FXUS65 KBOI 121025 AFDBOI Area Forecast Discussion National Weather Service Boise ID 325 AM MST Fri Dec 12 2025 .SHORT TERM...Today through Sunday night...High pressure will continue to build in over the Intermountain West this weekend. A surface temperature inversion will develop across the region, with stagnant air becoming a concern in sheltered valleys in southeast Oregon and along the Snake River Valley tomorrow through at least Monday morning. Low mixing heights and limited vertical mixing will trap pollutants and create a low risk for valley fog, especially overnight. Temperatures will remain above normal throughout the weekend, with lower temperatures anticipated at valley floors while midslopes will see temperatures up to 20 degrees above normal today and Saturday. A record high temperature was tied yesterday in Boise, with 63F reached. Boise metro temperatures will be slightly cooler today, but still in the upper 50s (anywhere from 16-18 degrees above normal). A weak shortwave trough will move into California on Sunday, bringing increasing cloud cover and a slight uptick in southwest winds near the Nevada border. This won't be enough to reduce the inversion, but might bring slightly cooler temperatures on Sunday. LONG TERM...Monday through Friday...Westerly flow will begin to strengthen Monday associated with the next moist trough, and therefore will shunt the upper ridge toward the south and east. Precipitation chances will ramp up across the forecast area late Monday as the first wave of Pacific moisture arrives with this trough. Temperatures will initially stay mild Monday and Tuesday as the colder airmass remains to the north, supporting relatively high snow levels at approximately 7000 feet or higher. These mild conditions will not last for long, since a prominent and windy cold front is forecast to move through east Oregon and southwest Idaho Tuesday evening into Wednesday. This front will be accompanied by a potent atmospheric river plume, spreading notable precipitation across the region. Max temperatures will plummet by approximately 10 degrees for Wednesday, with snow levels also lowering to 3500-5000 feet MSL. While precipitation will become likely area-wide, this flow will most favor the higher terrain of west- central/central Idaho. Thereafter, models disagree on the positioning of the polar jet stream beginning late Wednesday and beyond, which decreases forecast confidence in temperatures/snow levels for the rest of the week. However, ensembles suggest that a fairly persistent plume of Pacific moisture will continue to pummel the Pacific Northwest throughout the rest of the week. As a result, significant precipitation totals are possible across the mountains throughout next week, reaching over an 1" of new liquid equivalent over the west-central and central Idaho terrain. Depending on the oscillation of snow level during these series of moisture pushes, snowfall totals could reach 1 to 2 feet for higher elevations during this extended period, as well. && .AVIATION...VFR, except mountains obscured around KBKE-KMYL-KSNT in low ceilings. Patchy valley fog possible this morning, but confidence is low. Conditions improving this afternoon. Surface winds: variable around 10 kt or less. Winds aloft at 10kft MSL: NW 20-35 kt. KBOI...VFR. SE winds 5-10 kt, then briefly N-NW or variable around 5 kt in the afternoon. Weekend Outlook...Mostly VFR with low confidence in low stratus and fog in sheltered valleys each morning. Light winds. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Air Stagnation Advisory from 5 AM early this morning to 5 AM MST Monday IDZ012-014-016-033. OR...Air Stagnation Advisory from 5 AM MST /4 AM PST/ early this morning to 5 AM MST /4 AM PST/ Monday ORZ061>064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise SHORT TERM...SA LONG TERM....SH AVIATION.....SH