textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Mild daytime temperatures through Thursday.

- Patchy valley fog around sunrise each morning.

- Significant weather change coming Friday into the weekend.

A broad ridge of high pressure will continue to bring mild daytime temperatures across the Northern Rockies through Thursday. Stable conditions under the ridge are promoting the development of daily valley inversions and trapped cold air, with patchy dense fog. Afternoon temperatures will continue to run 10 to 15 degrees above normal for this time of year. Forecast models suggest a few isolated showers developing over Lemhi County this afternoon, then over southwest and west-central Montana tomorrow afternoon and evening.

Expect a significant change as a low pressure system and cold front track across the region Thursday night into Friday. The front will bring wind gusts around 20 mph in Idaho and 20 to 35 mph across most of western Montana on Friday. Moisture with this system will move north from the Great Basin, with precipitation focusing along and south of the I-90 corridor and along the Continental Divide in northwest Montana. Most of the precipitation will fall as rain ahead of the cold front, limiting the potential for winter weather impacts. Snow levels will fall to around 5,000 feet Friday and lower over the weekend as shower activity begins to decrease. Therefore, forecast snow amounts will be generally under an inch across the region and above 5,000 feet. The exception is the higher elevations of the Flathead National Forest and Glacier National Park, which will likely pick up several inches of snow this weekend.

There remains considerable uncertainty in the extended forecast as the majority of long-range forecast models have different opinions on the overall pattern early next week. Twenty percent of the models show another ridge of high pressure returning to the region, with the other models suggesting a southwest flow or a cold Canadian trough. Stay tuned.

AVIATION

Stable conditions will continue today under a ridge of high pressure. Valley inversions and cold air pools will set the stage for areas of valley fog, particularly near large bodies of water and river systems. The primary period to watch will be from 21/1200-1500Z, including Terminal KMSO. Fog can not be ruled out at KGPI as well, but the probability of impacts is less than 10 percent as high cloud cover has reduced overnight cooling.

MSO WATCHES/WARNINGS/ADVISORIES

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