textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Warm and dry today with sunny skies by this afternoon; breezy easterly winds developing into tonight.

- Shower and thunderstorms Thursday into Friday, generally south of Highway 12. Storms will be capable of brief heavy rain and small hail. - Another warming and drying trend Sunday through early next week.

Short lived high pressure over the region today will feature pleasant, sunny, and near-seasonable weather, with high temperatures reaching the 70s in western Montana and the 80s in Idaho. A pressure gradient will generate northeast winds of 10 to 20 mph during the day. Tonight, this gradient will tighten, increasing the potential for easterly wind gusts exceeding 20 to 25 mph, particularly in channeled terrain along and west of the Continental Divide.

A low-pressure system will approach southwest Idaho on Thursday, drawing a surge of abundant monsoon moisture into the area. Combined with strong wind shear, this system will trigger thunderstorms capable of producing heavy rain, lightning, gusty winds, and small hail. On Friday, potential afternoon heating could increase atmospheric instability, elevating the threat for stronger storms capable of producing larger hail. The highest probabilities for these thunderstorms will focus across central Idaho and west-central to southwest Montana, while northwest Montana will experience much lower chances for precipitation.

As the low-pressure system exits the region on Saturday, the focus for showers and thunderstorms will shift east of the US-93 corridor into central Montana, leaving the lower valleys of Idaho mostly dry with moderating temperatures. High pressure will then build across the region from Sunday into early next week. Expect patchy morning fog in river valleys followed by afternoon highs potentially reaching the 80s in Missoula and the lower valleys of Idaho. By mid-week, there is a 40 percent chance that a passing frontal system could bring breezy conditions and temper the early- week warmth.

AVIATION

VFR conditions will prevail across the western Montana and north-central Idaho airspace today under transient high pressure. A tightening pressure gradient will lead to sustained north to northeast surface winds of 10 to 15 kts by this afternoon. Tonight, this gradient will increase further bringing stronger easterly winds, reaching 15 to 20 knots through channeled terrain along and west of the Continental Divide, which will likely result in localized mechanical turbulence for general aviation. Aviation hazards will increase on Thursday as an approaching low-pressure system draws in abundant monsoon moisture. This setup, combined with strong wind shear, will trigger widespread thunderstorm activity capable of producing localized MVFR to IFR conditions in heavy rain, erratic gusty winds, small hail, and mountain obscuration. Thunderstorms will be most likely along and south of Highway 12, potentially impacting KMSO, KHRF, KBTM and KSMN.

MSO WATCHES/WARNINGS/ADVISORIES

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