Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
773 FXUS65 KBOI 022029 AFDBOI Area Forecast Discussion National Weather Service Boise ID 229 PM MDT Thu May 2 2024 .SHORT TERM...Tonight through Saturday night...A dynamic weather pattern is unfolding over the next few days, characterized by a shortwave passage today followed by the arrival of a robust cold core low pressure system over the weekend. This setup indicates a high potential for significant rainfall during the upcoming weekend. The shortwave is currently tracking east-southeast, expected to reach southeast Oregon later today and southwest Idaho tonight. Convective activity, including showers and thunderstorms, has already commenced across southeast Oregon, with further development anticipated south of the Treasure Valley through this evening. While eastern portions of the Upper Treasure Valley and Western Magic Valley may experience some activity later today, the majority of the Treasure Valley should remain dry until late tonight. Showers and thunderstorms could bring brief heavy rain, along with graupel below 4000 feet. Higher elevations may see a transition to graupel or snow with minimal accumulation. As the shortwave moves out of the region tonight, wrap-around showers from the east will persist across the West Central and Boise Mountains, extending into much of the Western Snake River Plain into early Friday. Friday itself is expected to be warm and dry as a weak ridge builds over the area, with temperatures reaching the mid to upper 60s in the lower valleys. The subsequent weather system, characterized by a deep closed low, will sweep across the forecast area late Saturday. A substantial precipitation band will form along the cold front preceding the low, spreading from southeast Oregon early Saturday to southwest Idaho by late afternoon. Recent model runs suggest increased precipitation amounts, with a 60-80% probability of 0.25" or more of liquid across much of the area, and a 10-20% chance of exceeding 1.00. Snow levels are expected to remain elevated above 6500 feet, limiting snowfall to the highest mountain peaks. Winds will intensify on Saturday, initially from the east as the low draws in air, then shifting to the northwest behind the cold front Saturday night. Sustained winds of 20-30 mph, with gusts of 30-40 mph, are anticipated ahead of the front along the I-84 corridor from Twin Falls to Baker City, as well as over higher open terrain in southeast Oregon. Additionally, there is a potential for thunderstorms ahead of the cold front across south-central Idaho on Saturday afternoon, with forecasted surface temperatures in the low 70s and favorable atmospheric conditions supporting a few stronger thunderstorms. .LONG TERM...Sunday through Thursday...Unsettled weather from a deep low continues to dominate the earlier parts of the long- term forecast. Sunday`s max temp drops 10-20 degrees below normal under the very cold airmass, though the min temps are `only` 5 degrees below normal. A 60-80% chance of precipitation exists throughout the area late Sunday, dropping to 20-40% in lower valleys and 50-70% for higher elevations early Monday through later Tuesday. There is a brief peak in activity Monday evening as an embedded upper shortwave is carried through in the northwest flow aloft. Late Sunday through Tuesday, lower elevation liquid precip totals will be 0.05-0.20 inches. Higher elevation liquid totals of 0.3-0.5 inches will likely fall as 1-6 inches varying greatly with elevation as snow levels are forecast to be 4000-5000 ft MSL. There is a very small chance (<5%) that parts of the Snake Plain see an early morning flurry, but accumulation is not expected even if it does happen. Conditions become more stable early Wednesday as the upper gradient weakens and most of the energy heads east. A few models are resolving a very positively-tilted weak trough moving through Wednesday evening, but some models show close to nothing, thus there exists only a 10-20% chance of precipitation. Thursday and potentially onwards models generally agree on a very mundane pattern as a closed high develops to our northwest and upper gradients weaken significantly. && .AVIATION...A mix of overcast VFR and MVFR/IFR in rain and snow showers. Mountain obscuration in precipitation and low clouds. Snow levels 4000-5000 ft MSL. Isolated thunderstorm development expected this afternoon mostly west and south of the Snake Plain, although a stray storm could wander into the Magic Valley. Scattered weak showers early Friday morning in the Snake Plain dissipate fully after Fri/09z. The rest of Friday will be VFR and partly cloudy. Surface Winds: W-NW 10-20 kt with gusts to 35 kt in terrain west of the Owyhee Mtns, otherwise S-SE 5-15 kt in the Snake River Valley, becoming W-NW 5-15 kts after Thu/23z. Winds aloft at 10kft MSL: W-NW 20-30 kt south of the Snake Plain, variable 5-10 kt north of the Snake Plain. KBOI...VFR with scattered/broken clouds 6000-9000 ft AGL. Weak showers in the vicinity this afternoon/evening, with a <30% chance of rain showers hitting terminal Fri/05Z-08Z. There`s a low chance (<10% chance) of a thunderstorm near the terminal Thursday afternoon, but most of the thunderstorm potential exists well south and west of the area. Surface winds: S-SE 10-20 kt, shifting to NW 5- 15 kt around Thu/23z. Weekend Outlook...Conditions become unsettled going into Sat/Sun. As the next system moves in Saturday, skies become overcast. Precipitation moves in west to east through Saturday, as mostly rain with snow levels at 6000-7000 ft MSL. Precip chances are very high Saturday, 80-100%, especially in the afternoon. The core of the colder airmass moves overhead on Sunday, dropping snow levels to ~5000 ft MSL with consistent rain/snow through the day (60-80% chance of precip area wide). Surface winds increase significantly Saturday morning and stay elevated through Sunday. SE 15-25 kt with gusts 25-35 kt Saturday afternoon, W 10-20 kt with gusts to 20-30 kt Sunday. && .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...JDS LONG TERM....JM AVIATION.....JM