Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
447 FXUS65 KBOI 040240 AFDBOI Area Forecast Discussion National Weather Service Boise ID 840 PM MDT Wed Jul 3 2024 .DISCUSSION...Breezynorthwesterly winds will persist through this evening, with gusts up to 40 MPH, especially in the Western Snake River Plain until sunset. A few small fires (less than a tenth of an acre) have been detected this afternoon, but they are not producing significant smoke at this time. Winds are expected to lighten on the 4th of July, with gusts up to 25 MPH possible from Mountain Home through the Western Magic Valley. Temperatures tomorrow will be near normal. Starting on Saturday, a heat wave will begin across the Intermountain West, with temperatures expected to exceed 100 degrees by Sunday and potentially continue through next Wednesday. Confidence is high for a series of hot days, though the maximum temperature predictions vary significantly among ensemble members. Currently, the NBM and GFS models are on the higher end of temperature guidance, with the deterministic GFS being the highest, in some cases by over 5 degrees. There is considerable uncertainty in the guidance regarding the return of monsoonal moisture for the middle of next week, which is typical for this setup potentially affecting max temperatures. The projected model pattern aligns with similar past heat waves, notably in 1960, 2015, 2018, and 2022. An excessive heat watch has been issued for this event. No updates are needed at this time. && .AVIATION...VFR. High density altitude by the weekend and next week. Surface winds: variable 10 kt or less overnight, then N to NW 5-15 kt with gusts to 15-20 kt Thursday afternoon. Winds aloft at 10kft MSL: W-NW 10-20 kt. KBOI...VFR. Clear. Surface winds: variable or southeast up to 6 kt overnight, returning to NW 5-15 kt after Thu/18Z. High density altitude by the weekend and next week. && .PREV DISCUSSION... SHORT TERM...Tonight through Friday night...A Red Flag Warning is still out for parts of Southern Idaho, with at least one RAWS site reporting critical RH and wind so far. Temperatures warming through the short term. Near normal on Thursday increasing to 5 degrees above normal on Friday. Winds after Wednesday afternoon should become fairly typical. With the exception that gusts to 20-25 mph are possible Thursday afternoon between Mtn Home, Twin Falls, and Fairfield. In the same area, gusts to 25-35 mph are possible Friday afternoon. This could be a concerning fire weather set up with continued dry conditions, but not necessarily critical based on the current forecast. LONG TERM...Saturday through Wednesday...Still high confidence in the development of a heat wave that will commence this weekend and persist into next week. An intense high pressure system near the west coast gradually moves eastward and the axis reaches our area by Monday. This will prolong and intensify our current very dry conditions, but the main hazard is the heat. Temperatures warm to near or over 100 degrees on Saturday and continue to gradually increase through the long term. By Tuesday our area warms to about 10-15 degrees above normal, which means highs in the range of 105-110 for our lower Snake Plain zones. This level of heat is flagged as mostly Major with some areas of extreme through our Heat-Risk product, meaning most people should take care to prepare for the heat, especially those sensitive to heat. The longevity of the heat is another major factor, with no definite end to heat in the forecast. Latest forecasts are challenging a few records, one of which is the most consecutive days of 105 or greater in Boise. The current record is 4 set in 2002, and the extended NBM indicates we could begin recording consecutive 105 days after Tuesday through the rest of next week. There will be some relief overnight as the lows stay around 70 in the Snake Plain and lows 60s to upper 50s for mountain valleys. Either way, the afternoon heat will be extreme. As a result, we are issuing an Excessive Heat Watch for most low elevation zones. The Watch for SE Oregon and the Lower Treasure Valley go into effect this Weekend, while the Watch for the rest of the Snake Plain/TV, far SW Idaho, and the Weiser Basin goes into effect on Monday. High elevation zones are very close to needing a product, but confidence isn`t quite high enough and the heat in these zones is still many days away. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Excessive Heat Watch from Saturday afternoon through Wednesday afternoon IDZ012-029. Red Flag Warning until 9 PM MDT this evening IDZ424-426. Excessive Heat Watch from Monday afternoon through Wednesday afternoon IDZ014>016-030-033. OR...Excessive Heat Watch from Saturday afternoon through Wednesday afternoon ORZ061>064. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...JDS AVIATION.....SH SHORT TERM...JM LONG TERM....JM