February 8, 2013 Avalanche Advisory

The avalanche danger is at the MODERATE level (level 2) in the west central Montana mountains.  Natural avalanches are unlikely but human triggered avalanches are possible.  Heightened avalanche conditions exist on wind loaded terrain steeper than 35 degrees and in isolated areas where the snowpack is shallow.  Carefully assess the terrain and snow to identify features of concern.

Hello!  This is Steve Karkanen with the West Central Montana Avalanche Center’s (WCMAC) avalanche advisory for Friday, February 8, 2013.  This advisory is made possible through the cooperative efforts of the Lolo, Bitterroot and Clearwater National Forests, the Missoula Office of the National Weather Service and the West Central Montana Avalanche Foundation; a 501 c (3) non-profit organization whose mission is to support the avalanche advisory and education efforts of the WCMAC.

 

Weather and Snowpack

Since Monday, our advisory area received little snowfall and mountain temperatures stayed in the twenties. Winds continue to rake the higher elevations but very little snow has been available for transport. It’s been a week since the last significant snow.

Stability tests and snow profiles at all the sites we’ve visited in the north and south Bitterroot mountains, Southern Swans and Rattlesnake show continued strengthening. Currently, the main avalanche problem is wind slab development on steep leeward terrain. These fresh slabs are shallow now but are touchy and may be a bigger problem with additional snow.

The bigger wind slabs that formed during and after the last big storm appear to have gained a lot of strength over the past few days but it is always a good idea to be wary of them.

The secondary avalanche problem is the persistent layer of facets that formed during the MLK holiday weekend. This slab, now two to three feet deep, fails cleanly when a great deal of force is applied in compression tests but they are not propagating in extended column tests.

In the Hoodoo Pass area there are large glide cracks on several of the steep open east facing slopes along the state line.  These are disconcerting in that they are clear evidence that the snow wants to move downhill and are extremely unpredictable.  We’ve seen several soft slabs pull out around these deeper glide cracks recently. The best thing to do around these features is to avoid them especially during periods of rapid warming.

The weakest snow we see now is on the more exposed aspects that have shallow snow. These are isolated pockets and tend to be in areas that we rarely recreate on.  Before you jump into a steep starting zone, check out the snow depth with a probe.  If the snowpack is less than 3 feet deep, it may have a weak structure at it’s base and you should be able to feel that weakness with your probe.

 

 

Weather Forecast and Avalanche Outlook

A weak storm system will move through the northern Rockies today with light mountain snowfall anticipated. Limited moisture aloft and weak forcing will limit snowfall amounts this weekend as another storm system passes through the area. The Missoula Weather Service Office is projecting a similar pattern for the next few days with small amounts of snow during the period.

A little snow with each storm will not affect the current stability.  Our mountain snowpack is trending toward LOW avalanche danger.  All the indicators tell us that we have a mostly stable snowpack but we still see some potential on very steep wind loaded terrain and in isolated areas that have a shallow snowpack, hence the MODERATE danger rating.

Expect new wind slab formations on leeward terrain.  The earlier layers of concern are much stronger this week but do fail cleanly and with energy when they do fail. It’s a low probability-high consequence scenario that deserves respect.

Use the time honored technique of one-at-a-time whether you are on a sled, a snowboard, riding up or skiing down, and you will be less likely to disturb a monster.

Dudley Improta will issue the next advisory on Fat Tuesday, February 12.

Send us your observations!  We do read them and are valuable to the rest of the community.  If you don’t want the information posted, we respect that, we just want to know what people are seeing out there.  We cover a huge area and can’t possibly visit all the terrain people are skiing and riding in.  You can post an observation on our Public Observation link or simply send an email message to [email protected]

Have a safe weekend!