675 FXUS65 KBOI 302108 AFDBOI Area Forecast Discussion National Weather Service Boise ID 208 PM MST Tue Dec 30 2025 .SHORT TERM...Tonight through Thursday night...Little change to the weather through Wednesday with an upper ridge keeping dry and seasonable conditions locked in place. A persistent surface high over eastern ID will drive easterly winds along portions of the I-84 corridor (Mtn Home-Twin/Jerome and areas in Baker County). After a sunny start, clouds will increase late Wednesday in advance of a low pressure system approaching the CA coast. Light precipitation will develop along the northern NV border Wednesday night, spreading northward on Thursday. With some cold air still trapped across lower elevations of SE Oregon and along the ID/OR border, precipitation could start as snow or a wintry mix in these spots. A slight chance of freezing rain has been added to the forecast, but timing is everything with this and a later start as some guidance is suggesting would remove the FZRA threat for most sites. Snow levels will start between 3-5kft MSL for the e-central Oregon and w-central ID mtns on Thursday, rising to between 6-8kft MSL Thursday night. Mtns below 6kft and interior mtn valleys will see light accumulations through Thursday evening, with the higher amounts (1-3") limited to elevations above 6kft. Thanks to the temperature inversion, highs will be near normal in the valleys and around 10 degrees above normal in the mtns through Thursday. .LONG TERM...Friday through Tuesday...Lingering moisture from a weak, antecedent trough will keep shower activity over west- central Idaho Friday, with snow levels at approximately 7000 feet MSL. Meanwhile, a large, cold cut-off low along the west coast will begin to shift inland Friday. This will enhance southwesterly flow aloft ahead of it and amplify a ridge over the Northern Rockies. Precipitation chances will temporarily dwindle and daytime temperatures will climb to 15 degrees above normal for most areas. The trough will progress northeastward over the weekend, ramping up precipitation chances area-wide (20-30% valleys; 50-60% mountains) along the accompanying cold front mid-day Saturday. Snow levels will gradually lower to 5000-6000 feet Saturday, and to 4000-5000 feet by Saturday night. Subsequent troughs are forecast to arrive inland Sunday and into early next week, spreading additional rounds of precip across the area. These troughs will reinforce southwesterly flow with enhanced orographic lift for the mountains, but will consequently promote shadowing effects for many valleys. The presence of the troughs will lower temperatures a few degrees Saturday, with additional cooling for Sunday and Monday. Models fall out of alignment late Monday/Tuesday, leading to greater uncertainty in temperatures and precip timing. However, continued unsettled conditions are expected. && .AVIATION...VFR, mostly clear. Surface winds: E-SE 5-15 kt. Occasional gusts to 20-25 kt from KMUO to KJER this afternoon. Winds aloft at 10kft MSL: W to SW 5-10 kt. KBOI...VFR. Surface winds: variable or SE 3-8 kt. && .AIR STAGNATION...High pressure aloft will keep a stagnant air mass in place into the end of the week. An increase in daytime winds though the middle Snake Plain east of Boise/Mtn Home area and across the Baker Valley will provide enough mixing to improve conditions so have removed these zones from the ASA. On the other end, have added the w-central ID and Boise mtn zones as mtn valleys are seeing mixing heights drop with the warming aloft. Lower elevations and sheltered valleys will see light winds through Thursday with improving conditions and precipitation Fri/Sat. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Air Stagnation Advisory until 8 AM MST Saturday IDZ011>014-028-033. OR...Air Stagnation Advisory until 8 AM MST /7 AM PST/ Saturday ORZ061-063-064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise SHORT TERM...DG LONG TERM....SH AVIATION.....SH AIR STAGNATION...DG