textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Decreasing smoke this afternoon and tonight

- Thunderstorms this afternoon/evening featuring gusty outflow winds

- Pattern change to cooler and wetter weather early next week

Satellite imagery early this morning indicates a well-formed low pressure circulation off the coast of the Pacific Northwest. While it spins off the coast, a ridge of high pressure will move east of the Northern Rockies today. This scenario will put the Northern Rockies under southwesterly flow aloft. The low will send Pacific moisture into the region, fueling the potential for thunderstorms this afternoon and evening. Expect scattered showers and thunderstorms to initiate early/mid afternoon and press northeastward impacting much of the area, mostly concentrated from Flathead Lake southward. Greater instability and wind shear will allow for the potential of a few strong storms with gusty outflow winds and small hail being the main concerns. High resolution model output is indicating gust potential of 35 to 45 mph this evening. A direct hit on a burn scar could also lead to a localized debris flow. Smoke once again may be a limiting factor to thunderstorm coverage and intensity, although smoke dispersion models show smoke gradually diminishing in intensity throughout the day today.

On Monday, the Pacific low will make landfall in the Pacific Northwest and send a good fetch of Pacific moisture into the Northern Rockies from the south. This system will initiate a cooler, wetter pattern starting on Tuesday and lasting into next weekend. Daytime temperatures return to seasonable levels with low/mid 70s in western Montana valleys, mid 70s to low 80s for north-central Idaho valleys. Showers and a few thunderstorms will be common each day with hints of a closed low sliding south of the region later in the week. If this closed low does develop, then widespread precipitation would be the outcome. Still a lot of details to be ironed out but certainly a cooler and wetter pattern ahead.

AVIATION

A weak shortwave trough embedded in southwesterly flow aloft will keep some chances for showers in the forecast for early this morning. Smoke will cause reductions in visibility through early this afternoon south of about I-90, and through this evening north of I-90. This afternoon, increasing instability will accompany moisture from the southwest, creating a favorable environment for thunderstorms. Guidance is indicating chances for outflow wind gusts of 30 to 40 knots. Thunderstorm coverage will be throughout the Northern Rockies airspace south of about Flathead Lake. The wildcard will be lingering smoke if smoke can persist longer than predicted into this evening, it will inhibit initiation of convection.

MSO WATCHES/WARNINGS/ADVISORIES

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