textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Active, wet pattern continues through this week.

- Snow levels fall down to valley floors Monday causing snow showers through the end of the week.

- Long range models agree well on a return to a ridge pattern next weekend.

The active, wet pattern continues through most of this week, though a series of Pacific cold fronts are bringing the snow levels down. By Monday night, models have the snow levels affecting the valleys of central Idaho and all of western Montana, but especially northwest Montana. Current forecasts show mainly nuisance impacts in the valleys with several inches of snow in the mountains.

Right now the most significant snows are expected Tuesday afternoon through Wednesday morning. High end forecasts (90th percentile) have around 6 inches of snow at Marias and Lolo Passes with over a foot of snow in 24 hours at Lookout Pass. Those are the hardest hit passes in our region. Most valley locations have an inch or less in 24 hours, even in the high end forecasts with the exception of northwest Montana including Troy, Libby, and especially the Yaak area where models are showing 4 to 10 inches in 24 hours. On the low end (10th percentile), the models are showing 2 to 4 inches of snow in the valleys of northwest Montana and around 6 inches at mountain passes by Wednesday morning.

The long range models agree very well on a ridge building over the region starting late Saturday and Sunday. This will bring a return to valley cold pools with all the fog and stagnant air that comes with them.

AVIATION

Moist southwest flow is causing elevated snow levels and rain showers across the region. Some valley cold pools have remained persistent, mainly around terminal KGPI this morning, which has allowed for some light freezing rain from time to time and fog. However, an increasing pressure gradient and southerly winds this morning is breaking up those cold pools. Weak waves embedded in the southwest flow are interacting with the terrain causing persistent showers today. Though with the increasing wind, rain shadow effects will limit the impacts at most terminals, especially once the cold pools have been fully eroded out.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...Wind Advisory until noon PST today for Lower Hells Canyon/Salmon River Region...Orofino/Grangeville Region.