textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Widespread showers and thunderstorms Tuesday afternoon and evening, with gusty outflow winds of 30-50 mph, moderate to heavy rainfall, and lightning, strongest storms south of Highway 200.

- Another round of storms Wednesday capable of 30-50 mph outflows and heavy rain rates up to 0.5 inches per hour.

- Persistent active pattern late week into the weekend under southwesterly flow, with a 15% chance of a tropical moisture tap on Sunday.

Today through Tuesday Night: A ridge of high pressure will be over the region today, resulting in a warming and drying trend with minimal wind across the Northern Rockies. High temperatures will continue to rebound following chilly morning conditions.

Conditions shift by Tuesday afternoon as an atmospheric disturbance pushes northward out of Lemhi county and southern Idaho county into western Montana. This feature will trigger widespread showers and thunderstorms across the area. The strongest convective activity is anticipated south of Highway 200 in western Montana, where storms will be capable of producing gusty outflow winds of 30 to 50 mph, lightning, and brief moderate to heavy rainfall. Storm activity will move out of the forecast area by midnight Tuesday night.

Wednesday through Weekend: A stronger disturbance will traverse the Northern Rockies Wednesday morning through the afternoon. Storms on Wednesday will once again pose a threat for gusty outflow winds reaching 30 to 50 mph. Heavy rain potential appears enhanced with this system, with rainfall rates up to 0.5 inches per hour possible under stronger cores. Extreme southwest Montana will also be dealing with gusty winds and low afternoon humidity Wednesday afternoon and evening potentially creating critical fire weather conditions.

Southwesterly flow aloft will persist Thursday into Friday as an upper-level trough of low pressure settles over the Pacific Northwest. This setup will keep temperatures near to slightly below average for late summer, along with periodic showers and thunderstorms, particularly during pressure trough over the region through the weekend. Roughly 15% of ensemble guidance indicates the potential for a tap of significant tropical moisture on Sunday. Regardless of weather this moisture plume materializes, the Northern Rockies will remain embedded in an active, unsettled weather pattern through the weekend.

AVIATION

High pressure will continue to bring VFR conditions and light, diurnally driven winds today. Convection returns Tuesday afternoon, as showers and thunderstorms develop across central Idaho by early afternoon, spreading northeastward into western Montana through the early evening. Gusty outflow winds and lightning will be the primary storm threats, with probabilities for outflow winds in excess of 35 mph reaching 50-70% percent along and south of Highway 200.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Fire Weather Watch from Wednesday afternoon through Wednesday evening for East Beaverhead.

ID...None.