Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
724 FXUS65 KBOI 010957 AFDBOI Area Forecast Discussion National Weather Service Boise ID 357 AM MDT Wed May 1 2024 .SHORT TERM...Today through Friday night...A well defined mid- level circulation over e-central Oregon is tracking southeastward along the I-84 corridor. This feature and accompanying cold air aloft will be the focus of shower development today as it tracks through w-central Idaho. Daytime instability and dynamics will support vigorous showers and a slight chance (15%) of thunderstorms across e-central and the w-central ID mtns. While showers will be concentrated over higher terrain, some spillover is possible in the Snake Plain, especially areas near the foothills. Snow levels will be 3500-4500 feet so heavier showers/thundersnow could reduce visibilty. Today will have the feel of an early spring day as highs top out around 10 degrees below normal and gusty northwest winds bring a wind chill. Gusts up to 25 mph are possible for most, with stronger gusts to 35 mph expected across s-central Idaho. There is little rest before the next trough arrives Wednesday night into Thursday with another round of precipitation. This system will track through SE Oregon bringing widespread rain/snow showers to the mountains (50-80%) with lower probability for measureable rain in the Snake Plain (20-30%). Snow levels will start between 3500-4500 feet Thursday morning, rising to 4500-6000 feet in the afternoon. By Thursday night the wave is exiting into eastern Idaho allowing for drier conditions to develop. A short wave ridge transits the Intermountain NW Friday bringing dry and seasonable conditions. Friday night will see clouds and precipitation chances increase across SE Oregon as a deep closed low approaches the Pac NW coast. Today is the coolest day with temperatures around 10 degrees below normal. Thursday is slightly warmer, before reaching normal on Friday. .LONG TERM...Saturday through Wednesday...An upper level low will deepen off the PacNW coast on Saturday, bringing warm southwest flow to the region ahead of cooler and unsettled conditions through much of the long term period. Model agreement remains quite high during the early part of the weekend, with the deterministic storm tracks aligning more with the ECMWF AI 00Z run, pushing the low center further into our region. Therefore, confidence is increasing in a potentially impactful winter weather event for the region, especially over higher terrain. Temperatures will be highest on Saturday, with the best chance for precipitation (60-70% chance) in southeast Oregon on Saturday ahead of the colder and wetter air mass that will move in to the region on Sunday. This low will have record low 500 mb heights, so record cold temperatures are likely along with low elevation snow Sunday morning. Snow levels will be around 5000-6000 feet on Saturday, dropping to 4000-5000 feet by Sunday during the day. However, there is a potential for snow levels to drop to valley floors overnight on Sunday, it will just depend on how models continue to resolve this record cold system as we get closer to the weekend. This system also looks quite moist, with precipitable water values near the 90th percentile. Heavy mountain snow accumulations are likely, with the potential for snow accumulations in the valleys as well. Current models show high confidence (60-70% chance) of more than 8 inches of snow above 7000 feet from Saturday to Monday. Model blends show about a 20-30% chance of at least a tenth of an inch of snowfall in the Treasure Valley by Sunday morning. Daytime highs will warm quite a bit due to the higher sun angle this time of year, so any snowfall below 5000 feet will likely melt later in the day. The low will then dig and deepen into the Great Plains by Monday, but cold and moist northwest flow will continue keeping snow levels around 5000-6000 feet through the early part of next week, with widespread precipitation likely each day through Wednesday. There is some disagreement towards the end of the period, with the potential for a ridge to build in by Wednesday night, but cluster and ensembles show quite a bit of range, leading to low forecast confidence by the end of the long term period. && .AVIATION...Mainly VFR. Isolated to scattered rain/snow showers over Baker County and the West Central/Boise Mountains. Snow showers obscuring mountains and producing brief MVFR conditions. Snow levels around 3500-4500 ft MSL. Surface winds: W-NW 5-15 kt, with gusts to 30 kt through Thurs/03z near KTWF/KJER, becoming variable less than 10 kt overnight. Winds aloft at 10kft MSL: W-NW 15-25 kt. KBOI...VFR with scattered/broken low to mid-level clouds this morning. Isolated showers will pass north of terminal through the morning. Snow levels as low as 3500 ft MSL today. Generally NW 8-12 kt with gusts to around 20 kt through the afternoon, becoming variable less than 5 kt overnight. && .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...DG LONG TERM....SA AVIATION.....SA