textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Widespread showers and thunderstorms today with outflow gusts of 25-45 mph and heavy rain rates up to 0.5 inch per hour

An upper level disturbance and associated cold front tracking across the Northern Rockies has already initiated showers and thunderstorms over north-central Idaho this morning, and will progress northeastward across the Continental Divide by mid- afternoon (3-4pm MDT). Primary hazards include brief heavy rainfall and erratic outflow gusts of 30-50 mph, with a 5 to 10 percent probability of severe gusts in northwest Montana and along the Divide. Recent high resolution models also show stronger cells capable of hail and near severe winds from Lemhi County northeast through Silver Bow County, most likely between 1pm and 3pm MDT.

While winds will generally subside following the frontal passage, elevated gradient winds will persist through sunset across Lemhi County and southwest Montana. Post-frontal showers will develop this afternoon and continue into Thursday, yielding a 60 to 80 percent probability of wetting rain (0.10 inches or greater) across the majority of western Montana and north central Idaho.

The notable exception to this precipitation is far southwest Montana, where gusty winds and low relative humidity will drive critical fire weather conditions from this afternoon through Thursday afternoon. Elevated fire weather conditions will linger into Friday due to the slow frontal progression.

Looking ahead, persistent southwesterly flow aloft will dominate Thursday into Friday as a broad upper trough settles over the Pacific Northwest. This pattern supports near to slightly below normal temperatures alongside daily scattered afternoon and evening convection. North-central Idaho is favored for heavier accumulations during this timeframe, with high probabilities (60 to 80 percent) of exceeding 0.50 inches.

Ensemble guidance indicates general troughing will persist through the weekend before a more pronounced shortwave ejects across the region on Monday. Approximately 50 percent of ensemble solutions depict a closed low tapping into deeper tropical moisture, which aligns with current NBM probabilities of 50 to 70 percent for widespread precipitation exceeding 0.25 inches to start the next work week across a large swath of the Northern Rockies.

AVIATION

Aviation interests across western Montana and north central Idaho will experience widespread impacts today as an upper-level disturbance and cold front sweep through the region. Showers and thunderstorms initiating over north-central Idaho this morning will track northeastward across the Continental Divide by 21Z-22Z (3-4 PM MDT), producing localized MVFR to IFR conditions in brief heavy rain, mountain obscurations, and erratic outflow wind gusts of 25 to 45 kts. Recent high-resolution guidance highlights a corridor from Lemhi County (KSMN) northeastward through Silver Bow County (KBTM) for stronger convective cells capable of hail and near-severe gusts between 19Z and 21Z (1-3 PM MDT). Following the frontal passage, elevated gradient winds will persist across Lemhi County and southwest Montana until sunset, while widespread post frontal showers fill in across the broader region and continue into Thursday, maintaining periods of reduced flight categories.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Red Flag Warning until 8 PM MDT Thursday for East Beaverhead.

ID...None.