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FXUS66 KOTX 172341 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 441 PM PDT Fri May 17 2024

SYNOPSIS
Gusty winds will decrease this evening and subside overnight. Cooler and unsettled weather will continue through the weekend. Tonight will be quite chilly with the potential for frost in our sheltered valleys of north Idaho and northeast and north central Washington. A wetter low pressure system is expected on Wednesday and will keep temperatures below normal.

DISCUSSION
Tonight through Sunday Night: The upper level trough moved through earlier today and is already into western Montana. A boundary has set up across the Palouse and into the southern ID Panhandle where some showers are occurring. Earlier today around noon there were a few lightning strikes, but nothing since. The extensive cloud cover across NE WA and the north ID Panhandle has inhibited convective showers, but clouds appear on satellite to be thinning, and that area could see more pop up showers and an isolated strike through sunset. The showers are moving toward the southeast.

Winds continue across the Cascade gaps, Wenatchee/Waterville Plateau, Columbia Basin and onto the West Plains, Palouse, Lewiston/Clarkston area and the Camas Prairie. Winds are not as strong as they were yesterday. Winds ramped up again around 8 am and continued through the morning, but have been slowly decreasing this afternoon. Have cancelled the advisories as criteria is no longer being met.

Clouds will decrease tonight and with dry air in place in wake of the trough, we could see come pretty chilly temperatures Saturday and Sunday morning. Have higher confidence of near or below freezing temperatures Saturday morning than Sunday morning, as Sunday there will be some thicker clouds across the region as the next trough moves through the region. The 'typical' sheltered northern valleys of Washington and Idaho will see frosty conditions. Locations include but are not limited to: Colville, Newport, Usk, Deer Park, Priest Lake, Green Bluff area, Republic, parts of the Methow Valley. Actions should be taken to protect sensitive plants and vegetation if you live in sheltered valley that can typically get cold.

Saturday we are between systems, but 500 mb temperatures remain cold enough for a 20-30% chance of thunderstorms. The same is true for Sunday as a trough moves into the region. So the weekend is looking to be cooler with temperatures in the upper 50s and 60s and a 30-50% chance of showers for portions of the Inland northwest. Probabilities are less than 10% for central WA into the Moses Lake area, and are 60% or higher for the northern WA and ID counties. Winds will be less than what has been seen the last day, but Cascade gap winds will pick up each afternoon and evening with gusts 20-30 mph. /Nisbet

Monday through Friday: A longwave trough of lower pressure will settle over the west next week. Ensembles are in good agreement with shortwave trough digging over the region around Wednesday. There is some uncertainty with how deep this shortwave will get, but 50-60% of the ensemble members indicate a closed low forming over the Northwest region. Another 25% of the ensemble members keeps the wave open and more progressive, while 20% of the members has a weaker reflection of a shortwave pushing across. There is high confidence that temperatures will remain cool and below normal with high temperatures cooling into the 60s Wednesday into Thursday. A closed low will also result in a conditionally unstable air mass with unsettled conditions. Showers will be most prevalent during the afternoon hours as surface heating destabilizes the lower levels of the atmosphere. A cold pool overhead will also steepen mid level lapse rates with the potential for afternoon thunderstorms. Ensemble members diverge heading into the Memorial Day weekend period. Some members are slower in moving the upper level low out of the region off to the east. The general consensus is for the long wave trough to remain with temperatures warming slight but remaining below normal. /SVH

AVIATION
00Z TAFS: Gusty surface winds of 20-30kt will continue through 03z across the Columbia Basin, West Plains, and Palouse region before tapering off overnight. Scattered showers span across northeast WA into north ID with light precipitation, local MVFR conditions, and a 15% chance for a thunderstorm through 6z. Otherwise anticipate VFR conditions late tonight into Saturday. Confidence is low in a thunderstorm going over or approaching a TAF location, and short term TAF amendments will handle any thunderstorms.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High chance for VFR conditions late tonight into Saturday. ln

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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 39 62 39 61 40 68 / 10 30 30 40 10 10 Coeur d'Alene 38 59 39 57 40 65 / 30 40 50 60 10 10 Pullman 37 60 37 56 39 63 / 10 0 30 30 10 10 Lewiston 44 70 44 65 46 71 / 20 0 30 30 10 20 Colville 31 62 34 62 35 70 / 20 80 70 80 20 20 Sandpoint 37 57 39 55 37 64 / 50 50 60 80 20 30 Kellogg 39 57 40 52 41 61 / 50 40 40 70 20 40 Moses Lake 40 68 40 69 43 75 / 0 10 10 10 0 0 Wenatchee 45 64 43 66 45 73 / 0 10 0 10 0 0 Omak 39 66 40 70 42 77 / 10 40 30 20 10 0

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

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