Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
270 FXUS65 KBOI 030239 AFDBOI Area Forecast Discussion National Weather Service Boise ID 839 PM MDT Sun Jun 2 2024 .DISCUSSION...Showers are progressing east across the area as expected this evening, and will intensify overnight. No consistent trend is evident in the latest model QPF, so no changes will be made this evening. Please see the Flood Watch that was issued earlier today, and the detailed previous discussion, for additional information. && .AVIATION...Rain through late Monday morning at all sites except KJER/KTWF, where rain chances increase after 03/12Z. Widespread MVFR/IFR likely at KBKE/KMYL. Periods of MVFR possible (40-60% chance) elsewhere. Mountains obscured in rain and clouds. Areas of LLWS through 03/15Z. Surface winds: SW-NW 10-20 kt, except SE 5-15 kt becoming W-W after 03/16Z in the Treasure Valley. 10k ft MSL winds: W 35-50 kt. KBOI...VFR with periods of MVFR. Rain beginning 03/04-03/06Z and persisting through late Monday morning. Medium confidence (60% chance) of MVFR ceilings below 3 kft between 13Z-17Z. Rain ends Monday afternoon with westerly gusts increasing to around 20 kt. && .PREV DISCUSSION... SHORT TERM...Tonight through Tuesday night...A strong surge of moisture will flow into our area this evening. It is still forecast to qualify as a moderate atmospheric river. While lots of the moisture will struggle to make it over the Cascades, we are still forecasting near record amounts of PW in our area and QPF for the Mountains. PWs of just under an inch throughout the event and orographic effect support rainfall amounts of near to just under an inch in mountain valleys, and 2-3 inches on mountain ridges. There will be some terrain shadowing, especially NE of the Steens and the Owyhees, but valley locations near the foothills will see amounts of 0.2-0.6 inches, strongly correlated to proximity to the terrain. Shadowed regions and portions of far SE Oregon will still see some rain, but closer to 0.05 inches. As mentioned in the morning discussion QPFs did come down a hair with this latest forecast, especially as early observations from the coast are on the lower end of the forecasted range, but storm total amounts didn`t actually change that much even taking these into account. While the trend of underachieving could continue leading to a wide range of outcomes, the current forecast is still the most likely scenario. Steady rainfall will last from about Sunday evening to Monday evening, though most Oregon locations will end closer to noon on Monday. Monday afternoon and evening, in the mountains, some low-level instability will aid in the development of banded terrain driven storms and heavier showers. High resolution models are consistently resolving these types of training showers in portions of the West Central Mountains. These storms will cause locally much higher rainfall as they train over the same areas downstream of terrain. The current QPFs, banded storms, and snowmelt augmentation has warranted the issuance of a Flood Watch. The timing of the Flood Watch is offset from the beginning and ending of rain as it may take a few hours for water to travel to areas of elevated flood potential. Mud or rockslides are also possible in the watch area, especially under banded storms. Monday afternoon will also be breezy for SE Oregon, far SW Idaho, and the Magic Valley. Gusts of 35-45 mph are possible with sustained winds near 20-25 mph. Some clearing Tuesday morning could allow for fog and low stratus clouds to form in valleys, especially in areas with poor drainage where standing water and saturated surface soils will contribute to fog development. As the low pressure and moisture move east, temperatures increase on Tuesday as high pressure builds and a sharp warming trend begins. LONG TERM...Wednesday through Sunday...Models remain consistent in showing an upper ridge over the southern U.S. expanding northward and persisting into next weekend. The expansion of the ridge results in unseasonably hot temperatures developing by Thursday and lasting into the weekend. There remains a high probability (60-90 percent chance) of high temperatures exceeding 90F in the lower valleys (including the Treasure Valley) and about a 30 percent chance the Ontario area in the Lower Treasure Valley could reach 100F (which would be near record territory). Models also remain consistent in showing enough moisture available for a chance (20-30 percent) of showers and afternoon/evening thunderstorms each day beginning Thursday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Flood Watch from midnight MDT tonight through Monday evening IDZ011-013. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...SP AVIATION.....JR SHORT TERM...JM LONG TERM....TL