Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
355 FXUS65 KBOI 180326 AFDBOI Area Forecast Discussion National Weather Service Boise ID 826 PM MST Mon Nov 17 2025 .DISCUSSION...Quiet wx in our CWA as an upper trough splits as it moves inland from the coast tonight. The south portion of the trough has become a closed low near San Francisco, headed toward southern California Tuesday like the previous upper low, while the north portion is forecast to move rapidly eastward along the Canadian border, leaving our CWA under weak flow aloft. The only pcpn should be light rain (light snow above 7000 feet Tuesday and 6000 feet Wednesday) in the West Central ID mountains as the north part of the trough moves past. More impactful wx might be valley fog Tuesday morning, patchy but possibly dense. Would be more concerned with a ridge overhead and an inversion below, or if the ground were snow-covered, but neither is expected. In any case, patchy fog will be there Tuesday, and to a lesser extent Wednesday, during morning commute time. Current forecast looks good vs latest models through Wednesday night so no updates should be needed. && .AVIATION...Pockets of MVFR/IFR from low clouds will persist across southeast OR and the southwest ID mountains overnight through Tuesday morning. Widespread mountain obscurations. Patches of LIFR fog will develop tonight into Tuesday morning, possibly continuing through afternoon. Surface winds: variable under 10 kt. Winds aloft at 10kft MSL: S-SW 5-15kt. KBOI...Mainly VFR through the evening and overnight with ceilings above 5000 ft AGL. A 20-30% chance of LIFR low clouds/fog developing Tuesday AM, highest west of KBOI. Surface winds SE or variable 5 kt or less. && .PREV DISCUSSION... SHORT TERM...Tonight through Wednesday night...A weak ridge will build back into the region this evening, bringing drying conditions and helping the showers across the area to taper off. Two cutoff lows will skirt our region today and tomorrow, with one diving down to the south and another moving north. This situates us in the deformation zone between the lows, with mostly dry conditions. Warm and moist southwest flow will continue to bring intermittent cloud cover tomorrow over the region, with clearing overnight allowing for fog formation in area valleys on Tuesday and Wednesday morning. There`s medium confidence in dense fog formation resulting in visibilities below 1/4 mile in lower elevation valleys tomorrow. A weak cold front will move into the region on Wednesday, bringing a 20-40% chance of mountain snow above 5000-6000 feet with valley rain in Baker County and the West Central Mountains. Temperatures will continue to cool throughout the short term period, but still be about 5-10 degrees above normal, with daytime highs in the Boise area in the mid to upper 50s through Wednesday. LONG TERM...Thursday through Monday...A very similar pattern to recent days will continue in the extended. An upper level trough will split at it approaches the coast on Thursday. The southern portion will develop into a cutoff low and move south into California, resulting in only a 20-40% chance of showers across our area. High pressure will then build overhead through the weekend. A temperature inversion may develop under stable conditions, and low clouds/fog may become persistent in the lower elevations if enough moisture gets trapped under the inversion. Temperatures are expected to average slightly above normal across the area, but if low clouds and fog do develop, that would reduce high temperatures. Moisture is expected to move over top of the ridge late in the weekend into early next week. Ensembles favor the ridge to be strong enough to keep the moisture to our north through Sunday, resulting in lower precipitation chances than previous forecasts over the weekend. On Monday, an upper level trough approaching the coast will bring a 30-60% chance of precipitation, with the highest chances in the northern mountains. Snow levels around 4500-6000 feet will keep precipitation as rain in the lower elevations, with snow accumulations limited to the mountains. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise DISCUSSION...LC AVIATION.....JY SHORT TERM...SA LONG TERM....ST