February 26, 2013 Avalanche Advisory

There is MODERATE avalanche danger above 6000 feet on slopes steeper than 35 degrees in the backcountry of west central Montana. Natural avalanches are unlikely, but human triggered avalanches are possible.

Good Morning. This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Tuesday, February 26th, 2013.

 

Weather and Snowpack Analysis

The most recent storm has deposited 8-10 inches of new snow in the Bitterroots, southern Swans, and Mission Mountains. 3 inches of new snow fell in the Rattlesnake Mountains. Winds were gusting from 20-25 mph on ridgetops out of the south and west and day time temperatures hovered in the upper twenties. This morning there is scattered snow falling, temperatures are in the upper teens and low twenties, and winds are out of the west at 10-12 mph.

The primary avalanche concern is wind slabs that have formed on leeward slopes over the past few days. The Bitterroot Mountains, southern Swans, and southern Mission Mountains have received 15-20 inches of snow since last Friday and the winds have been blowing steadily out of the west and southwest. We have been receiving small amounts of snow for the past 2 weeks allowing the lower snowpack to adjust and strengthen. The newest snow load is sitting on a weak interface and will need some time to adjust. We received 2 separate reports of snow failing on this weak interface during stability testing near Gash Point (one report). Steve and I toured in the southern Bitterroots on Sunday and found this weak layer in the upper part of the snowpack near Saddle Mountain (profile).

The secondary avalanche concern is the possibility of failures in the new storm snow in those areas that received the higher amounts of snowfall. Variations in temperatures and precipitation rates may have created weak layers in the new snow. Ski cutting on small test slopes is a good way to determine how the snow will react on a bigger slope.

A layer of facets that is buried 1-3 feet deep has continued to gain strength, but is still clearly visible in test pits. This weakness has been reactive in some stability tests for the past month and was the weak layer involved in a human triggered avalanche in the northern Bitterroots last week.  Although mostly stable conditions can be found in many areas, this weakness should not be overlooked if you are going to ride on steep open terrain.

 

Weather Forecast and Avalanche Outlook

Today expect scattered light snow to continue with the chance of another 1-2 inches as weak high pressure builds. Winds will be out of the west in the 10-12 mph range and temperatures will be in the upper 20’s. An unsettled weather pattern will continue into the end of the week producing periods of precipitation.

I expect the avalanche danger to remain the same as we continue to receive moderate amounts of snow accompanied by winds.

I will issue the next advisory on Friday, March 1st.

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 [email protected] Thank you for your continued support!

 Education:

We have recently added a level one avalanche class that will start March 12. You can follow this link for more information, or visit our education tab on the left side of our website.