Mar 19, 2012 @ 6:33 am

March 19, 2012 Avalanche Advisory

There is MODERATE Avalanche Danger in the west central Montana backcountry on terrain steeper than 35 degrees and above 6000 feet in elevation.

There is LOW Avalanche Danger on all other terrain in the advisory area.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Monday, March 19th, 2012.

Weather and Snowpack Analysis

Advisory area locations picked up 7-12 inches of snow since Friday, the southern Bitterroot Mountains receiving the higher amounts. The winds were moderate out of the south and west and mountain temperatures were in the low to mid thirties during the day. Currently, temperatures are in the mid twenties, winds are out of the north and west at 5-8 mph, and it’s snowing.

The new snow we have received is bonding well to the sun crusts that developed early last week. It is settling quickly, but there are multiple weaknesses within the storm snow that are releasing easily on steep slopes with a human trigger. Watch for recently formed soft slabs and loose snow sluffs to fail easily on steep terrain. Standard sluff management techniques will work well to keep you from getting caught by the loose debris.

Look for fresh wind drifts on leeward sides of upper elevation ridges, as well as cross-loaded terrain features like gullies and sub ridges. These drifts are about a foot deep and should be mostly manageable if you are not caught by surprise.

The buried surface hoar layer, down 2-3 feet, that has been the cause of recent human triggered slides has continued to gain strength. This weak layer takes a lot of force to fail, but should still not be trusted. A slide initiated in the upper snow pack could step down to this layer. So, dig down and look for this weakness before you commit to a steep slope.

When the sun comes out this week, pay attention to how the snow is changing. It will warm the surface snow quickly and produce wet surface snow slides on the buried sun crust. When the snow starts getting damp, move off the slope in search of colder snow.

Weather Forecast and Avalanche Outlook

There is a Winter Weather Advisory posted for our advisory area until noon today. Forecasts are calling for an additional 3-8 inches of snow in the higher terrain of west central Montana. Temperatures will stay cool until Tuesday when the next storm system arrives. The wet storm pattern will stay with us delivering moderate amounts of snow until Thursday, when we should see a brief break in the active pattern.

I expect the avalanche danger to remain the same with small doses of new snow accumulations throughout the week.

Dudley will issue the next advisory on Friday, March 23rd.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at [email protected]. This information is invaluable to us and in turn comes back to you in the form of a better forecast.





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 the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.