textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Near record cold temperatures forecast for Sunday morning

- Slow warming trend with lingering showers, especially during the afternoon and evening

The cold air that has settled over the Northern Rockies will allow temperatures to drop near to well below freezing in many locations across the region tonight putting flowering plants and above ground plumbing in danger of damage, so a frost advisory and freeze warnings remain in place.

The Northern Rockies will remain under northerly to northwesterly flow this weekend into mid next week. This flow pattern will allow for a very gradual warming trend with temperatures finally reaching near normal seasonal readings by Wednesday. The flow pattern is also conducive to lingering light showers, especially across western Montana. The shower activity will pick up in coverage and intensity during the afternoon hours and then diminish after sunset each day. A few subtle features are expected to pass through the region under this flow pattern which appears to keep the shower activity to linger slightly longer, especially along the Continental Divide around Glacier National Park. These showers could create isolated snow covered roads during the overnight hours and into the early morning hours.

The long term guidance is showing a weak ridge of high pressure moving over the region by the latter part of the work week. This ridge appears to cause temperatures to climb to around 10 degrees above normal along with drier conditions. This ridge appears to be short lived as another disturbance is expected to impact the western United States by the weekend.

AVIATION

Shallow moisture and instability has allowed for scattered showers across the Northern Rockies this afternoon, with activity focused along and north of the I-90 corridor. Shower activity has largely developed across the higher terrain, where brief periods of IFR/MVFR visibility can be expected from rain/snow showers. These showers will be convective in nature, with turbulence near convective cores. High-resolution models suggest shower activity will develop near KBTM this evening, with a 30% chance for brief visibility reductions to 3SM after 26/0200Z. Overnight, a tightening pressure gradient will drive east-northeasterly winds through terrain-channeled valleys, introducing areas of turbulence and localized crosswinds at impacted terminals. Furthermore, stratus clouds will expand, with 3,000-5,000 feet ceilings across western MT, with the lowest ceilings along the divide.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Freeze Warning until 8 AM MDT Sunday for Bitterroot/Sapphire Mountains...Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region...Missoula/Bitterroot Valleys.

ID...Freeze Warning until 8 AM MDT /7 AM PDT/ Sunday for Eastern Lemhi County...Northern Clearwater Mountains...Southern Clearwater Mountains.

Frost Advisory until 8 AM MDT /7 AM PDT/ Sunday for Orofino/Grangeville Region...Western Lemhi County.