Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
349 FXUS65 KMSO 161832 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1232 PM MDT Sat Aug 16 2025 .DISCUSSION... KEY MESSAGES: - Thunderstorms capable of gusty outflow winds and brief heavy rain this weekend. - Above normal temperatures, with typical hot, dry, summer pattern by mid next week. GOES Water Vapor imagery early this afternoon shows moisture streaming from the Pacific ocean off the northern California coast through the ID/MT border. Widespread cloud cover and shower activity has been observed within this moisture fetch, where precipitable water values are near 200% of normal. This area of shower activity will shift eastward into central Idaho and northwest Montana through this evening; however, widespread wetting rains are not expected as moisture is currently focused in the mid-upper levels of the atmosphere. Further east, mostly sunny skies will allow for the atmosphere to destabilize, with high resolution models developing convection between 200-400PM across Lemhi County, ID and southwest Montana (generally south and east of Missoula). Outflow winds are the main concern, with stronger cells capable of producing gusts near 50 mph. Thunderstorms will also produce brief heavy rain under the stronger cores, with a 10% chance for excessive rainfall leading to localized flooding to burns scars and flood prone areas across Ravalli, Granite, and Powell Counties. Models have been consistent with highlighting nocturnal showers and isolated thunderstorms tonight. Activity will develop late this evening across northeast OR as an upper level wave moves into the region within southwest flow. This overnight development will generally focus across north-central Idaho into west-central Montana. By Sunday, showers and thunderstorms will focus across southwest Montana, generally along and south of I-90. Forecast soundings suggest deeper instability will be present, with CAPE climbing near 750-1000 J/kg by the afternoon. Forecast models suggest higher probabilities for thunderstorms, with 4-hr chances for lightning peaking at 70-80% along the divide from 300-600 PM MDT. Storms will once again be capable of outflow winds and localized heavy rainfall. Flood prone areas will be monitored for an outside chance for flash flooding. Looking ahead to early next week, the region will remain under the influence of southwesterly flow, as high pressure strengthens over the Four Corners region. Pacific moisture will fuel high- based convection Monday into Tuesday, with lesser coverage compared to this weekend. By Wednesday into Friday, a familiar mid-August pattern will be in place, with hot and dry conditions. && .AVIATION...Regional radar imagery shows a line of showers moving through eastern Washington and the Idaho Panhandle early this afternoon. Showers will continue eastward into northwest Montana and Idaho/Clearwater Counties through this evening, with limited visibility impacts given the elevated nature of activity. Further east, thunderstorms will develop between 16/2000-2200Z south and east of the I-90 corridor. Thunderstorms will develop in the vicinity of KSMN, KHRF, and KBTM through this evening, with outflow winds and brief heavy rain being the primary threats. The highest probabilities for outflow winds greater than 35 mph will focus along the divide, near KBTM, reaching 70% from 300-600PM. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...&& $$