textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Isolated thunderstorms across southwest Montana and Lemhi County this evening. More widespread showers and thunderstorms Saturday.

- Temperatures cooling through the weekend, running 10 degrees below normal by Sunday

The Northern Rockies remains sandwiched between a broad low pressure system over British Columbia and high pressure centered over the four corners region. The end result is southwest flow aloft over western Montana and north central Idaho. Another pulse of energy is expected to move through the flow this afternoon and evening producing isolated to scattered showers and thunderstorms across southwest Montana and Lemhi County. The main storm threats will be gusty outflow winds to 40 mph and lightning. The rest of the area will largely remain dry through this evening, though breezy southwest to west winds will develop.

Beginning tonight into Saturday, the low pressure system over Canada will stretch southwards and close off over Washington. Showers and isolated thunderstorms will develop late tonight, and become more widespread through the day Saturday. By Saturday afternoon, a cold front will move through the region, which could help strengthen a few storms, mainly along and south of Highway 12. Chances for wetting rains (more than 0.10") reaches 80 to 90 percent for west-central and southwest Montana, as well as Lemhi County. Confidence for wetting rain decreases across northwest Montana, where probabilities for wetting rains drop below 30 percent.

By Sunday, temperatures will drop into the upper 60s to low 70 for many valley locations, which is roughly 10 degrees below normal for this time of year. Breezy conditions will continue, thought higher humidities and cooler temperatures will keep the fire weather threat low.

Brief high pressure rebounds Monday and Tuesday, which will allow temperatures to warm once again into the 80s. This looks short lived however as numerous forecast models are showing the potential for a colder and potentially wetter low pressure system mid to late next week.

AVIATION

Showers and thunderstorms will again be a concern for KSMN and KBTM this afternoon and evening, mainly between 28/2200z and 29/0200z. Storms will be capable of gusty winds to about 30-35 knots and frequent lightning. The remainder of the Northern Rockies will see mostly VFR conditions with westerly or southwesterly gusts to about 20 knots in the afternoon ahead of an approaching trough of low pressure. Expect increasing clouds overnight with widespread rain starting on Saturday morning.

MSO WATCHES/WARNINGS/ADVISORIES

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