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FXUS66 KOTX 210305 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 805 PM PDT Mon May 20 2024

SYNOPSIS
There will be a short break between weather systems into early Tuesday. Then a wet low pressure system is expected to move in the latter half of Tuesday into Wednesday, and linger into Thursday.
Another weather system will move in on Friday bringing more unsettled weather into the Memorial Day weekend.

DISCUSSION
Evening update: Shower activity is winding down with the loss of daytime heating. As of 745 PM a few showers lingered mainly over the Idaho Panhandle and made a few minor tweaks to the forecast based on radar trends. Also adjusted low temperatures for tonight, based on some of the newer guidance. Most of the changes were tweaks of a couple degrees, except for Colville where a more significant drop was made since last night got quite chilly (in the upper 20s) and there will be another opportunity for a quick drop in temperatures this evening as skies clear. JW

AVIATION
00Z TAFS: The Inland Northwest is on the back edge of an exiting upper level trough of lower pressure. Scattered showers will persist over the region through 03z with the highest focus over Northeast Washington into the Idaho Panhandle. There is a 15-20% chance of thunderstorms as well mainly east of a line from Colville to Spokane to Rosalia. These may include brief heavy downpours, small hail, and gusty outflow winds. Skies will clear out with loss of surface heating through the evening. A wet low pressure system will make its entrance on Tuesday with increasing clouds expected overnight.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is a 15-20% chance of thunderstorms at KGEG, KSFF, and KCOE through 03z this evening. Patchy fog is forecast 9-15z Tuesday in the mountain valleys of Northeast Washington and the Idaho Panhandle. This includes KCOE, but confidence is low given the expected patchy coverage.

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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

PREV DISCUSSION
/issued 449 PM PDT Mon May 20 2024/

Tonight: Convective showers this afternoon are much more subdued compared to this time yesterday. The low pressure trough axis has swung through into western Montana leaving the Inland Northwest on the back edge with cumulus build ups from differential heating combating subsidence aloft with higher heights moving in. There is still a 20% chance for a lightning strike or two with stronger updrafts, thunderstorm potential overall will be less compared to what we saw yesterday evening. Skies will then quickly clear out overnight. There will be the potential for a redevelopment of fog in the mountain valleys of northeast Washington and in the Idaho Panhandle tonight as the surface radiates out. Fog coverage is expected to be less and more so confined in the mountain valleys instead of extending out into the Spokane Area like it did earlier this morning.

Tuesday into Tuesday night: Tomorrow will start out dry, but a warm front will quickly move into the region ahead of a robust low pressure system that drops south across BC. The warm front will a shot of increased precipitable waters from around 0.45 inches to around 0.75 inches. The combination of good dynamics with the front drawing in ample moisture off of the Pacific Ocean will bring an increasing chance for rain through the afternoon and into the overnight hours. Light rain is expected to begin in the Cascades by noon, and then push east of the Cascades into the basin and Okanogan Highlands/Valley by mid afternoon. The thickening clouds and rainfall will subdue our warming through the day with high temperatures generally in the 60s.

Precipitation will become enhanced in the evening as it continues its march into the Idaho Panhandle by the late evening hours.
Steady precipitation into Tuesday night will result in soaking rains in the lowlands across much of the region. The exception will be in the lee of the Cascades where downsloping will result in less accumulations with places like Wenatchee, Quincy, and Ephrata struggling to receive at least a tenth of an inch of precipitation. Snow levels will be lowering late in the night into Wednesday morning as the cold front quickly catches up the warm front. /SVH

Wednesday through Sunday: Widespread rain is expected throughout the day Wednesday as the low continues to trek eastward. The forecast continues to be on track with the rain totals. Over the mountains, totals will be upwards of 0.5 inches to over an inch, with a quarter to half an inch in the lower elevations. The Columbia Basin will miss out on much of the rain with less than 0.05 inches expected. Snow will be limited to the highest terrain, with one to two inches forecasted at Washington Pass, and Stevens Pass will remain mainly as rain, with the possibility of a few snowflakes mixed in. This rain, along with additional snowmelt from the mountains will lead to a slight rise in creeks and rivers, but should remain below action stage. During the day on Wednesday, an isolated lightning strike is possible but don't expect to see any. Wednesday's temperatures will be the coolest of the week, with high temperatures in the 50s as the system passes through. In areas that receive limited rain could see breezy winds with gusts up to 25 mph mainly in the Columbia Basin and Waterville Plateau.

For Thursday through the weekend, scattered showers will continue, especially in northeast WA and ID Panhandle. Another low arrives late Friday into Saturday, with additional rain to the area.
Temperatures will conintue to stay slightly below normal for this time of year. Ensembles are hinting that by Monday, a ridge will begin to build, warming temperatures. /KM

PRELIMINARY POINT TEMPS/POPS
Spokane 41 63 45 55 41 62 / 0 30 80 90 30 30 Coeur d'Alene 39 62 45 54 41 60 / 10 10 90 90 40 30 Pullman 40 61 44 52 39 57 / 10 10 90 90 50 30 Lewiston 46 70 50 60 46 65 / 20 10 90 90 50 30 Colville 32 63 40 55 36 64 / 0 40 80 90 40 50 Sandpoint 36 61 45 52 41 60 / 10 20 90 100 60 50 Kellogg 40 60 46 50 43 57 / 20 10 90 100 70 50 Moses Lake 46 67 45 62 44 72 / 0 40 50 60 20 0 Wenatchee 49 64 47 60 46 70 / 0 40 30 40 10 0 Omak 42 65 45 62 44 72 / 0 40 50 70 20 10

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

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