Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
222 FXUS65 KBOI 041046 AFDBOI Area Forecast Discussion National Weather Service Boise ID 346 AM MST Thu Dec 4 2025 .SHORT TERM...Today through Saturday night...Light precipitation will overspread the region this afternoon and evening as a plume of deep moisture arrives in the northwest flow. Sheltered valleys in northern Malheur and Baker counties could see a brief period of light snow or rain/snow mix, but given the afternoon arrival expect any impact to be minimal as temperatures will be above freezing in most spots. In SW Idaho any early snowfall would be limited to the lower Snake Plain this afternoon and upper Weiser basin through early tonight. Similar to SE Oregon any minor accumulation would be limited to colder surfaces. This first round of precipitation will bring 1 to 3 inches of snow above 4kft through Friday morning with liquid amounts of up to 0.15" in the valleys. Friday will see a period of moderate to locally heavy precipitation develop late morning-early afternoon. In the mountains this will translate to snowfall rates of 0.5-1"/hour, bringing 4-8" of additional snow to elevations above 6kft MSL. While the heavier precipitation intensity will likely keep mountain valleys in the snow through Friday afternoon, accumulation will be fighting warmer air (temps in AOA freezing by mid afternoon). The rain/snow elevation line continues to be tricky. By Friday evening as the precipitation lessens expect a broad range in snowfall totals across mtn valleys between 4-5kft MSL. Most mtn valley sites below 5kft MSL see totals (today through Friday) of less than 2 inches, while areas from McCall, New Meadows and Warm Lake to Yellow Pine are looking at 3 to 6 inches. Ensemble probabilities continue to show the tight snowfall gradient in the Long Valley. The NBM5 puts a 60% chance of 4+ inches at McCall with less than a 5% chance at Cascade (HREF shows a similar gradient but is more bullish with 90% chance at McCall). For now will be holding off on any hazard highlights as heavier snow looks localized in mtn valleys, and impacts to road surfaces could be brief given the warming temperatures on Friday. Sites above 6kft (7kft in the Steens and Owyhees) will see 6-12 inches of wet snow through Friday evening. Total liquid (liquid equivalent for the mtns) will see ranges of 0.2-0.5" in the valleys to 0.5-1" in the mountains with locally higher amounts (up to 1.5") along N/W aspects. Periods of light precipitation will continue through Saturday as the region remains locked under northwest flow. The focus of precipitation will be in the mtns (60-80% chance) with lower elevations seeing some drying as precipitation chances drop below 30%. Snow levels will drop to 4500-5500 feet on Saturday and mountains will pick up an additional 1 to 3 inches. Northwest winds will become breezy Friday night into Saturday across SE Oregon and higher terrain of SW Idaho (to include the western Magic Valley) with gusts of 30 to 40 mph. Friday and Saturday are mild with temperatures 5-10 degrees above normal. .LONG TERM...Sunday through Thursday...High confidence that an active pattern will continue over the extended. A strong upper level jet will ride over an upper level ridge and into the Pacific Northwest. Pacific moisture and shortwave disturbances will bring periodic rain and mountain snow. Our area will be on the edge of the storm track for much of the period, and a strong temperature gradient will exist over the area. This increases uncertainty in precipitation amounts and temperatures. However, overall the pattern strongly leans mild and wet with temperatures well above normal and periodic chances of precipitation. A disturbance on Sunday will bring a 20-50% chance of valley rain and a 50-80% chance of mountain rain and snow. Snow levels will be around 4000-6000 feet, lowest in the morning across the north. Precipitation amounts should be light to moderate. Precipitation chances will dip briefly on Monday before increasing once again Tuesday and Wednesday as an atmospheric river moves into the Pacific Northwest. Our area will be on the southern edge of the moisture, resulting in some uncertainty in precipitation amounts. However, moderate to heavy precipitation totals are possible especially in the mountains, and the air mass is expected to be very mild with snow levels pushing up to 6500-8000 feet. By Wednesday, high temperatures are forecast to reach 15-20 degrees above normal. Strong westerly flow will also bring breezy to windy conditions. Forecast confidence is lower on Thursday, but strong, moist westerly flow will persist across the Pacific Northwest, with the potential for additional systems to bring more rain and snow Thursday and beyond. && .AVIATION... Mainly VFR this morning, except for patchy fog near KBNO, mountain valleys, and near the Camas Prairie. Clouds increasing today and gradually lowering, with widespread rain/snow arriving from the northwest this afternoon and evening. MVFR/IFR in rain and IFR/LIFR in snow. Snow levels 2500-3500 feet MSL today, rising to 3500-5000 feet across SW Idaho and 7-8k feet across SE Oregon late tonight. Mountains becoming obscured. Surface winds: S-W 5-15 kt. Areas of low- level wind shear developing tonight. Winds aloft at 10kft MSL: NW 20-30 kt, increasing to 30-50 kt after Fri/00Z. KBOI...VFR through early this afternoon. Increasing clouds with lowering ceilings this afternoon, then rain developing around 22-01Z late this afternoon and continuing tonight. Around a 30% chance of rain mixing with snow through the evening. Borderline MVFR/IFR conditions in precipitation. Surface winds: SE 4-7 kt this morning, becoming variable around 5 kt or less this afternoon. Weekend Outlook...Widespread rain and snow on Friday with snow levels 6-8kft MSL, except 4500-6000 feet across central Idaho. Lighter precipitation is expected Saturday and Sunday with snow levels 4-6kft. MVFR to LIFR conditions in precipitation with mountains obscured. Surface winds SW-NW 5-15 kt, except 10-25 kt with gusts 25-40 kt late Friday into Saturday across higher terrain. && .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 SHORT TERM...DG LONG TERM....ST AVIATION.....ST