Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
499 FXUS65 KMSO 181852 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1252 PM MDT Mon Aug 18 2025 .DISCUSSION... KEY MESSAGES: - Thunderstorms capable of gusty outflow winds and brief heavy rain each afternoon/evening through Wednesday - Heat ramps up tomorrow and again this weekend The upper level pattern is expected to remain fairly stagnant over the next couple days as high pressure builds to the east and a trough of low pressure remains near the Pacific northwest. This will produce southwest flow over the Northern Rockies region, bringing warm temperatures and pulses of energy, allowing for afternoon/evening showers and thunderstorms. The main threats with thunderstorms will be lightning, gusty outflow winds near 50 mph and locally heavy rain. The stronger storms today are more likely along and south of Interstate 90. On Tuesday, that area expands northwards to include as far north as the Mission valley. On Wednesday, a dry cold front will pass through the region, associated with a disturbance moving through southern Alberta. Breezy and continued warm conditions will lead to elevated fire danger across the region. Another round of thunderstorms will also be possible, mainly focused across southwest Montana. Westerly flow aloft behind the passing front on Thursday and Friday will lead to overall drier conditions, limiting thunderstorm potential. Warm and breezy conditions will continue. By Saturday into early next week, forecast models show with high confidence (greater than 80 percent) that the ridge axis will shift westwards and build directly over the Northern Rockies region. Temperatures will ramp up, and could potentially meet heat advisory criteria, especially for the lower valleys of north central Idaho. There is also indication that monsoonal moisture may slowly progress northwards into southwest Montana and Lemhi county, bringing another period of thunderstorms to the region. && .AVIATION...Thunderstorms are anticipated to develop once again this afternoon and evening, with the threat of stronger storms most likely along and south of a line from KMLP to KMSO to KHLN. Thunderstorm threats will include lightning, gusty outflow winds (potentially up to 45 kts) and brief heavy rain. KHRF and KBTM have a 20 to 30 percent chance of seeing a storm between 18/2200z and 19/0100z. KSMN and KMSO have lower chances (10-20 percent). && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$