textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Warming trend Friday into the weekend, with moderate heat risk impacts across low elevations of central Idaho.

- Next system arrives Monday into Tuesday, with potential for backdoor cold front, northeast winds, and recreation impacts. GOES Satellite and radar observations this afternoon show a upper level disturbance moving across southern Alberta, with scattered showers across northern portions of Lincoln and Flathead Counties. Blustery westerly winds have began to surface, with gusts expected to reach 25-30 mph across valley areas through this evening across western Montana. Higher gusts near 40 mph have been observed across high elevations along the divide in northwest Montana, including Logan Pass in Glacier Park. Showers will continue through this evening across northwest Montana, focusing across Glacier Park, with enough moisture and instability being present for a couple isolated thunderstorms.

A ridge of high pressure will amplify along the Pacific Northwest coast Friday into the weekend. This will place the Northern Rockies under a warm and dry west-northwest flow pattern. Confidence is high for rising temperatures through the weekend, with highs reaching into the upper-90s to low-100s across lower elevations of central Idaho. These temperatures will stretch over the weekend, leading to a moderate risk of heat impacts. Temperatures will also run 10-15F above normal across western Montana, with Sunday being the warmest day of the upcoming week.

Ensemble models continue to suggest a breakdown of the ridge Monday into Tuesday next week as a trough drops southeastward from British Columbia. Half of ensemble clusters bring a strong backdoor cold front southward from Canada across the divide Monday evening into Tuesday morning, with north-northeast winds developing across western Montana. Guidance has trended towards this solution, with previous ensemble runs showing a 20% chance for this solution 12-24 hrs ago. Precipitation will generally focus along the divide in northwest Montana under this scenario, with probabilities for >0.10" of precipitation peaking at 50-60% across Flathead County and the divide. The bottom line is those with plans across the higher elevations and in Glacier Park should monitor the forecast closely given the potential for widespread precipitation, much colder temperatures, and north- northeast winds making for adverse backcountry conditions for this time of year. Furthermore, choppy lake conditions across Flathead Lake would be a concern if this backdoor cold front solution comes to fruition. We will monitor this system closely in the coming days.

AVIATION

GOES Satellite imagery shows a cumulus field along and north of the I-90 corridor associated with a passing disturbance along the US-Canadian border. Scattered showers are seen on regional radar imagery across Lincoln and Flathead County as of 10/1900Z. This activity will continue into the evening, with the risk of lightning from isolated thunderstorms focusing east of KGPI over Glacier National Park and the divide. Blustery westerly winds of 20-25kts will continue through 11/0200-0400Z for valley areas as this disturbance passes. Skies will clear overnight as high pressure begins to build into the region.

MSO WATCHES/WARNINGS/ADVISORIES

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