Mar 5, 2012 @ 6:49 am

March 5, 2012 Avalanche Advisory

There is MODERATE avalanche danger above 5000 feet in the west central Montana backcountry. Small avalanches in specific areas; or large avalanches in isolated areas.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Monday, March 5th, 2012.

Weather and Snowpack Analysis

Spring rolled in this past weekend and mountain temperatures soared into the low to mid forties on Sunday at all advisory area locations above 6000 feet in elevation. Winds blew hard out of the west and south most of the weekend gusting into the 50mph range in some locations. Currently, temperatures are in the low to mid thirties and the winds are out of the south and west at 8-10 mph under partly cloudy skies.

The sun crust that formed a week ago is now providing a slick sliding surface for the new snow that we received late last week. This crust is most pronounced on south and east aspects. The new snow of 6-10 inches is failing easily in our stability tests on these aspects during this period of warm weather. This condition however, is not a big concern unless a slope fails on a persistent weakness deeper in the snowpack. This is not likely, since it is taking a lot of force in our stability tests to get it to fail.

North facing aspects do not have the sun crust in the upper snowpack, and this is where you will find the softest snow. These aspects are staying cool at upper elevations and providing the best opportunity for recreation. The concern on these slopes is the buried surface hoar layer that is down 2-3 feet. This weakness has gained strength the past few weeks and stability tests have consistently been improving. You will still want to look for this weakness before riding a steep open slope.

Now that warmer temperatures have arrived it is important to pay attention to how the snow is changing during the day, and even hour by hour. You will want to move off steep terrain once the snow becomes damp. Temperatures remained warm last night so look for snow conditions to deteriorate quickly today. Temperatures will cool significantly tonight with the arrival of a cold front and this will help to improve avalanche conditions. When the warm temperatures return later this week, be sure to pay attention to dormant weak layers becoming more reactive, weakening cornices, and for point release slides on steep solar aspects.

We received a report late last night of a live recovery of a snowmobiler caught and buried in a slide near Seeley Lake. The details are vague and Steve will be up there today to investigate. He will post more information on our website under the Documents/Accident Reports tab.

Weather Forecast and Avalanche Outlook

Mountain temperatures will warm into the forties this afternoon and southwest winds will increase ahead of a cold front arriving tonight. The cold front could bring 5-10 inches of new snow by Tuesday morning with gusty west winds to 40 mph. Cooler temperatures and a few lingering snow showers are forecast for Tuesday. Then, a ridge of high pressure builds over our area starting Wednesday bringing rising temperatures through the end of the week.

I expect the avalanche danger to increase with the new snow load followed by warming temperatures.

Dudley will issue the next advisory on Friday, March 9th.

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.