120 FXUS65 KBOI 151522 AFDBOIArea Forecast Discussion National Weather Service Boise ID 922 AM MDT Mon Sep 15 2025
.DISCUSSION...Mostly sunny today (except in Valley County, ID), and breezy from the northwest as upper low in western MT moves east, then warming and drying through Friday as the next upper ridge comes in from the west. Friday looks like the warmest day, then slight cooling along with a 15-25 percent chance of showers Saturday and Sunday, and large forecast uncertainty after that. Near-surface HRRR smoke will be minimal through Tuesday. Current forecast is in good shape. No updates.
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.AVIATION...VFR. Isolated rain showers and local mountain obscuration in the west central Idaho mountains through this afternoon. Patchy valley fog and low stratus in northern mountains around sunrise Tuesday. Surface winds: Generally W-N 10-20 kt. Winds aloft at 10kft MSL: NW 10-15 kt.
KBOI...VFR. Few afternoon cumulus, otherwise clear. Surface winds: NW around 10 kt.
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.PREV DISCUSSION... SHORT TERM...Today through Wednesday night...A few showers are expected to linger this morning across the west-central Idaho mountains as the upper-level trough continues its slow eastward progression over the northern Rockies. This will maintain a threat for showers and thunderstorms (20% chance) through the afternoon. The primary impact will be cooler, northwesterly flow across the area, which will keep temperatures about 7 degrees below normal. We are also expecting breezy westerly surface winds across the Snake River Plain. An upper-level ridge will build into the region on Tuesday, allowing temperatures to moderate back to near normal. The ridge will remain in place through Wednesday, with temperatures warming to near 5 degrees above normal.
LONG TERM...Thursday through Monday...An upper-level ridge will continue to build across the region on Thursday, bringing clear skies and slightly above-normal temperatures, with highs expected to be about 5 degrees above normal. On Friday, the ridge axis will gradually shift eastward, allowing for the return of a south-to-southwesterly flow aloft. This pattern change is driven by an upper-level trough off the coast of California. As the ridge continues to weaken, the chance of precipitation will slowly increase on Friday afternoon and then rise further through Saturday and Sunday. There remains large variation in long-range model solutions for how this pattern evolves. Therefore, confidence is low in any specific details beyond this period.
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.BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None.
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DISCUSSION...LC AVIATION.....LC SHORT TERM...JDS LONG TERM....JDS
NWS BOI Office Area Forecast Discussion