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FXUS66 KOTX 200957 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 257 AM PDT Mon May 20 2024

SYNOPSIS
There will be a brief break between weather systems Monday into Tuesday. Then a wet low pressure system is expected late Tuesday and Wednesday, lingering Thursday. Another weather system will move in on Friday. The week and into the Memorial Day weekend will be cool, unsettled with thunderstorms each day, especially over the higher terrain.

DISCUSSION
Today: Skies have been clearing overnight with some lingering clouds from Pullman Washington into the Lewiston/Clarkston valley.
Clearing skies helped promote some patchy fog from North Spokane Mead and Dartford areas to around Deer Park. Temperatures around Deer Park are near freezing so local roadways may be slick during the morning commute. The fog is fairly shallow so it should dissipate fairly quickly after sunset. The frost advisory goes until 8 am this morning and looks good from that perspective.

* More Thunderstorm Potential Today: We'll be looking for additional cloud buildups today with a slight chance of thunderstorms similar to but not as far quite as far west as yesterday. Stevens and Pend Orielle county of Washington and the north Idaho have enough potential instability to support showers turning into a few lightning strikes this afternoon. Storm track will be northwest to southeast which is similar to yesterday. With high pressure building in from the west this should cap thunderstorm convection any further west but mountain showers in north central WA will still pop up as well. Wind gusts to 30 mph with pea sized hail and lightning are still the main threats going into the afternoon and early evening hours.

Tonight through Tuesday: After early evening convection winds down we'll have brief high pressure building over the Inland Northwest. High clouds coming in ahead of the next weather system will keep temperatures a bit warmer than the last few days for reduced frosting potential. Northern valleys still will dip down to around 36 degrees at Republic and Deer park though but these are typically cooler spots.

Clouds continue to increase Tuesday with light rain across the region into the Idaho Panhandle by around noon. TC

Tuesday Night and Wednesday: An upper level low pressure system will approach the region from the northwest Tuesday afternoon and by the evening precipitation will be spreading across the region.
Nearly every location will see precipitation from this weather system Tuesday Night and Wednesday. Ensemble guidance suggest probabilities of a quarter inch or more of rain for portions of central WA range from 10% around Wenatchee to 25% around Moses Lake to around 50% across the northern Waterville Plateau. There is a 50-65% probability across north central WA and into the Spokane area and down to the Palouse and LC Valley. As you head into northeast WA and the ID Panhandle, probabilities go up to 80% or higher. Portions of the ID Panhandle could see upwards of three quarters of an inch with this midweek system.

Snow levels will lower to 4000-4500 ft Wednesday morning. Snow may briefly mix in at Stevens Pass with little to no accumulation.
Washington Pass will see snow accumulation, with a 50% chance of an inch, and a 30% chance of 2 inches.

As the low moves into the area Wednesday there is enough instability for a 20% chance of thunderstorms in the afternoon across portions of eastern WA and the entire ID Panhandle.

Thursday through Memorial Day: The trough moves over the Divide and precipitation chances lower. However, afternoon showers and thunderstorms are possible across northeast WA and the ID Panhandle.

Friday another low pressure system moves into the region. Showers and thunderstorms remain in the forecast. Instability looks a bit better Friday compared to Wednesday. Saturday the low exits the region into Montana, and we remain cool and unsettled with showers and thunderstorms. Sunday 45% of the ensembles show a ridge of some kind over the Inland Northwest, with 55% keeping it more troughy. Finally by Monday there appears to be better agreement of the ridge setting up, just in time to finish your Memorial Day weekend drier with warmer temperatures. /Nisbet

AVIATION
06Z TAFS: Patchy fog or low stratus will be possible Monday morning in mountain valleys of northeast Washington and the Idaho Panhandle. Showers with isolated thunderstorms will mainly be confined to extreme eastern Washington and the Idaho Panhandle for Monday afternoon. Hazards include infrequent lightning, brief heavy downpours, pea sized hail, and gusty erratic winds up to 25-30 kts with stronger thunderstorms.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There's a 15% chance for low stratus producing MVFR conditions along the Spokane-Coeur d'Alene corridor Monday morning. This will be dependent on additional rain that this evening that moistens the boundary layer. Some high resolution models show greater storm coverage into central Washington Monday similar to what happened this afternoon.

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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 67 42 63 45 54 42 / 10 10 20 80 90 50 Coeur d'Alene 65 41 62 45 52 42 / 30 20 20 90 100 60 Pullman 62 39 61 44 51 40 / 10 10 10 80 90 60 Lewiston 70 45 70 50 59 46 / 10 0 10 80 90 60 Colville 69 37 63 40 54 38 / 10 10 30 80 100 50 Sandpoint 62 40 61 45 51 42 / 40 30 20 90 100 60 Kellogg 60 42 60 46 49 43 / 30 40 20 80 100 80 Moses Lake 74 43 67 45 59 44 / 0 0 20 20 60 20 Wenatchee 72 48 64 47 59 46 / 0 0 30 20 40 10 Omak 74 44 65 45 59 43 / 0 10 30 50 70 20

OTX WATCHES/WARNINGS/ADVISORIES
ID...None.
WA...Frost Advisory until 8 AM PDT this morning for Northeast Mountains-Okanogan Highlands-Upper Columbia Basin.

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