textproduct: Missoula

DISCUSSION

KEY MESSAGES:

* Strong, sudden northeast wind shift this evening across northwest Montana, including Flathead Lake.

* Thunderstorms capable of 50+ mph wind gusts across southwest Montana and extreme northwest Montana, late-afternoon and evening.

Fire Weather, Air Quality, and Northeast Wind Today/Tonight:

Smoke has once again pooled into valley areas this morning as sharp inversions have developed overnight under clear skies. GOES Satellite imagery shows monsoon moisture beginning to stream into mid-upper levels of the atmosphere as south-southwest flow has developed aloft. Warm and dry conditions are expected in lower portions of the atmosphere through this afternoon, with late afternoon gusty winds leading to elevated fire weather concerns, especially across southwest Montana. The afternoon winds may provide localized temporary relief from highly concentrated wildfire smoke. Confidence has increased for a strong and sudden northeast wind shift this evening across northwest Montana, with gusts of 30-40 mph across the Flathead Valley, Flathead Lake, and western foothills of the Mission Mountains. A lake wind advisory has been issued as this wind shift will bring hazardous conditions for those with plans on outdoor lakes this evening.

Thunderstorms Return:

Monsoon moisture will continue to stream into the region, opening the door for high based showers and thunderstorms by mid-afternoon through the evening. Warm and dry sub-cloud layers will promote mainly dry thunderstorms capable of 40+ mph wind gusts over southwest Montana and across extreme northwest Montana. Little appreciable rainfall is expected with the Wednesday storms, however moisture will become much more available for subsequent days through the weekend. In fact, a marginal risk of excessive rainfall arrives as soon as Thursday, with recent and ongoing wildfires having the highest risk of runoff and flood impacts. The presence of wildfire smoke will be a bit of wild card in the efficiency of thunderstorm development.

Bigger pattern change to come?

Long range model ensembles suggest that a low pressure trough will persist off coastal western US next week. Most pattern solutions feature either southwest flow aloft or a ridge of high pressure over the Northern Rockies. Either way, the moisture from tropical storms in the Pacific Ocean will play a factor in whether temperatures return to summertime warmth or not. Wildfire smoke is still a big question mark next week. Overall, the pattern will be moving away from elevated to critical fire weather concerns (hot, dry, windy pattern) that we've had consistently for many days.

AVIATION

Wildfire smoke will continue to limit visibility across the Northern Rockies air space during the next 24 hours. These visibility reductions will be focused during the morning hours, from Missoula into the Bitterroot Valley and along the divide in Southwest Montana. Shower and thunderstorm activity will develop across the higher terrain in Lemhi County into Southwest Montana and far northwest Montana by early afternoon. Lightning chances increase (30% probability) for KGPI and KBTM after 12/2100Z as well. Another weather impact during this time will be surface wind shifting to northeast from north to south across western Montana this evening into Thursday morning. 30-40 knot winds will exist over the terrain along the portion of the Continental Divide just east of KGPI, with lesser wind speeds further south.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Lake Wind Advisory from 6 PM this evening to midnight MDT tonight for Flathead/Mission Valleys.

ID...None.