FXUS65 KBOI 152011 AFDBOI Area Forecast Discussion National Weather Service Boise ID 211 PM MDT Tue Oct 15 2024 .SHORT TERM...Tonight through Thursday night... KEY MESSAGES... * Dry and calm weather for the rest of today and tonight. * Sharp weather change on Wednesday bringing showers, gusty winds, and a significant cooling trend through Thursday night. For the rest of today through tonight, southwest flow aloft will keep us 10-20 degrees above normal, with some mid-high clouds and typical winds. Valley highs have already reached the upper 70s/lower 80s. Wednesday a shortwave and associated cold front will move through the area ahead of a deep upper low pressure system. This will bring a line of showers ahead of the front, passing through SE Oregon in the morning and SW Idaho in the late morning/afternoon. A 90% chance of precipitation exists during a 24-hr period through Wednesday for most of the area with this line. Wind gusts with the frontal passage will be 20-25 mph in general, higher along ridges. Convection will initiate behind the front in the colder airmass, though the depth of instability appears to shallow for a meaningful chance of thunder. SPC has an area of general thunder over our area to account for a stray pulse or two, though chances are too low (<10%) for us to include in the forecast grids. Thursday, after the cold front and as the upper low system moves closer overhead, temperatures drop to about 5 degrees below normal. Winds stay gusty and showers remain possible through Thursday night, with an accumulation forecast of 0.1-0.2 inches of rain for lower elevations and 0.3-0.6 for mountain valleys and ridges. Confidence in the exact rainfall forecast for valleys is low, given spread between models and the lack of orographic effect outside of foothills and mountains. Between a dusting and 0.5 inches of snow are possible for elevations between 5000-7000 ft, with 0.5-2.5 inches possible along ridges above 7000 ft. Mountain valleys may see fog develop Thursday morning .LONG TERM...Friday through Tuesday...Dry but much cooler conditions Friday through the remainder of the long term. Wind gusts of 25-30 mph are expected Friday morning between Mtn Home and the Magic Valley. Weakening slightly in the afternoon as forcing reduces. Morning lows Friday through the weekend will be 5-10 degrees below normal, down to freezing for many valley locations. The chance of morning low temps at or below freezing is 40-50% for the Treasure Valley both Friday and Saturday. In the Magic Valley chances are 80-90%. There is some uncertainty beyond Sunday on the progression of an upper low pressure system. Deterministic models have been switching up every few runs on whether it impacts us or not. The general consensus is carrying a 20-40% chance of precipitation beginning Sunday night through Monday evening, with a 5-15% chance after Monday. && .AVIATION...VFR under clear skies. Reduced visibility from wildfire smoke in some central Idaho mountain valleys. Breezy winds and showers moving in tomorrow with a front around 16/12Z near KBKE-KBNO, then into KMYL-KONO-KEUL-KBOI by 16/19Z. Surface winds: SE-SW 5-10 kt, then NW 10-15 kt with gusts 20-30 kt with the frontal passage by 16/22Z. Winds aloft at 10kft MSL: SW 20- 30 kt. KBOI...VFR through today, then rain showers beginning at 16/19Z tomorrow with variable surface winds 3-5 kt, becoming NW 5-10 kt by 16/14Z. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise SHORT TERM...JM LONG TERM....JM AVIATION.....SA