter Weather Advisory until 2 AM PDT Tuesday for Western Chelan County.

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