textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Rises in small streams and creeks through Friday for northwest Montana, especially Lincoln and Sanders counties - Well above normal temperatures and gusty winds at times into Friday, especially I-90 southward

- More seasonable temperatures on Saturday with a cold front passage

An active moist southwesterly flow regime persists as an atmospheric river (AR) remains pinned between a Gulf of Alaska trough and a Desert Southwest ridge. The primary moisture plume continues to favor northwest Montana and the Idaho Panhandle, keeping snow levels elevated above 7000 feet. While the most intense forcing has shifted northward, light precipitation will persist through Friday morning before a secondary moisture surge brings a 30-50% probability of >0.50 inch of rainfall to Lincoln and Sanders Counties. This continued QPF, combined with high-elevation snowmelt, will maintain rises on small streams and creeks, though significant flooding is not currently anticipated.

Areas further south, generally south of Interstate 90, remain entrenched in a record-breaking warm sector. Highs will reach the upper 60s to low 70s across the Missoula and Bitterroot valleys, with mid 70s to low 80s likely for the lower Salmon and Clearwater River canyons. Record highs are specifically forecast for Butte and Salmon through Friday. This thermal profile, combined with a tightening surface pressure gradient, will support afternoon wind gusts of 25 to 35 mph. The combination of warmth, gusty winds, and low relative humidity will elevate fire weather concerns for Lemhi County and southwest Montana through the end of the week.

A pattern transition occurs Saturday as a cold front traverses the Northern Rockies, returning temperatures to seasonal averages. While this front will trigger a period of gusty winds and light, convective precipitation, overall impacts appear minimal as the deeper moisture plume exits the region.

AVIATION

An active southwesterly flow regime will maintain VFR conditions for most terminals today, though localized MVFR ceilings and visibility remain possible across northwest Montana and North-Central Idaho due to persistent light rain and low-level moisture. The primary aviation concern focuses on a tightening surface pressure gradient and deep mixing, which will generate widespread west-to-southwest surface gusts of 25 to 35 kt this afternoon, particularly for KMSO, KBTM, and KSMN. Strengthening flow aloft interacting with complex terrain will also increase the risk for mechanical turbulence and localized mountain wave activity, especially along and downwind of the Bitterroot and Sapphire ranges. While snow levels remain above 7,000 feet, obscuration of higher terrain will continue across northwest Montana through the evening.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.