January 16, 2009 Avalanche Advisory

West Central Montana Avalanche Center
Avalanche Advisory

Posted Friday January 16th, 2009 at 0630.

This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for January 16th, 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. The advisory area includes the Bitterroot Mountains from Lost Trail to 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 National Forest Avalanche Center website.

Weather and Snowpack Analysis

All our observers yesterday agree that we now have mostly safe conditions with a few exceptions. Dangerous conditions still exist on some terrain features especially areas where the snowpack is shallow on steep rocky terrain. It doesn’t matter which way it faces the sun; some of these slopes are holding weak faceted snow on a crust near the ground which will remain for several weeks.

Temperatures were starting to climb above freezing above 7000′ Thursday and the skiing and riding conditions were very good. The overall snowpack has strengthened considerably during the past 2 weeks and the weak faceted snow at the ground that had us in a fuss is showing signs of strength and bonding. I still don’t trust it on some slopes, areas where the snowpack is thin in particular.

We are starting to see signs of surface hoar development, radiation re-crystallization and near surface faceting on the surface and on the zipper crust from last Sunday. This is not yet a problem but keep this bit of information tucked away for the next storm cycle.

Current Avalanche Danger

Throughout our advisory area the avalanche danger is LOW on most slopes and at all elevations. Natural avalanches are very unlikely, human triggered avalanches are unlikely. As you might expect there are some noteworthy exceptions to this welcome condition. Unstable slabs may exist on some terrain features such as wind loaded slopes steeper than 35° or areas where the snowpack is shallow with rock outcroppings where it would be easier to collapse through to the weaker facets near the ground.

On these slopes the avalanche danger is MODERATE. Natural avalanches are unlikely, human triggered avalanches are possible. Remember, we just came through a big avalanche cycle where the culprit was the faceted snow around the early December rain crust. It’s 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!

Weather Forecast and Avalanche Outlook

A strong ridge of high pressure is settling over the Northern Rockies increasing inversions and bringing foggy, cool conditions in the valleys and warmer sunny weather in the mountains. Temperatures are expected to reach into the low 40’s the next few days with little wind and clear skies.

These conditions will continue to strengthen our snowpack. Avalanche danger will increase on the Southerly aspects when the sun reaches its peak and temperatures rise above the freezing mark. Those aspects tend to be shallower and more prone to rapid warming at this time of year so pay close attention to the temperatures and avoid these warmer slopes later in the day. Wet snow avalanches involving the newest snow may step down to more deeply buried weaknesses once they start moving.

We continue to receive excellent observations from many different locations. Your snow observations are very important to us as they help us portray more accurate overall avalanche conditions in our area. Our resources are limited so information about avalanche activity or snowpack conditions you see may save a life. 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 19th, 2009