January 11, 2013 Avalanche Advisory

There is HIGH AVALANCHE DANGER on wind-loaded terrain steeper than 35 degrees above 6000 feet in the west central Montana backcountry. The avalanche danger is CONSIDERABLE on all other terrain in our advisory area.

Good Morning! This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Friday, January 11th, 2013.

 

Weather and Snowpack Analysis

Scattered snowfall has continued overnight and this week’s storm has left 12 to 21 inches of new snow in the mountains of west central Montana. The winds blew steadily from 10-20mph yesterday mainly from the north and west. Temperatures continue to drop. Currently it is snowing lightly, winds are generally light out of the north and west, and temperatures are hovering in the single digits in most locations.

The old snow surface from last week’s dry weather that is now buried 1-2 feet deep has indeed created a fragile weak layer for the new storm snow to slide on. All of our observers reported clean shears on this layer of buried facets in stability tests, the Snowbowl ski patrol reported high energy slides during control work yesterday morning, and Dudley and I found multiple natural slides and widespread collapsing and shooting cracks in the Bitterroot Mountains near the Brushy Fork of Lolo Creek.

The temperatures dropped yesterday creating low density surface snow that will transport easily, continuing to load leeward aspects. Therefore, the primary avalanche concern is wind slabs that continue to develop on leeward aspects adding depth and weight to a sensitive slab. The secondary avalanche concern is storm slabs that are also resting on the weak faceted layer of snow in areas that have not been affected by the wind. Stay off and out from underneath steep terrain until the new snow has had time to settle and stabilize. This will not happen quickly with the widespread and persistent weak layer we are now dealing with. The bright side is that we have a very strong and supportive snowpack below the new storm snow.

Our latest storm started with warm temperatures that have now cooled significantly. The snow has continued to fall and the primary riding surface is now very low density snow. This condition allows for excellent riding opportunities on low angle terrain. Be conservative in your decision making and don’t let the lure of deep powder dreams lull you into riding on a steep, unstable slope.

 

Weather Forecast and Avalanche Outlook

Today expect light snow to continue with the chance of another 1-3 inches of accumulation before the storm finally exits to the east tonight. Winds should be in the 5-10 mph range mainly out of the north and temperatures will remain cold with highs in the low teens and lows in the single digits.

I expect the avalanche danger to slowly decrease over time, but the cold weather will continue to maintain the weak faceted layer that is our primary concern.

Dudley will issue the next advisory on Tuesday, January 15th.

Make plans now to join us on Wednesday, January 16th for Community Unite Pint Night at the Northside Kettle House. Proceeds help to benefit the West Central Montana Avalanche Foundation. 5-8pm

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!