Mar 22, 2013 @ 6:15 am

March 22, 2013 Avalanche Advisory

MODERATE avalanche danger exists on wind loaded terrain steeper than 35 degrees above 6000 feet throughout the west central Montana backcountry. Small avalanches in specific areas; or large avalanches in isolated areas.

The avalanche danger is LOW on terrain that does not have a wind load and is less steep than 35 degrees. Small avalanches in isolated areas or extreme terrain.

Good Morning. This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Friday, March 22nd, 2013.


Weather and Snowpack Analysis

All advisory area locations picked up fresh snow the past few days. Most mountain locations picked up 4-7 inches of new snow since Wednesday. The wind blew hard from the west and southwest, gusting into the 40 mph range at times (photo). Temperatures hovered in the twenties. This morning at 4am, winds have calmed to 4-6 mph out of the west and southwest, temperatures are generally in the teens, and widely scattered light snow continues to fall.

The relentless wind this past week created soft and hard wind slabs on leeward slopes and terrain features at upper and mid elevations. During stability testing, we are getting the soft slabs to fail on a melt-freeze crust that is buried 1-2 feet deep. These 3 pit profiles highlight the layer of concern in 3 different locations (profile, profile, profile). This weakness is mostly found on the coldest aspects of north and northeast that have not experienced the sun exposure that other aspects have this past week. These are also the aspects that received the most wind load and where you will find the softest skiing and riding at upper elevations. The hard wind slabs that formed are smooth, rounded, and hollow sounding and can be found on multiple aspects. They will be stubborn to trigger, but could break 1-2 feet deep and well above you on a slope.

The secondary avalanche concern is for loose snow avalanches in steep terrain. The new snow we are receiving is coming in cold and will easily sluff on the buried melt-freeze layers that formed this past week. When the sun comes out, it will quickly warm the new snow and loose wet slides will be a concern on aspects exposed to the sun. These conditions are generally manageable, but should not be over-looked if you are recreating in high consequence terrain.

The snow and wind we have been receiving continues to add weight to the hefty cornices that now hang above leeward slopes. These tend to break further back than one might expect. Use caution when recreating around these features.


Weather Forecast and Avalanche Outlook

Cold temperatures and scattered snow showers will stick around through the weekend, but we should see much less wind than recent days. Most advisory area locations should receive another 2-4 inches of new snow. High temperatures will be in the twenties and lows in the teens to single digits. Winds will be out of the northwest at 6-10 mph.


Cold temperatures will likely help to keep the upper snow pack instabilities weak. Therefore, I expect the avalanche danger to remain at the MODERATE level.


Steve will issue the next advisory on Tuesday, March 26th.


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!


Have a Great Weekend!




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.