463 FXUS65 KBOI 301013 AFDBOI Area Forecast Discussion National Weather Service Boise ID 313 AM MST Tue Dec 30 2025 .SHORT TERM...Today through Thursday night...Broad ridge of high pressure aloft over the interior western US now looks like it will continue through Friday night before shifting eastward into the Plains states. That means a continuation of a surface- based inversion even as the air mass moistens from the south beginning Thursday (New Years Day). As these inversions age they typically settle into the Lower Treasure Valley and Baker County and those areas should be the last to mix out. Other valleys should gradually warm beginning New Years Day. Starting Wednesday a Pacific upper low off southern California near 30N/128W will move closer to the coast while a deeper Pacific trough moves eastward to 140W. Southwesterly flow aloft will advect moisture into our CWA leading to light rain beginning late Wednesday night in our southern CWA and spreading northward over all zones New Years Day. Persistent cold air may allow freezing rain in the coldest valleys of eastern Baker County but that's a difficult call this far ahead. Elsewhere, snow level will start near 5000 feet north to 6200 feet south Mew Years Day and rise to 6500 feet north to 7500 feet south Friday. Total precipitation New Years Day through Friday night should range from .10 to .25 inch in southern areas, and .25 to .60 inch in the Idaho north of the Snake Basin and in Baker County/OR. Winds will not be significant except near Jerome ID where northeast winds will continue 15 to 25 mph. .LONG TERM...Friday through Tuesday...A brief drier period is forecast Friday night before the Calif upper trough comes inland with more pcpn and also wind for our CWA Saturday. The inversion and air stagnation will end at that time, and moist, mild, and breezy weather will continue through Saturday night. We see a drier period Sunday and Monday, then wetter again Tuesday when the stronger Pacific trough moves onto the coast, with more troughs and pcpn to follow. && .AVIATION...VFR except for patchy fog/low stratus in mountain valleys until 17Z. Surface winds: E-SE 5-15 kt. Winds aloft at 10kft MSL: W 10-15 kt. KBOI...VFR. SE surface winds 5 to 10 kt. && .AIR STAGNATION...With the upper level ridge now expected to persist the Air Stagnation Advisory has been extended until 5 AM MST Saturday. Until then daytime mixing heights will be 2000 feet AGL or lower. On Saturday, increasing wind and pcpn should fully mix out the inversion and end the air stagnation. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Air Stagnation Advisory until 5 AM MST Saturday IDZ012-014-016-028-033. OR...Air Stagnation Advisory until 5 AM MST /4 AM PST/ Saturday ORZ061>064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise SHORT TERM...LC LONG TERM....LC AVIATION.....LC AIR STAGNATION...LC