Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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286 FXUS66 KOTX 202120 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 220 PM PDT Mon May 20 2024 .SYNOPSIS... Showers will quickly diminish this evening with 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. The week and into the Memorial Day weekend will be cool, unsettled with thunderstorms each day, especially over the higher terrain. && .DISCUSSION... 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 && .AVIATION... 18Z TAFS: The Inland Northwest is on the back edge of an exiting upper level trough of lower pressure. There will be enough instability for convective showers and isolated thunderstorms to form this afternoon. Best chances of thunderstorms are expected in the Idaho Panhandle today with hazards that may include brief heavy downpours, small hail, and gusty outflow winds. An isolated cell or two cannot be ruled out over northeast Washington as well. 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: Some high resolution models show a potential for thunderstorms across northeast Washington today similar to what happened Sunday afternoon, so there is a 10-15% chance KGEG, KSFF, and KCOE would have thundershowers in the vicinity between 21-02Z today. /SVH ----------------------- 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 63 45 55 41 62 / 20 30 80 90 30 30 Coeur d`Alene 41 62 45 54 41 60 / 30 10 90 90 40 30 Pullman 38 61 44 52 39 57 / 10 10 90 90 50 30 Lewiston 45 70 50 60 46 65 / 0 10 90 90 50 30 Colville 41 63 40 55 36 64 / 20 40 80 90 40 50 Sandpoint 36 61 45 52 41 60 / 40 20 90 100 60 50 Kellogg 41 60 46 50 43 57 / 40 10 90 100 70 50 Moses Lake 45 67 45 62 44 72 / 10 40 50 60 20 0 Wenatchee 48 64 47 60 46 70 / 0 40 30 40 10 0 Omak 39 65 45 62 44 72 / 10 40 50 70 20 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$