textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Well above normal temperatures today, with valley reaching the upper 70s to 80s.

- Rain showers and a few thunderstorms are possible this evening, bringing a risk of gusty winds, especially in north-central Idaho and NW Montana.

- Widespread rain and much colder temperatures arrive Wednesday through Friday.

A strong low pressure system is located off the West Coast. This system will continue progressing eastward, bringing a significant change in the weather to the Northern Rockies by tomorrow. In the meantime, summer-like conditions are expected today with daytime high temperatures 20 to 30 degrees above normal. Record high temperatures will be possible in Missoula, Butte, and Kalispell as temperatures climb into the upper 70s and low 80s. Dry conditions and strong southwest winds across southwest Montana will also bring concerns for elevated fire danger.

The change arrives tonight and early tomorrow morning. The Pacific storm system will make its way into the Northern Rockies, bringing a strong cold front with it. Expect daytime highs tomorrow to be about 20 to 25 degrees cooler than today. The front will also bring strong westerly winds and abundant moisture, resulting in widespread moderate to heavy rain and isolated thunderstorms. 48-hour precipitation totals ending Friday morning will favor the mountains of north-central Idaho, the Bitterroot Crest, and northwest Montana, where there is a 70 percent probability of exceeding one inch and a 20 to 40 percent of exceeding two inches. While local rivers and streams will rise, widespread flooding is unlikely at this time. Please stay alert for water pooling on roadways and the potential for small rockslides or debris flows in steep terrain.

Snow levels will drop later Thursday, lowering enough for 3 to 6 inches of snow to fall on Lookout, Lolo, and Lost Trail passes in the Bitterroot Mountains and Marias, McDonald, and Homestake passes along the Continental Divide by Friday morning. There is a 15 percent probability that up to 10 inches of snow could fall along Lost Trail and Homestake passes. If you are traveling over area passes Thursday evening and Friday morning, be prepared for winter driving conditions.

As for the valleys, if there is a period for valley snow, it will be early Friday morning. There is currently a 15 to 20 percent probability of an inch of snow, and a 50 percent for the higher valleys along the Continental Divide for the Friday morning commute.

AVIATION

Mostly clear skies and local mountain breezes will result in good flying conditions (VFR) though this morning. There is a 10 to 15 percent probability for isolated thunderstorms developing later this evening between 22/000Z and 22/0600Z for all of northwest Montana and north-central Idaho.

MSO WATCHES/WARNINGS/ADVISORIES

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