FXUS65 KBOI 211147 AFDBOI Area Forecast Discussion National Weather Service Boise ID 547 AM MDT Tue Apr 21 2026 .UPDATE...Updated aviation discussion. && .KEY MESSAGES... - After a dry and warm afternoon today, a strong cold front arrives this evening with gusts to 45 mph, increasing showers, and isolated thunderstorms. - Much cooler on Wednesday with widespread precipitation, isolated thunderstorms, gusty winds, and snow levels lowering to 4500 to 5500 feet. - Precipitation totals of 0.5 to 1.5 inch in the mountains, 0.25 to 1.0 inch in the valleys. Snow amounts of 6 to 12 inches above 6000 feet. - Cool, but gradually warming, Thursday through early next week with precipitation chances persisting mainly over the higher terrain. && .SHORT TERM /Through Thursday Night/... Issued 259 AM MDT TUE APR 21 2026 Today will be the last warm and mostly dry day before the return of much cooler and wetter conditions. Southerly flow ahead of a deep upper low off the northern California coast will once again bring temperatures 15-20 degrees above normal on the Idaho side. This will push highs into the upper 70s to lower 80s at lower elevations. However, an advancing strong cold front associated with the low will bring cooler temperatures and increasing showers to southeast Oregon this afternoon. Southerly winds this afternoon ahead of the front will gust to 25-40 mph. The front will sweep through the Treasure Valley early to mid evening and through the Magic Valley late evening. Gusts to around 45 mph are expected along the front along with scattered showers and isolated thunderstorms. The main upper low will rapidly move inland tonight into Wednesday, with the low center moving directly over the area overnight into Wednesday morning. Convergence and deformation near the low center will promote widespread precipitation behind the front, initially moving into southeast Oregon this evening and spreading into southwest Idaho overnight into Wednesday morning. There will be enough instability for thunderstorms to continue overnight across east-central Oregon and west-central Idaho. As the low tracks northeast Wednesday afternoon and evening, moist west to northwest flow will continue to bring showers to the area. A low threat for thunderstorms will also linger across the mountains. Precipitation across the central Idaho mountains and adjacent windward valleys (including the Treasure Valley, especially near the foothills) will be aided by upslope flow. Precipitation totals through the event will be significant, with most lower elevations picking up 0.25-1.0 inch of rain. In the Treasure Valley, there is a 10-30% chance of an inch of rain or more, with a 40% chance near the foothills. In the mountains, 0.50-1.50 inch of precipitation is expected, with closer to 2 inches possible in locations favored by northwest flow, such as Bogus Basin. High temperatures will be 20-30 degrees cooler Wednesday than today as the low moves in. Snow levels will fall to 4500-5500 feet by Wednesday morning, lowest across southeast Oregon. Heavy mountain snow accumulations of 6-12 inches are expected above 6000 feet, with locally higher amounts. Mountain valleys above 4500 feet will mix with or change to snow, but any accumulations should be less than an inch. Wind gusts on Wednesday of 25-40 mph will be common, locally up to 45 mph. Another low will drop into the area from the north on Thursday, but will not be nearly as strong as the first low. The track will favor continued light mountain precipitation with a 20% chance or less of precipitation south of the Snake Basin. The low will keep cool temperatures and gusty winds in place on Thursday. && .LONG TERM /Friday through Tuesday/... Issued 259 AM MDT TUE APR 21 2026 A broad upper-level trough over southern Canada and the northern U.S. will maintain a cool northwest to west flow across the region Friday through Monday. This pattern will keep high temperatures a few degrees below seasonal norms, with daily shower chances (10-30%) persisting over the higher terrain. Snow levels will generally range from 4500-6500 ft MSL. Brief drying conditions alongside a slight warming trend are expected by Tuesday as the upper low gradually departs toward the east. && .AVIATION /12Z Tuesday through Wednesday/... Issued 546 AM MDT TUE APR 21 2026 VFR through midday. Scattered showers/t-storms late afternoon, becoming numerous in the eve with a strong cold front. Precip continues overnight into Wed with snow levels dropping to 4500-5500ft MSL. Conditions worsening overnight/Wed: periods of low VFR-IFR in valley rain, and IFR-LIFR in mtn snow. Mtns becoming obscured. Surface winds: SW-SE 5-15 kt, with PM gusts to 20-30 kt. Winds shift to SW-NW 15-30 kt with 25-45 kt gusts during frontal passage, then weaken behind front. Winds aloft at 10kft MSL: S-SW 15-30 kt, shifting to W 20-40 kt late tonight. KBOI...VFR through this afternoon. Showers developing after Tue/23Z ahead of a cold front, with a 20% chance of lightning. Cold front passage and wind shift between Wed/02Z-03Z. Rain will become continuous after Wed/06Z, with MVFR conditions during Wed morning hours. Surface winds: S-SE winds 5-15 kt. Shifting to SW-NW 10-20 kt, with a period of 30-40 kt gusts during frontal passage. && .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 AVIATION.....SH SHORT TERM...ST LONG TERM....SH