Jan 31, 2011 @ 6:43 am

January 31, 2011 Avalanche Advisory

Good Morning. This is Tim Laroche at the West Central Montana Avalanche Center with backcountry avalanche information for Monday January 31st, 2011.

Current Avalanche Danger

On slopes steeper than 35 degrees on all aspects above 6000 feet the avalanche hazard is MODERATE. Natural avalanches are unlikely, human-triggered avalanches are possible. On all other terrain above and below 6000 feet, the avalanche hazard is LOW. Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Weather and Snowpack Analysis

Storm totals throughout our advisory area differed dramatically from North to South. The northern part of our area received just over 12 inches of fresh snow while the southern area received only 1-3 inches over the past 48 hours. The winds remained fairly light in the mountains while strong North and East winds blew hard at lower elevations. Temperatures dropped significantly yesterday and mountain temperatures are currently in the single digits and the winds are light out of the northwest.

At higher elevations yesterday the winds remained light, which allowed the storm snow to distribute itself uniformly on all aspects. The snow came in warm and continued to cool making for a “right side up” snow storm. This type of storm system makes for great skiing and riding under mostly stable snowpack conditions.

On our tour of the southern Swan Mountains on Sunday we found the snowpack to be well settled and mostly stable. Observers in other areas are reporting similar conditions. The new snow was bonding well to the old snow surface, although it was very easy to produce significant sluffs on steeper terrain. We found the buried surface hoar layer that formed January 22nd and were getting stability tests in the moderate range on this weak layer. The facets are beginning to break down and this layer is gaining strength, but could be a factor on steep open slopes. This weak layer is not widespread but has been found on all aspects above 6000 feet in areas of the Swans and throughout the Bitterroot Range.

If wind speeds start to increase, pay close attention to wind slab development. The upper part of the snowpack is light and fluffy and will get transported easily forming sensitive wind slabs on leeward slopes and terrain features.

Weather Forecast and Avalanche Outlook

Drier arctic air will settle over our region through Wednesday. This will result in clear and cold conditions. Temperatures will slowly trend upwards throughout the week and wind should remain light at upper elevations. Current forecasts are calling for the next significant storm system to arrive by the end of the week.

I expect avalanche conditions to remain the same through the week.

The next advisory will be issued Friday, February 4th.

If you get out, please send us a note with what you are seeing by using our “Public Observations” form under the “Submit an observation” link on our website.

February 1 and 2 is our free avalanche workshop. For more information on this event please follow this link. Awareness Workshop


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.