January 23, Avalanche Advisory

West Central Montana Avalanche Center
Avalanche Advisory
Posted Friday January 23rd, 2009 at 0630.

Good morning! This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for January 23rd, 2009. 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 you can expect avalanche conditions to remain similar unless weather conditions change significantly. Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to near Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. More detailed avalanche information about the St. Regis Basin can be found on the Idaho Panhandle Forest Avalanche Center website.

This advisory is in memory of Ben Richards of Missoula, who died in an avalanche near Big Sky, MT 2 winters ago.

Weather and Snowpack Analysis

Temperatures this past week climbed into the 50’s above 6000′ while valley and mountain locations below about 6000′ remained cool. Sunny days and cold clear nights were the rule until Thursday when a weak weather system brought cloudy skies and wind into the area.

East and South aspects warmed enough to go through several melt-freeze cycles which left a bomb-proof crust on everything. Snow conditions are firm on the other aspects and the snowpack settled further during the warmer weather. Observers are noting faceted crystals underneath the sun crust and mature depth hoar at the ground. The facets under the crust are due to a steep temperature gradient in the upper 10cm of the snowpack. This weakness will need to be watched during the next big storm.

As far as the rotten snow at the ground is concerned, we’ve been talking about this all winter and it just isn’t going away anytime soon. The warmer weather helped glue things together now that it’s cold again but those facets at the ground are pretty well insulated and remain a concern on some slopes. Areas that have shallow or thin snow cover are the most susceptible to failure at this level but it takes a lot of force. We were only able to produce failures on pockets of shallow snow (less than 100cm) on East and West aspects.

You can view 2 good examples of this on these YouTube videos:

Video 1

Video 2

Current Avalanche Danger

The avalanche danger is MODERATE above 6000′ in areas where the snow is thin. These are typically found on East, South and West facing aspects. Natural avalanches are unlikely, human triggered avalanches are possible. At all other locations and elevations throughout our advisory area the avalanche danger is LOW. Natural avalanches are very unlikely, human triggered avalanches are unlikely. Low avalanche danger does not mean no avalanche danger.

Weather Forecast and Avalanche Outlook

Temperatures will continue to fall as arctic air moves into the area. Little snowfall is expected Friday with a possibility of accumulating snow Saturday and Sunday.

Expect avalanche conditions to remain similar until we receive significant snowfall. The weak, sugary, rotten snow that formed during the cold weather in December is still there, you can find it on most aspects between 6000′ and 9000′ and you can never completely trust it. Although we’re saying the avalanche danger is now low to moderate, it’s still possible to rip out a massive slab with the right amount of force in just the right place. So what do you do? Simple! Go one at a time!

If you have any information you’d like to share or have questions about anything related to snow safety, please contact us at [email protected].

The next avalanche advisory will be posted Monday, January 26th, 2009.