textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Minimal impact from light snow tonight and Saturday

- Strong Winds Sunday into Monday, with a 60 to 80 percent chance of widespread gusts over 40 mph in the valleys.

- Active Pattern for the rest of next week/weekend; potential for more wind and winter weather impacts.

Satellite imagery this afternoon depicts a broad region of high pressure off the West Coast, and low pressure over southern Alaska. These features are working together to send a long fetch of moist air into western Canada and the Pacific Northwest under northwesterly flow aloft. Although the moisture will arrive in waves for the Northern Rockies, weather will remain unsettled well into the coming week.

The first wave of moisture arrives tonight. Lack of appreciable large-scale lift will make the mountains do the work, so snow accumulations will be limited to the higher terrain and favor the long, north-south oriented ranges north of I-90 such as the Missions, Swans, and the Continental Divide in Glacier Park. Snow levels stay in the neighborhood of 4,000 ft. Travel impacts will be minimal, expect only a trace to a few inches over Lookout, Marias, and Lolo passes by Saturday afternoon.

The focus on Sunday will switch to wind. A strong upper level jet will become positioned over northwest Montana and the Idaho Panhandle by Sunday afternoon. Model soundings indicate enough instability for upper level winds to mix down to the surface, where widespread southwesterly gusts of about 30-40 mph will be commonplace. Expect more isolated gusts of 50 mph, while the higher terrain will experience gusts of over 60 mph. High winds will become reinforced by a cold front passing overnight on Sunday, so High Wind Watches for all of western Montana will remain in effect through Monday morning.

The Pacific ridge/Alaskan trough configuration will keep the upper level jet pointed at the Northern Rockies through next week into next weekend (March 14-15). The Climate Prediction Center (CPC) guidance for March 14-16 highlights a 20-40% chance of both high winds and heavy snow. While significant model variance regarding snow levels limits specific valley accumulation forecasts at this range, the period requires close monitoring for renewed winter impacts and at least moderate mountain pass travel disruptions.

AVIATION

A few light showers persist south of I-90 in northwest flow, remaining mostly terrain-focused. Expect VFR conditions at all terminals into early evening with light winds, though occasional gusts of 15-20 kts are possible in well-mixed areas.

A weak disturbance arrives after 07/0300Z, bringing moisture from a decaying atmospheric river. Expect increasing mountain obscurations and light precipitation through Saturday morning, possibly becoming a rain/snow mix in valleys by 07/1200z. Fairly widespread MVFR ceilings and visibility will likely develop across northwest/west-central Montana, including KGPI and KMSO. Brief drops to IFR category are possible under heavier showers. While shower activity will continue into the afternoon, it will become more focused over the terrain after 07/1800z. Mechanical turbulence near ridge top levels is possible late tonight and early tomorrow morning as ridgetop winds increase to around 40 kts. KBTM in particular may have concerns with LLWS. Winds will become more widespread and gusty between 15 to 25 kts in the afternoon as the atmosphere destabilizes.

MSO WATCHES/WARNINGS/ADVISORIES

MT...High Wind Watch from Sunday afternoon through Monday morning for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region... Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region...Missoula/Bitterroot Valleys... Potomac/Seeley Lake Region...West Glacier Region.

ID...None.