Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
922 FXUS65 KBOI 031549 AFDBOI Area Forecast Discussion National Weather Service Boise ID 949 AM MDT Fri May 3 2024 .DISCUSSION...Main ideas continue to be sunny and warmer wx today, then increasing clouds and southeast/southwest winds and warmer again on Saturday ahead of an approaching north Pacific cold front. Moderate to heavy rain late Saturday/Saturday night as the cold front moves through, then gusty west winds and much colder wx Sunday with lighter showers of rain and snow. Also, a 20 percent chance of thunderstorms in eastern-most Idaho zones Saturday afternoon and again Sunday afternoon. We`re considering a Wind Advisory for the central Snake Basin and southeast Oregon on Saturday, otherwise current forecast is on track. See "Prev Discussion" (below) for details. && .AVIATION...VFR. Local valley fog/stratus has mostly cleared, but IFR conditions may still exist in isolated mountain valleys through Fri/18Z. Mountains will see scattered to broken cumulus field with bases 3500-5500ft AGL. Surface winds: variable or NW 5-15 kt, then S to SE 10-20 kt this afternoon. Winds aloft at 10kft MSL: Variable <10 kt, becoming S 10-20 kt Fri afternoon. KBOI...VFR and clearing Friday. Light NW winds, becoming SE 10-15 kt Friday afternoon. Winds are set to increase significantly early Sat morning to SE 20-25 kt with gusts to 30-40 kt. Weekend Outlook...Widespread precipitation moves into SE Oregon mid- morning Saturday, then into SW Idaho Saturday afternoon and will continue across the region through Sunday. A 20% chance of thunderstorms Saturday afternoon in s-central Idaho. Snow levels 6000-7000 ft MSL, lowering to 4000-5000 ft Sunday. IFR and widespread mountain obscuration Saturday night and Sunday. Surface winds: SE 15-25 kt with gusts 30-40 kt Saturday afternoon, W 5-15 kt with gusts to 20-30 kt Sunday. && .PREV DISCUSSION... SHORT TERM...Today through Sunday night...Any lingering showers wrapping around an exiting upper trough will dissipate by mid- morning. The exiting trough is replaced by an upper ridge this afternoon, resulting in dry weather and temperatures 5-10 degrees warmer than yesterday. Upstream, a deep Pacific low will approach the NW coast on Saturday. This system will be punctuated by heavy precipitation and gusty winds as it pushes into the region late Sat/Sun. The winds will increase out of the S-SE on Saturday in advance of the low. Widespread sustained winds of 20-30 mph with gusts to 40 mph are expected. Locally stronger winds could set up over SE Oregon Saturday and in portions of the Snake Plain east of Boise that would require headlines. A band of heavier precipitation will form ahead of a cold front that will push into SE Oregon Saturday afternoon, then cross into SW Idaho by evening. Marginal instability and surface energy will support a 15% chance of thunderstorms over s-central Idaho Saturday. Storms that do form will have a favorable shear profile and could become strong. The front will bring a wind shift to the NW Saturday night that will be reinforced by flow aloft on Sunday. Precipitation will continue on Sunday as it wraps around the low center which is forecast to track through northern NV. The probability for precipitation totals of over 0.25" has increased to greater than 80% across SE Oregon and SW Idaho through Sunday. The axis of heavier precipitation remains near the OR/ID border where the chance of exceeding an inch of liquid through Sunday is 15-30%. Snow levels ahead of the front will rise to 6-9kft Saturday evening, falling quickly behind the front Sunday morning. This could bring accumulating snow to SE Oregon as snow levels briefly drop to around 3000 feet early Sunday. Otherwise much of the accumulating snow is above 5500 after the frontal passage. Precipitation continues in the mountains through Sunday night while valleys trend drier. LONG TERM...Monday through Friday...Northwest flow continues in the wake of the exiting trough on Monday. Models show trailing shortwave energy that will keep a chance of showers over the region through Tuesday. An upper ridge will build along the coast Wednesday, gradually folding inland through Friday. Deterministic and ensemble solutions are in good agreement with with this pattern change. Afternoon instability will support a 15-30% chance of showers over the mountains while lower elevations remain dry. Temperatures through Wednesday are 10-15 degrees below normal, warming to near normal Thur/Fri. && .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...LC AVIATION.....JM SHORT TERM...DG LONG TERM....DG