textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Showers and thunderstorms today with frequent lightning, brief heavy rain, and erratic gusts.

- Elevated post-frontal winds creating choppy conditions on Flathead Lake through early Sunday.

- Unseasonably cold temperatures (10 to 15 degrees below average) bringing high- elevation valley frost Sunday and Monday mornings.

- Brief warm-up early next week followed by another cool, active trough late next week.

Today-Sunday: Numerous showers and thunderstorms have developed across north- central Idaho into northwest Montana ahead of an approaching cold front currently positioned along the Idaho/Washington border. This front will push steadily across the region through this afternoon and evening. Storms along and ahead of the boundary will be capable of brief moderate to heavy rainfall, lightning, and gusty, erratic outflow winds.

Behind the frontal passage, surface winds will become widespread and remain elevated through the overnight hours into Sunday. These gusty winds will generate choppy, hazardous boating conditions on Flathead Lake early Sunday morning before diminishing in the afternoon. Meanwhile, the main center of the low pressure system will track along the Canadian border tonight into Sunday, keeping showers and isolated thunderstorms lingering across northwest Montana.

This unseasonably cold airmass will push temperatures roughly 10 to 15 degrees below average for late August. Clearer skies and cold air drainage will allow morning low temperatures to drop into the upper 20s to low 30s across the high-elevation valleys of north-central Idaho and western Montana on both Sunday and Monday mornings, resulting in widespread frost.

Monday-Late Next Week: A transient ridge of high pressure will build over the region Monday into Tuesday, returning warm and dry conditions to the Northern Rockies. However, long-range model guidance remains in strong agreement that another significant trough of low pressure will dig into the Pacific Northwest during the latter part of next week, ushering in another stretch of cooler temperatures and active weather.

AVIATION

Showers and scattered thunderstorms will move across regional terminals this afternoon alongside an advancing cold front. Heavy downpours may cause brief localized IFR/MVFR visibilities, accompanied by erratic wind gusts. Westerly surface winds will remain elevated overnight into Sunday morning post- front, gradually easing by Sunday afternoon.

MSO WATCHES/WARNINGS/ADVISORIES

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