Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
514 FXUS65 KBOI 201624 AFDBOI Area Forecast Discussion National Weather Service Boise ID 924 AM MST Thu Nov 20 2025 .DISCUSSION...At 9 AM MST radar showed a band of light rain in ID extending from Council through Mountain Home to eastern Owyhee County. The band was shifting northeastward. This band proved wetter and better organized than forecast yesterday and supplied more moisture for potential fog in the valleys the next several mornings as an inversion sets up. Current forecast already has fog but it may be increased in the afternoon package. Meanwhile, the main frontal band in OR last night was dissipating in OR but will stay active in Calif near a southward-moving upper low. Current forecast still has light rain showers in our CWA today. Latest models suggest fewer showers now but not enough to update. && .AVIATION...IFR-VFR in low stratus and in a precip band that is moving through central Idaho. Precip becomes more isolated this afternoon and continues in the ID mtns and S-central ID with snow levels at 5-7 kft MSL. Fog is lingering behind the precip band, and has been patchy in the lower Treasure Valley, LIFR is possible through early this afternoon. Surface winds: light and variable. Winds aloft at 10kft MSL: S-W 5-15 kt. KBOI...VFR with low ceilings near MVFR, precip has moved east. Fog in the area is unlikely to make it into the vicinity this morning, but fog/low stratus may return tonight with a 35% chance of LIFR. Surface winds light and variable. Weekend Outlook...Mountain valley and valley floor low stratus/ fog overnight and early morning Friday into Saturday, and again Saturday into Sunday. On 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 kt. && .PREV DISCUSSION... 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 don`t 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. Agreement on when moisture arrives is varied in the Wednesday afternoon through Thursday time frame. && .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.....JM SHORT TERM...JDS LONG TERM....CH