Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
035 FXUS65 KBOI 200244 AFDBOI Area Forecast Discussion National Weather Service Boise ID 844 PM MDT Tue Aug 19 2025 .DISCUSSION...A weak shortwave passing through this evening generated cumulus development over the higher terrain along with a few thunderstorms across Valley, Adams, and Baker Counties. As of 8:30 PM MDT, only one storm remains, located about 8 miles east of Council. Storm activity will continue to diminish overnight as surface instability weakens with the loss of daytime heating. Smoke from the Cottonwood Peak Fire in Elko County, Nevada has expanded northward, spreading through the Treasure Valley and reaching as far as Stanley. The Box Fire in far western Owyhee County has also become more active, adding to the hazy and smoky conditions. Smoke layers are expected to remain aloft through tonight into Wednesday morning. A weak frontal passage on Wednesday will bring increased southwesterly flow, helping to shift smoke farther east. && .AVIATION...VFR. Mostly clear skies. Few stray showers/thunderstorms over W-Central ID Mtns (near KMYL) this evening. Local visibility reductions in the W-Central ID Mountains and Snake Plain near Mtn Home due to wildfire smoke. Surface winds: variable under 7 kt or NW 7-12 kts. Winds aloft at 10kft MSL: S-SW 20-30 kt. KBOI...VFR. Smoke layers aloft. Surface winds: NW 10-15 kt becoming light and variable later this evening and overnight. && .PREV DISCUSSION... SHORT TERM...Tonight through Thursday night...An upper-level ridge is building into the four corners region, and will continue to develop over the next few days. Along with this, an upper-level trough will be moving east along the southern Canadian provinces, and combined, this pattern will lead to southwesterly flow aloft. Weak shortwave troughing will move across our northern zones Wednesday, which will keep temperatures only near 5 degrees above normal. Hot, dry, and breezy conditions will dominate through the period. Smoke from nearby wildfires will continue to move into the region. Small chance (<10%) of precipitaiton near the Western Magic Valley on Wednesday and Thursday. LONG TERM...Friday through Tuesday...Ridge, monsoonal moisture, and thunderstorms...a combo for an active long term. An upper-level ridge over the four corners region will drift ever-so-slightly west, causing southerly flow aloft. This creates a myriad of effects, the most prevalent of which will be heat. Daily highs Fri-Mon will be 5- 15 degrees above normal, with Saturday looking to be the warmest, as well as have the least cooling relief overnight (Sat into Sun). Along with the heat, moisture will begin to stream in steadily with southerly flow aloft. PWAT values frosouth ofm the LREF has a vast increase of mid-level moisture occurring on Friday and Saturday, and lingering through the extended. The ensembles are currently showing values greater than 0.70" areawide Sunday, with lower elevation maxima getting over 0.90" PWAT at times. This would be very high PWATs for this time of year, with the 75th percentile being 0.68", and the 90th percentile being 0.82". What do all of these numbers mean? Well, afternoon precipitation chances rise from 15-20% Saturday over primarily the Southern Highlands to near 20%-50% Sunday, Monday, and Tuesday. Thunderstorm chances also look high during this period, but there is too much uncertainty this far out with spatial coverage. Precipitation combined with high PWATs could lead to an elevated risk for localized flooding effects, especially Sunday-Tuesday. Otherwise, with the very warm and dry surface conditions, high bases should make winds the primary threat, but also hint at a risk of dry thunderstorms. Fire weather risk will be elevated coming out of the warm and dry midweek into the dry thunderstorm potential late this weekend. Smoke is expected to continue from local fires. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise DISCUSSION...JDS AVIATION.....JY SHORT TERM...CH LONG TERM....CH