textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Warming and drying trend through Tuesday, with valley temperatures reaching the upper 70s to 80s.

- Rain showers and a few thunderstorms are possible Tuesday 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.

Satellite imagery this afternoon is showing a well-formed low pressure circulation off the West Coast. This system will continue east, impacting the Northern Rockies with a major shift in the weather by Wednesday. In the meantime, summer-like conditions will be the norm, as daytime high temperatures reach 20-30 degrees above normal today and on Tuesday. Tuesday will be the warmest day of the week as valley locations across the Northern Rockies reach the low to mid 80s. Record high temperatures will be in the crosshairs at Missoula, Butte, and Kalispell. Low relative humidity and strong southwesterly winds across southwest Montana will also bring concerns for near-critical fire weather.

Change arrives on Tuesday night into Wednesday. The Pacific low will make its way into the Northern Rockies, bringing a strong cold front with it. Expect daytime highs on Wednesday to be about 15-20 degrees cooler than Tuesday. The front will also bring strong westerly winds. In addition to cooler temperatures, ample moisture will accompany the low. Enough instability will be present on Wednesday afternoon to fuel isolated thunderstorms along the frontal boundary. Moderate to heavy rain will persist behind the front. Liquid precipitation totals for this event will favor the mountains of north-central Idaho and northwest Montana (70% chance of exceeding one inch, about 20-40% chance for exceeding two inches by Saturday morning). 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 on Thursday, enough for a few inches of snow to fall on Lookout, Marias, and Lolo passes by Friday morning. The southwesterly nature of this system will bring a few more inches to Homestake, MacDonald, and Lost Trail passes. If you have travel plans over the Continental Divide on Thursday into Friday, be prepared for winter driving conditions. Temperatures remain slightly below normal through the weekend.

AVIATION

Mostly clear skies and light, terrain-driven winds will result in VFR conditions into Tuesday morning.

MSO WATCHES/WARNINGS/ADVISORIES

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