textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Unsettled, cool, and showery conditions persist through the weekend.

- Mountain snow tonight and on Sunday will create difficult conditions for backcountry recreation, especially along the Continental Divide.

- Widespread frost and freezing temperatures Sunday through Tuesday mornings.

Radar returns early this afternoon are revealing scattered showers across the Northern Rockies. Isolated lightning strikes over north-central Idaho will migrate into northwest and west-central Montana as the afternoon evolves. Marginal instability/shear will keep thunderstorms on the weak side, producing isolated lightning and outflow winds to about 30-40 mph. Looking to the larger scale, satellite imagery is depicting a trough of low pressure approaching the Idaho Panhandle. This system will bring widespread cooler temperatures and moisture through Sunday morning. Temperatures will drop enough to support snow above about 4500 this evening. That number will drop overnight, allowing snow to reach valley floors by Sunday morning. Higher elevation valleys of southwest Montana such as Butte could see a modest accumulation by Sunday morning. The primary impact, however, will be the higher elevations along the Continental Divide, as well as the Bitterroot, Mission, and Anaconda/Pintler ranges where 4-12 inches of storm total snow (ending Monday morning) are in the forecast. Those planning on traveling above about 5000 feet in elevation should be prepared for winter-like conditions. Winter Weather Advisories are in effect for several forecast zones in Montana above 5000 feet.

The cold air associated with the approaching low will result in colder than normal overnight low temperatures. Frost Advisories are in effect for Sunday and Monday mornings. Confidence for frost is higher for Monday morning. Sky cover tonight may keep temperatures above what is conducive for widespread frost. Nevertheless, if sensitive vegetation is a concern, it would be worthwhile to take necessary precautions. Another frost advisory for Tuesday morning will not be out of the question, we will reassess on Sunday.

AVIATION

Scattered showers this afternoon will create periods of decreased visibility down to about 4 SM, and ceilings to about 2500 feet. There's about a 10% chance for isolated lightning strikes in the vicinity of KGPI and KMSO through this afternoon. Expect widespread precipitation to obscure terrain across the entire Northern Rockies airspace. Precipitation turns to snow tonight above about 5000 ft MSL. Snow levels descend overnight, with snow possible for KBTM by Sunday morning.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory from midnight tonight to midnight MDT Sunday night for Bitterroot/Sapphire Mountains... Butte/Blackfoot Region...Potomac/Seeley Lake Region...West Glacier Region.

Frost Advisory from 8 PM this evening to 9 AM MDT Sunday for Flathead/Mission Valleys...Missoula/Bitterroot Valleys.

Frost Advisory from 8 PM Sunday to 9 AM MDT Monday for Flathead/Mission Valleys...Missoula/Bitterroot Valleys.

ID...None.