Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
655 FXUS65 KBOI 201044 AFDBOI Area Forecast Discussion National Weather Service Boise ID 344 AM MST Thu Nov 20 2025 .SHORT TERM...Today through Saturday night...Light rain continues across the area this morning ahead of an approaching upper level trough. The trough will continue inland, moving south southeast across Oregon, with coverage of showers increasing across southeast Oregon by 5 AM and southwest Idaho by 10 AM. Showers will diminish from northwest to southeast this afternoon as the low center forms over western California. Precipitation amounts will be light, with the highest amounts up to a tenth or so across the higher terrain. Snow levels remain between 6000 to 7000 feet MSL for up to an inch of snow total on the mountain peaks. Dry, more stable conditions begin on Friday as a weak ridge builds across the area. This setup is favorable for a valley inversion to set up again with plenty of boundary layer moisture and light winds for stratus and fog development Friday morning into Saturday. There remains uncertainty with the coverage, but the best chance for stratus or fog appears to be from the Western Magic Valley through the Upper Treasure Valley Friday morning, redeveloping again on Saturday. Temperatures will be greatly influenced by the stratus clouds, something that I dont think the latest National Blend of Models (NBM) is capturing at the moment. We have adjusted valley temperatures accordingly, but they may still be too warm during the day and too cold at night Friday and Saturday for the lower valleys. Temperatures above the inversion will run about 4 to 8 degrees above normal. .LONG TERM...Sunday through Thursday...Sunday begins with weak flow aloft, with the area slowly transitioning into a different pattern. An upper-level shortwave trough will be traversing the U.S./Canada border, which will sling a cold front south into the area Sunday night/Monday morning. PoPs will be limited to our northern zones and higher elevation. Temperatures will fall to near normal Tuesday onward, helped in part by northwesterly flow aloft behind the trough passage. Snow levels look to fall near 4000 ft MSL at minimum, however, precipitation will be scarce during the minimum. Quickly following this front, long range models agree that an upper-level trough in the Gulf of Alaska will provide another push of moisture mid week. Agreeance on when moisture arrives is varied, providing widespread PoPs Wednesday afternoon through Thursday. && .AVIATION...Areas of MVFR/IFR in low stratus in E Oregon and W-central Idaho, and in isolated/scattered showers in SW Idaho. Precip coverage expanding from the west through midday Thursday. Continued degraded conditions expected, with MVFR/IFR and local LIFR in precip and low ceilings. Mtns obscured. Snow levels 5500-7000 ft MSL. Surface winds: variable less than 10 kt. Winds aloft at 10kft MSL: S to SW 10-20 kt. KBOI...Periodic MVFR with light rain showers and stratus. MVFR ceilings expected to become predominant beginning around 20/12z with shower coverage increasing across southwest Idaho. Rain will taper off Thursday afternoon into evening, with the return of stratus or fog likely Thursday night/Friday morning. Surface winds light and variable. Weekend Outlook...Mountain valley and valley floor low stratus/fog overnight and early morning Friday into Saturday and Saturday into Sunday. Sunday evening, a cold front will be moving into SE Oregon. Precipitation will hold off until early Monday morning. Snow levels 5500-7000 ft MSL. Surface winds: variable under 10 kts. && .AIR STAGNATION...High pressure will develop beginning Friday, with stable conditions persisting through early Monday. Conditions still look to be borderline for air stagnation, with the uncertainty due to mixing heights hovering around or slightly above 2000 feet AGL. However, relatively light winds with a dry, inverted boundary layer will support poorer ventilation in valleys. && .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 SHORT TERM...JDS LONG TERM....CH AVIATION.....CH AIR STAGNATION...JDS