Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
723 FXUS65 KBOI 291630 AFDBOI Area Forecast Discussion National Weather Service Boise ID 1030 AM MDT Mon Apr 29 2024 .DISCUSSION...An unseasonably cool upper level trough is moving onshore this morning into western OR and WA. This system will bring a cold front through the area today, with snow and graupel showers mainly north of a line from Burns OR to Boise ID this afternoon. The showers will be enhanced over the mountains, with a slight chance of thunderstorms this afternoon and evening. The upper level trough will remain over the area through Wednesday with temperatures around 10-15 degrees below normal. Snow showers containing graupel possible on Tuesday afternoon and again on Wednesday afternoon due to the cold air aloft and high sun angles. Sensitive plants in the Snake Basin should be covered tonight and tomorrow night as temperatures will be at or below freezing in the lowest valleys. && .AVIATION...VFR. Scattered MVFR showers across the north (KBKE- KMYL) through Mon/18Z, becoming widespread in the north and isolated to scattered elsewhere after Mon/18Z. Mountains obscured. Snow levels 4000-5500 ft MSL, lowering to 2500-3500 ft MSL by Tue/06Z. Surface winds: Increasing to W 15-25 kt with gusts to 30 kt this afternoon, peak gusts of up to 40 kt near MUO. Winds aloft at 10kft MSL: W 25-35 kt. KBOI...VFR with increasing clouds. Slight chance (less than 20 percent) of -SHRA between Mon/18Z and Tue/00Z. Surface winds: NW 12- 15 kt increasing to 17-22 kt with gusts to 25-30 kt this afternoon. Winds decrease to 8-12 kt around Tue/04z and switch to SE around Tue/10z. && .PREV DISCUSSION... SHORT TERM...Today through Wednesday night...An upper level trough will move through the region today, bringing a cold front through the area. This front will bring much colder temperatures, gusty westerly winds, and showers. The front looks to move through southeast Oregon by early afternoon, and then through southwest Idaho by late afternoon. The best chance for showers will be over the higher terrain in Baker County, OR, near the ID-NV border, and the West Central Mountains (70-80% chance). However, there is also a low chance (10-20% chance) for showers over the Treasure Valley on Monday afternoon. Models show the best instability and heaviest showers over the Central ID Mountains and Baker County, OR, but there is still sufficient instability across the region that would allow for a stray thunderstorm near the NV border and over the Lower Snake Plain. Confidence is low, but it has been added to the forecast for this afternoon. Winds will be highest in the Lower Snake River Plain today and tomorrow afternoon, but hi-res models have trended winds down quite a bit since last night. Winds will still be gusty, especially during the frontal passage today, so the wind advisory remains in effect for those zones. The colder air mass will lower snow levels quite a bit later today, especially across the northern portions of our CWA. The West Central/Boise Mountains and Baker County will see snow levels lower to 3000-4000 feet overnight, so any precipitation by the evening and overnight will fall as snow. Limited moisture will reduce accumulations, but an inch or two is possible over the higher terrain by early Tuesday morning. As the low exits to the east, a weak ridge will build into the region on Wednesday, bringing warmer and drier conditions. Temperatures will still be about 5-10 degrees below normal today through Tuesday, but the ridge will usher in a warming trend for the end of the short term period. LONG TERM...Thursday through Monday...Latest models are in poor agreement, especially next weekend, leading to substantial uncertainty in the forecast. There are two main features of interest. The first is a compact low pressure system that is progged to move through from the northwest Thursday into Friday. The track of the low differs among the models...some are slower and direct more showers to the area, while others are faster or show the bulk of the showers to our north. Most of the members favor a more northerly track, resulting in a 15-30 percent chance of showers across Baker County and central Idaho Thursday and Friday. Breezy conditions are expected both days, along with near-normal temperatures. The second feature of interest is another Pacific low that is either progged to move through our area over the weekend, or remain near the west coast. Therefore, there is a 10-20 degree spread in temperatures. The ensemble blend favors a warmer/wetter solution with temperatures several degrees above normal while maintaining a 15-40 percent chance of showers over the weekend and into early next week. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Wind Advisory until 7 PM MDT this evening IDZ014-016-028. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...KA AVIATION.....JM SHORT TERM...SA LONG TERM....BW