textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- High-Impact Snow Squalls This Afternoon & Evening: Increasing threat for gusty winds, whiteout conditions, and icy roadways, especially along and near I-90 Lookout Pass to Homestake Pass and Highway 12/200.

- Cold Start on Sunday: After the cold front passes, expect morning temperatures in the teens and 20s in Idaho and single digits to teens in western Montana.

- Snowy Monday Morning Commute: A warm front will lead to increasing moisture Sunday night into Monday morning, bringing a snowy start to the work week for many valleys.

- Late-Week Warm-Up: A strong high-pressure ridge will push temperatures into the 50s and 60s by mid-week.

The cold front is currently tracking south from Canada, marking the end of the recent atmospheric river and bringing a much colder air mass to the Northern Rockies. Today, as the front interacts with lingering moisture and afternoon instability, we expect scattered snow showers to develop. Of particular concern are snow squalls along the I-90 and Hwy 200 corridors by this evening. These can cause sudden, near-zero visibility and a flash freeze on roads that were wet earlier in the day.

Sunday starts cold but relatively quiet under a brief ridge of high pressure. However, this reprieve is short-lived. By Sunday night into Monday morning, a warm front will push into the region. With cooler air in place, precipitation will likely start as snow for most valley locations. This will make for a snowy Monday morning commute, especially for northwest Montana and the Missoula/Bitterroot valleys, before snow levels gradually rise and transition to rain by Monday afternoon.

By Wednesday and Thursday, afternoon highs are progged to soar 15-20 degrees above seasonal averages, with lower valleys likely reaching the mid-60s. While the ridge will provide significant stability, moisture streaming over the ridge crest, often referred to as dirty ridge, will likely result in periods of cloud cover and isolated showers.

AVIATION

Snow squalls and gusty winds are the main aviation concerns through this evening, as an Arctic front moves south across the region. Valleys will see wind gusts commonly between 30-40 knots. The primary hazard will be convective snow squalls between 21Z and 04Z, which may cause sudden drops in vertical visibility (VV002) and horizontal visibility below 1/2SM. Mountains will be frequently obscured in clouds and snow. Conditions will briefly improve Sunday morning under a transit ridge, but a second round of MVR/IFR conditions is expected Sunday evening as widespread overrunning snow develops ahead of an approaching warm front, maintaining low ceilings and reduced visibilities through midday Monday.

MSO WATCHES/WARNINGS/ADVISORIES

MT... Winter Weather Advisory until midnight MDT tonight for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region... Lower Clark Fork Region...Missoula/Bitterroot Valleys... Potomac/Seeley Lake Region.

Winter Weather Advisory until 6 PM MDT this evening for Flathead/Mission Valleys.

ID...Flood Watch until 5 PM PDT this afternoon for Lower Hells Canyon/Salmon River Region...Northern Clearwater Mountains...Orofino/Grangeville Region...Southern Clearwater Mountains.

Winter Weather Advisory until 11 PM PDT this evening for Southern Clearwater Mountains.

Wind Advisory until 9 PM MDT this evening for Eastern Lemhi County...Western Lemhi County.