Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
924 FXUS65 KBOI 031645 AFDBOI Area Forecast Discussion National Weather Service Boise ID 945 AM MST Wed Dec 3 2025 .DISCUSSION...Fog and low stratus lingering across portions of the area this morning including the Harney Basin of Oregon and the Magic Valley of Idaho. Consensus is that this stratus and fog will dissipate/retreat through the day. Increasing high clouds today ahead of an approaching Pacific system. Precipitation chances up area-wide by Thursday afternoon and lingering into the weekend. The current forecast handles this trend well, no updates planned this morning. && .AVIATION...Areas of IFR/LIFR fog/low stratus this morning, mainly in the Magic Valley and along the Nevada border. Conditions improving this afternoon. Otherwise, VFR conditions today. Surface winds: W-NW 5-10 kt. Winds aloft at 10kft MSL: N 10-20 kt. KBOI...Mainly VFR. A 20% chance of IFR/LIFR fog/low stratus this morning as winds become light, with a higher chance along the foothills. Surface winds: light and variable this morning, becoming NW around 5 kt this afternoon. && .PREV DISCUSSION... SHORT TERM...Today through Friday night...The next 24 hours will see dry and stable conditions over the region as an upper ridge builds in aloft. With this will come the ebb and flow of fog and low stratus. For now Satellite and forecast trends would support the focus of fog/stratus to develop across portions of the Snake Plain (Boise eastward) and higher terrain to the south and west. Don`t expect any widespread dense fog and there is still enough northwest flow aloft to support erosion of the fog/stratus this afternoon. Clouds increase tonight and light precipitation will develop from northwest to southeast on Thursday as deep moisture rides over the Pacific ridge. Snow levels will start off between 2-3kft MSL, so light snow is possible down to valley floors. Given the afternoon timing and light intensity, accumulations will be less than an inch across the region through the afternoon. The precipitation intensity will pickup across the mtns Thursday night into Friday as mid-level winds (~10kft MSL) increase to 30-50 kt. Snow levels will also rise through the period, more so across SE Oregon where they reach 5-6kft MSL Friday morning, and 6-8kft by Friday evening. Snow levels are slower to rise across the w-central Idaho mtns, staying between 4-5kft through Friday, rising to between 5-6kft Friday night. While this has bumped up deterministic snow amounts for some higher mtn valley sites like McCall it will only take small change in the rain/snow elevation to swing snow totals through the forecast period. This is evident in the NBM snowfall probability forecasts which carry an 80% chance of 2+ inches at McCall through Saturday morning, but only 30% chance of 2+ inches at Cascade. Push that threshold up to 4" and the probabilities drop to 40% and <5% respectively. Sites above 6kft, where it stays all snow, can expect to see 5-10" from Thursday night through Saturday morning. Liquid (equivalent) totals will hold under a quarter inch at lower elevations with widespread 0.4-0.8" amounts in the mountains and locally up to 1" across higher peaks. LONG TERM...Saturday through Wednesday...An active pattern will continue over the extended as the jet stream rides over an upper level ridge and into the Pacific Northwest. Confidence is high that this overall pattern will persist through the period. Pacific moisture and shortwave disturbances will bring periodic rain and mountain snow to the area. However, confidence in timing and amounts is lower. This is due to our area being situated on the southern edge of the storm track. Small changes in the amplitude of the ridge will have large impacts in our area, with a stronger ridge pushing systems to our north, and a weaker ridge allowing for widespread and heavier precipitation amounts to move into our area under strong westerly flow. Currently, the highest chance of precipitation is on Saturday (60- 90%), then trends lower (30-70%) on Sunday with the highest chances in the northern mountains. Snow levels will remain high at around 5000-7000 feet, lowest in the north, resulting in most areas seeing rain with snow limited to higher peaks. Precipitation amounts over the weekend should be light to moderate. Temperatures will average around 10 degrees above normal, and winds will be breezy. Ensembles are in agreement about the ridge keeping our area mostly dry on Monday. Uncertainty increases on Tuesday and Wednesday as an atmospheric river moves into the Pacific Northwest. At least some moisture is favored to make it into our area (especially across the north), but how much will be determined by the strength of the ridge. Mild temperatures will continue, reaching 10-15 degrees above normal for early to mid December. && .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...MC AVIATION.....CH SHORT TERM...DG LONG TERM....ST