textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Lingering Hazards: Mountain snow and valley rain showers will persist through today.

- Fog Potential: Dense fog and low clouds are expected in valleys each morning from Saturday through Monday.

- A weak to moderate Atmospheric River arriving Monday through Wednesday.

Light to moderate snow will continue to create slick conditions on Highway 2 from West Glacier to Marias Pass in northwest Montana through early tomorrow. Arctic air will remain trapped against the Continental Divide, blocked by strong westerly winds aloft. Elsewhere across the region, expect persistent light showers as the remnants of this week's atmospheric river slowly move out of the area.

High pressure will build over the Northern Rockies tomorrow, bringing a brief period of dry conditions. However, due to recent moisture, fog and low clouds are expected to develop each morning through Monday. Valleys in western Montana and north-central may see dense fog at times, so plan accordingly for weekend travel.

A prolonged atmospheric river is expected to impact Western Montana and North-Central Idaho again from Monday afternoon through Wednesday, bringing moderate to heavy precipitation. Snow levels will start around 7,000 feet on Monday before falling to valley floors behind a cold front early Wednesday.

Before snow levels fall, precipitation will fall as rain for most areas. The forecast calls for 1 to 2 inches of rain in the valleys of Lincoln, Mineral, and Sanders counties in western Montana, as well as Clearwater and Idaho counties in Idaho. Mountains in these regions could see 2 to 3 inches of precipitation. Areas further south and east in western Montana will likely see 1 inch or less. A high-end scenario could bring totals 1 to 2 inches higher than the estimates given above for northwest Montana and north-central Idaho.

Impacts: Due to already saturated ground, particularly in northwest Montana, this rainfall increases the risk of rockslides, landslides, sharp rises on streams and rivers, and minor flooding. Please continue to monitor forecast updates and active Flood Watches as this system approaches.

Moisture will continue to stream over the Northern Rockies behind the cold front on Wednesday, turning rain to snow down to valley floors for the rest of the week. While 1 to 2 feet of snow is possible in the mountains, valley accumulations will vary significantly as most snow will fall in narrow bands.

AVIATION

The remnants of an atmospheric river will continue to bring light valley rain and mountain snow showers through the evening. Periodic visibility reductions can be expected for all aviation sites. High pressure will build over the Northern Rockies Saturday into Monday, leading to the development of valley fog and stratus each morning. Fog may become dense at times, with visibility dropping to 1/2SM or 1/4SM during morning hours at KGPI (Kalispell), KMSO (Missoula), and KHRF (Hamilton).

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until 5 AM MST Saturday for West Glacier Region.

ID...None.