393 FXUS65 KBOI 241605 AFDBOI Area Forecast Discussion National Weather Service Boise ID 1005 AM MDT Wed Apr 24 2024 .DISCUSSION...An area of showers has developed over SE Oregon and far SW Idaho in conjunction with a weak mid-level wave. Development with the wave will shift northeastward through early afternoon. Daytime heating and instability will support shower and thunderstorm development across higher terrain later today. Activity will initiate along the OR/NV border and areas south of the Snake Plain in Idaho, then track to the north and east. Gusty winds to 40 mph are possible from showers and storms that develop. Probabilities in the Snake Plain are highest in the Buhl/Castleford/Twin Falls area through early evening (40-60% chance). Forecast for this morning has been updated for shower/thunderstorm potential today. && .AVIATION...Mainly VFR. Scattered showers/virga this morning moving NE, then isolated thunderstorms/showers developing this afternoon and evening, mainly near the Nevada border and in the Magic Valley. Brief MVFR/IFR conditions and mountain obscuration in storms. Gusty and erratic winds up to 30 kt near thunderstorms. Surface winds: variable 10 kt or less, then W-NW 10-15 kt after Wed/21Z. Gusts to 25 kt in the lower Snake Plain tonight as a cold front crosses the area. Winds aloft at 10kft MSL: W 5-15 kt. KBOI...VFR under mid to high level clouds through the period. Isolated virga/showers this morning, moving NE out of the vicinity by Wed/18z. Confidence for afternoon shower/storm development is very low (<5%). Most guidance suggests they should stay well south of the area. Surface winds: variable 6 kt or less this morning, then NW 8-12 kt after Wed/18Z. && .PREV DISCUSSION... SHORT TERM...Today through Friday night...Southwest flow aloft preceding an approaching upper trough near the coast will spread some moisture into the region today. Isolated light rain showers or sprinkles this morning will expand in some areas during the afternoon, becoming scattered in central Idaho and at least scattered (>40 percent) coverage in southern areas near the Nevada border this afternoon. There is enough instability to warrant isolated thunderstorms south of the Snake Plain this afternoon, accompanied by wind gusts to 40 mph. High temperatures will be on par with yesterdays readings, generally in the 60s mountains and 70s valleys. A cold front arrives from the northwest and sweeps through the region tonight. A cooler/stable air mass will spread into the area for drier conditions on Thursday, along with breezy northwest winds. Another upper trough, which will be colder and more moisture-laden, spreads into the area on Friday. Precipitation chances are highest in the mountains for at least a 60 percent chance of measurable rainfall. Precip chances in the valleys generally range from 30 to 50 percent. Snow levels lower to 5500-6500 feet with light snow accumulations possible in the higher mountains. The colder air aloft associated with the trough could provide enough instability to support a slight chance (less than 20 percent) of afternoon thunderstorms. Breezy northwest winds persist into Friday. Temperatures also cool several more degrees with highs slightly below normal. LONG TERM...Saturday through Wednesday...An upper level trough will exit our area to the east on Saturday. A 20-70% chance of showers will continue on Saturday as moisture lingers behind the departing trough, mainly over eastern areas and the central Idaho mountains. Gusty winds will develop behind the trough, especially in the Snake Plain east of Boise. A deep upper level low will move across the Gulf of Alaska over the weekend, placing our area in southwest flow aloft by Sunday. Models then struggle with the progression of this low as it approaches the coast. A majority of ensembles keep the low offshore through the beginning of next week, with a cold front stalling near our forecast area for several days. The location of the front will have a big impact on temperatures, and highs could end up anywhere from 10-15 degrees below normal to 10-15 degrees above normal. Moist southwest flow will keep a 10-50% chance of showers going across our area, with the best chances each afternoon in the mountains. Snow levels are generally expected to remain above 5500 feet, but this will also depend on the progression of the front. Breezy conditions will continue through the period. && .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...DG AVIATION.....JM SHORT TERM...BW LONG TERM....ST |