Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
004 FXUS65 KBOI 090402 AFDBOI Area Forecast Discussion National Weather Service Boise ID 902 PM MST Mon Dec 8 2025 .DISCUSSION...This evening`s 00Z sounding from Boise revealed a very moist air mass for mid December: the measured precipitable water value of 0.66 inches is around the 95th percentile for the time of year. Mild, moist, and strong west-northwest flow aloft will continue to transport moisture into our area through Wednesday, with precipitable water values climbing to around the 99th percentile on Tuesday. The strong flow will aid orographic lift and produce moderate to heavy precipitation amounts in the mountains north of the Snake Basin, where 1-2 inches (locally 3+ inches on higher peaks) of precipitation will fall. Snow levels of 6500-9000 feet will confine snow to the highest peaks, and rivers, creeks, and streams will rise as a result. However, mainstem river flooding is not expected in our area. Light rain will fall off and on through Tuesday in portions of the Snake Plain, especially the Upper Treasure Valley near the foothills, including Boise where some upsloping will occur. The axis of the moisture plume will remain just north of our area, preventing rainfall totals from becoming more impactful across our area. Winds will be breezy, especially in the higher terrain, and temperatures will remain well above normal. && .AVIATION...Precipitation continuing through Tuesday across far E Oregon and much of SW Idaho. VFR expected in light rain. MVFR to LIFR ceilings/vis in heavier rain and high elevation snow, mainly north of Snake Plain. Mtns obscured. Snow levels oscillating between 6.5k-9k feet MSL, lowest to the NE. Low level wind shear threat through Tue AM. Surface winds: SW-SE 5-15 kt. SW gusts to 20-35 kt for higher terrain and open areas, not including Treasure Valley. Winds aloft at 10kft MSL: increasing to W-NW 40-55 kt overnight. KBOI...Persistent light rain through Tuesday evening, but a 90% chance of remaining VFR. Threat of low level wind shear through Tue morning. Surface winds: SE 5-12 kt, transitioning to northerly 3-10 kt Tuesday afternoon. && .PREV DISCUSSION... SHORT TERM...Tonight through Wednesday night...An impressive atmospheric river is lined up across the Pacific Ocean extending past Hawaii and is impacting the Pacific NW. Precipitation will become widespread north of a line from Burns OR to Jerome ID late this afternoon and last through Tuesday night. This will bring 1-2 inches of liquid equivalent precipitation to the central ID mountains. Heavier precipitation will be just north of our area. Rivers, creeks and streams will see notable rises over the next few days. Snow will be confined to the highest peaks above 7000-8000 feet. LONG TERM...Thursday through Monday...The active weather takes a break Thursday. The ridge supporting the atmospheric river will move inland, pushing most of the moisture north of our area. Precipitation tapers off through the day Thursday with only a 20-30% chance of precip in the mountains that evening. Winds also come down as the strong flow aloft shifts north with the AR. Temps remain 10- 15 degrees above normal, with partly cloudy skies each day through Sunday. The main hazard Thursday through Sunday will be mixing heights less than 2 kft AGL in the afternoons, an indicator of inversion development. Saturated soils from the recent rain will make fog and low stratus likely, especially if a strong inversion forms. Thursday and Friday would be the warmest days with a slight cool down Saturday and Sunday with highs dropping from near 60 in the Snake Plain to the lower 50s. Low confidence in temperature forecasts as the effect of inversions and fog/stratus tend to not be captured well by models. Speaking of models, after Sunday there is disagreement in the arrival of our next system. Most if not all hint at the ridge weakening and the storm track moving back south over the area, but differ on when that first storm moves through. Monday would be the earliest shot at our next round of precipitation, with chances increasing further into next week. && .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...ST AVIATION.....SH SHORT TERM...KA LONG TERM....JM