Mar 28, 2011 @ 6:42 am

March 28, 2011 Avalanche Advisory

The avalanche danger is MODERATE on wind loaded terrain steeper than 35 degrees above 6000 feet in the west central Montana mountains. Natural avalanches are unlikely and human triggered avalanches are possible.

The avalanche danger is LOW on all other terrain above and below 6000 feet in the west central Montana mountains. Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Good Morning. This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Monday, March 28th, 2011.

Weather and Snowpack Analysis

The weekend weather was typical of this time of year. Sun and snow. Advisory area locations picked up 4-8 inches of new snow over the weekend with the northern locations receiving the greater amounts. Friday and Sunday storms came in from the southwest with winds in the moderate range. Saturday’s winds blew from the east gusting into the low 30’s at upper elevations. High temperatures were recorded in the upper 30’s and low 40’s. Currently, temperatures are in the low 20’s, winds are blowing out of the west and northwest 5-7mph, and light snow is falling in some areas.

We have a deep and mostly stable snowpack in the west central Montana mountains. Avalanche concerns remain within the new snow that has drifted on upper elevation leeward aspects and cross loaded gullies.

We are in a typical spring pattern with sunshine and snow storms taking turns at bat. The north and west aspects have been spared a sun crust to this point and this is where you will need to pay attention. Watch for recently formed soft slabs and loose snow sluffs to fail easily on steep terrain. The north and west aspects are also where you will find the softest skiing and riding conditions right now. All other aspects have received a sun crust and are generally stable. Some aspects have a supportable crust while on others it remains breakable.

As temperatures warm this week, you will want to pay attention to how the snow is changing. One of our snowpits on Sunday was in a rocky area on a north slope at 7000 feet and was very close to isothermal. Other than the top 20cm, the snowpack was all at the same temperature of 0 degrees celsius. This condition can result in snow failures to the ground. We were getting failures in the moderate range in some of our stability tests deep in the snowpack.  When the sun comes out and temperatures rise keep an eye on how the snow is changing and stay off and out from underneath any steep exposed terrain.

Spring conditions bring good travel and steep recreation opportunities. Remember to stick to safe travel protocol when recreating in avalanche terrain.

Weather Forecast and Avalanche Outlook

An unsettled weather pattern will persist this week. A series of pacific storm systems will bring light snow accumulations and near normal temperatures to mountain areas. Expect 1-2 inches of new snow today and then another 2-4 inches Tuesday afternoon and evening. Weak high pressure will be present between storms.

The storm snow has time to bond and settle between systems in this type of weather pattern. So, I expect the avalanche danger to remain the same for the next few days.

This is our last Monday advisory for the 2011 season. We will issue a Friday advisory for the next 2 weeks.

Dudley will issue the next advisory on April Fool’s Day Friday, April 1.

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]. 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.