443 FXUS65 KBOI 120314 AFDBOIArea Forecast Discussion National Weather Service Boise ID 914 PM MDT Thu Sep 11 2025
.DISCUSSION...A few thunderstorms are still active late this evening, but radar trends show diminishing coverage and intensity. For the most part storms today brought heavy rain, and hail and not much wind. Shower and thunderstorm coverage will decrease overnight, with any lingering chance (15-20%) across the Wallowas and w-central Idaho mtns. At this time any flood/hail threat is over for tonight. Coverage will increase again Friday afternoon across higher terrain, though lower elevations in Oregon could get into the mix as a faster steering flow aloft will push storms off higher terrain (from north to south). Current forecast is on track for tonight with most areas going dry and potential mtn valley fog after midnight.
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.AVIATION...Showers and thunderstorms will taper off overnight. Patchy fog is expected in mountain valleys and highland basins tonight, especially KMYL, but also may develop near KBKE/KBNO. Scattered showers and thunderstorms developing on Friday over the higher terrain with localized MVFR/IFR conditions and mountain obscuration. Storms may produce heavy rain, small hail, and gusty outflow winds to 35 kt. Surface winds: light and variable overnight, becoming W-NW 5-15 kt on Friday. Winds aloft at 10kft MSL: Variable up to 10 kt.
KBOI...VFR with scattered-broken mid level clouds. Surface winds: SE around 5 kt overnight, becoming NW 5-10 kt Friday afternoon.
Weekend Outlook...Isolated showers and thunderstorms over the higher terrain on Saturday, but otherwise drier conditions with mostly clear skies will briefly return. Fog may develop in mountain valleys each night. Shower and thunderstorm chances will increase on Sunday as a trough and cold front approach. Surface winds SW-NW 5-15 kt.
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.PREV DISCUSSION... SHORT TERM...Tonight through Saturday night...Convection has already begun today, with scattered light showers and thunderstorms expected to become numerous later this afternoon trough this evening. Rain rates will increase, with stronger storms capable of heavy rainfall, small hail, and outflow gusts up to 45 mph. A slight deviation in the low has shifted our area of burn scar flash flooding concern from Oregon to Central Idaho. While burn scars in Oregon will still receive some rain, the bulk of the moisture seems to be passing north now. In Idaho, the change has moved moisture over very reactive burn scars, with convection already over areas including the Wapiti burn scar, so the Flash Flood Watch has been moved to Central Idaho.
Chances of precipitation across the area outside of areas previously mentioned vary greatly from 20% to 50%, generally decreasing the closer you get to the center of the low which is projected to move over the Treasure Valley and lower Snake Plain. Heavy rain will be mostly limited to Eastern Oregon and Central Idaho mountains. Precipitation begins to taper off after about 9PM MDT through Midnight. Overnight, light showers may continue across northern portions of our forecast area, before scattered showers and isolated storms form across Baker and Valley counties, as well as the NV border. As the low exits eastward Friday night, conditions warm and dry as a shortwave ridge moves in for the weekend, bringing temps back to near normal.
LONG TERM...Sunday through Thursday...An upper level trough will move through the Pacific Northwest on Sunday. The bottom portion of the trough will bring a pocket of moisture and a 20-50% chance of showers/storms to the area, with the greatest chance in mountains. As it exits to the east on Monday evening, showers and storms continue to be possible in central ID. The related cold front will also bring breezy winds and cooler temperatures on Monday. Tuesday through Thursday a ridge begins to amplify, warming temps and clearing skies. Models diverge after Thursday, but deterministic models show a deep trough moving close to the PacNW and Canadian West coasts. Ensemble means project it steadily moving inland, which would bring a day or two precipitation, a cold front and breezy winds. After the 5-10 degree below normal day on Monday, temps warm back up to a few degrees above normal through the week.
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.BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None.
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DISCUSSION...DG AVIATION.....ST SHORT TERM...JM LONG TERM....JM
NWS BOI Office Area Forecast Discussion