Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
359 FXUS65 KBOI 010328 CCA AFDBOI Area Forecast Discussion...CORRECTED National Weather Service Boise ID 928 PM MDT Tue Apr 30 2024 .DISCUSSION...An upper level shortwave is moving over southcentral WA into NE Oregon toward the Blue Mountains tonight. The system will track southeastward overnight and into the central ID mountains by Monday morning. This system will bring snow showers as it passes through. Current forecast and ensembles not resolving mesoscale features of this system, so have adjusted the forecast to add a mention of rain and snow showers (15 percent chance) overnight into midday Wednesday. Some of these showers have the potential to produce snow accumulations 1 to 2 inches as they pass through. Forecast has been updated to add mention of showers in the Treasure Valley. Cold air aloft, with -33C at 500mb on Wednesday morning through afternoon will fuel showers during the afternoon. Have added mention of showers on Wednesday afternoon across much of the area, with the exception of southcentral OR, where warmer air aloft will keep conditions stable. && .AVIATION...Mainly VFR. Isolated to scattered rain/snow showers north of KBNO-KBOI-KSUN line. Snow showers obscuring mountains and producing brief MVFR conditions. Snow levels around 3000-4000 ft MSL, lowering about 500 ft overnight. Surface winds: W-NW 5-15 kt, with gusts to 20-25 kt through Wed/05z near KTWF/KJER. Winds aloft at 10kft MSL: W to NW 15-25 kt. KBOI...VFR with scattered/broken clouds 6000-9000 ft AGL. Isolated showers will pass north of terminal overnight, with a 15% chance of showers entering the 10 mile vicinity. Snow levels as low as 3000- 3500 ft MSL this evening, lowering to 2700-3300 ft MSL by Wed morning. Generally NW 5-15 kt with gusts to around 20 kt through 04Z. && .PREV DISCUSSION... SHORT TERM...Tonight through Thursday night...Showers have begun ahead of the approaching shortwave, primarily in Baker County and the West Central Mountains of Idaho. Snow has been spotted as low as 2600 feet near Cambridge, Idaho, but significant accumulation is only expected above 4500 feet. High-resolution models predict showers to stay north of a line stretching from Burns to Ontario to Stanley throughout this afternoon and evening. There`s a possibility of weaker showers in the Lower Treasure Valley near Caldwell and Nampa, but any precipitation is unlikely to reach the ground. The upper-level jet over our southern forecast area will bring breezy winds overnight, along with the chance for stronger showers producing lightning strikes and graupel. While there`s a potential for mixed precipitation down to 2500 feet, surface temperatures should stay above freezing, limiting significant accumulation to elevations above 4500 feet. Early Wednesday, a weak cold front will pass through, maintaining increased winds in the area, especially affecting the Western Snake River Plain into the afternoon. This could help keep min temperatures just above freezing especially in the Lower Treasure and western parts of The Upper Treasure Valley tonight. Gusty winds may reach advisory levels in the Western Magic Valley and Camas Prairie, although the likelihood is currently estimated at about 30%, lower than earlier forecasts. Thursday will offer a brief respite from these systems, with dry conditions but below-normal temperatures persisting. Northwesterly flow will keep winds elevated in the valley. LONG TERM...Friday through Tuesday...A weak ridge will bring brief dry conditions Friday. Upper level winds will quickly turn southwesterly as the next low pressure system approaches the PacNW Friday/Saturday. Temperatures will rise to near normal both Friday and Saturday from the brief high pressure and southerly influence. However, models become out of alignment on the path of this incoming low this weekend and create uncertainty in the forecast. Approximately 50% of latest ensemble members carry the low farther south into California, keeping temperatures over E Oregon and SW Idaho slightly warmer while slowing down the arrive of showers/thunderstorms over the area. Meanwhile, the rest of the ensemble solutions track the low right overhead, supporting notably cooler temperatures and an earlier arrival of showers/thunderstorms. As a result, the current forecast for the weekend has an influence of cooler temperatures overall, along with 40-60% chance of precipitation with high uncertainty in snow levels. Thereafter, models keep a cool and showery northwest flow over the forecast area early next week with slightly below normal temperatures anticipated. && .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 DISCUSSION...KA AVIATION.....SP SHORT TERM...JDS LONG TERM....SH