textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A warming trend continues through the weekend with isolated storms in Northwest Montana this afternoon and evening.

- Showers and thunderstorms chances increase region-wide by late Monday.

- A large, slow-moving weather system will bring widespread rain and cooler temperatures Tuesday through much of next week, with a 50 to 70 percent chance of at least a quarter inch of rain by Wednesday morning.

Scattered showers will develop this afternoon and evening, primarily across northwest Montana and along the Continental Divide. Impacts will stay largely limited to brief rain showers and localized wind gusts up to 30 mph. There is enough atmospheric energy to support an isolated thunderstorm over Glacier National Park. By tonight, showers will diminish as a ridge of high pressure builds into the Northern Rockies. This ridge will provide a dry, sunny weekend with temperatures climbing 10 to 15 degrees above normal for late May.

A major pattern shift begins on Monday as a large area of low pressure drops into the Pacific Northwest. This will switch our winds to the southwest, drawing moisture and instability into the region. Widespread showers and thunderstorms will develop by Monday afternoon. Storms on Monday could produce gusty winds, frequent lightning, and small hail.

By Monday night, a cold front will cross western Montana and north-central Idaho. As the front pushes east, wrap-around moisture will fill into the region. Tuesday is currently forecast to be the wettest and coolest day of the week, with high temperatures struggling to reach the 50s and 60s.

Heading into Wednesday and Thursday, the low-pressure system is most likely to stall to our south over the Great Basin. This setup will pull unusually high levels of moisture northward from the Plains into Montana. Forecast models suggest atmospheric moisture will reach 150 percent of normal for late May. This moisture connection will introduce the threat of heavy rainfall and embedded thunderstorms Thursday and Friday.

AVIATION

A dry and stable airmass will maintain VFR conditions across the Northern Rockies airspace through the weekend, with one minor exception this afternoon. Sufficient instability near Glacier National Park may trigger an isolated thunderstorm or robust shower between 21Z and 03Z. This activity could result in localized MVFR conditions and erratic wind gusts up to 25 knots impacting the KGPI terminal. Otherwise, anticipate light, terrain- driven diurnal winds at KMSO, KBTM, KSMN, and KHRF through Sunday.

MSO WATCHES/WARNINGS/ADVISORIES

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