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Avalanche warning in effect in west-central Montana

Published On: Jan 09 2013 10:23:21 PM MST
MISSOULA, Mont. -

The following is a press release from the West Central Montana Avalanche Center:

An avalanche warning is now in effect for the mountains of west central Montana

The combination of heavy, wet snow and sustained winds for the past 36 hours has heavily loaded leeward slopes in our advisory area and has created dangerous avalanche conditions. There is a High Avalanche Danger and travel in avalanche terrain is not recommended.

Good Evening. This is Tim Laroche with an avalanche update from the West Central Montana Avalanche Center.

Weather and Snowpack Analysis

Snotel sites are showing a significant increase in snow water equivelent over the past 36 hours. .4? in the southern part of our advisory area to 1.4? in the northern Bitterroots to .8? in the southern Missions and Swans. Snow amounts in the 6-12 inch range. The winds have been blowing steady 15-20mph out of the west and southwest. Temperatures have been in the low to mid thirties and are finally starting to fall. The snow level has been hovering around 5500? and will fall tonight.

Last week’s weather left behind a myriad of weak snow surfaces including surface hoar, near surface facets, sun crusts, wind crusts, and a thin freezing rain crust in some locations. Now all the heavy wet snow is sitting on top of these old surfaces. Some may bond well, but others may not. You will need to be paying attention to all the red flag warnings of avalanche danger.

The primary avalanche concern is fresh wind slabs that have formed on leeward aspects and cross-loaded gullies. The past week’s weather helped continue to settle and strengthen our snowpack, but it created a weak snow surface in many locations. Strong southwest winds have created fresh drifts on leeward terrain and will be sensitive. Yesterday, we observed weak faceted snow getting buried on an east aspect. This was not a major concern at the time, but will be if it is buried by a fresh drift or storm slab. Pay attention to how the snow is reacting. Watch for shooting cracks and whumpfing for sure signs of instability.

The secondary avalanche concern will be storm slab avalanches on all aspects as we continue to receive more snow. Dig down below the storm snow to see how it is bonding to the old snow surface before you commit to a slope. Pay attention to obvious clues of instability like recent avalanche activity, periods of intense precipitation, strong winds transporting snow, or the feel of a “slabby” snowpack. Move off and out from under steep terrain until the storm snow has had time to settle.

All of our observers and avalanche specialists will be out on Thursday to collect more data.

Weather Forecast and Avalanche Outlook

The snow level will drop dramatically tonight, but the precipitation should continue. The winds will turn to the north and northwest and continue to blow in the 10-20mph range. Most advisory locations should pick up another 5-15 inches of additional snowfall by Friday morning.

With persistent weak layers getting buried by a lot of dense snow, I would suspect the avalanche danger will be slow to moderate.

I will issue the next regular advisory on Friday, January 11th.

Make plans now to enjoy Community Unite at the Kettle House on January 16th. Proceeds help to benefit the West Central Montana Avalanche Foundation.

If you get out and have the time to send us some information about what you are seeing, please use our “public observations” link on our website or send us a quick note at info@missoulaavalanche.org. Thank you for your continued support!

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but you can use the information we provide to help you make more informed decisions regarding travel in avalanche terrain for the next few days.

Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake.