January 21, 2011 Avalanche Advisory

Good morning! This is Steve Karkanen with backcountry avalanche information for Friday, January 21, 2011.

Current Avalanche Danger

On all slopes above 5000 feet steeper than 35 degrees, the avalanche danger is MODERATE. Natural avalanches are unlikely, human-triggered avalanche are possible. It is possible to trigger small avalanches on wind loaded terrain and in some cases, where the snowpack is shallow, larger avalanches may be triggered.

All other slopes including areas below 5000 feet now have a LOW avalanche danger. Natural and human-triggered avalanches are unlikely. Be aware of unstable snow in isolated areas mostly influenced by wind and terrain.

Weather and Snowpack Analysis

The warm temperatures we experienced last week have subsided and left us with a very settled snowpack and concrete snowpack conditions. All observers in the Bitterroot and Rattlesnake mountains report mostly stable conditions and pretty good skiing and riding conditions with just a few inches of new snow on a very hard base.

The now deeply buried surface hoar that had us on edge has gained a lot of strength and is now deep enough not to be an issue anymore. There are two thick crusts within a foot of the snow surface and these will need to be watched for the next few days but the current snow has bonded strongly to the upper crust and does not appear to present any future stability problems. There is a layer of graupel within the new snow that may prove to be a weakness with heavy loading but for now it is not an issue. We were able to produce some minor sloughing on 40 degree slopes but all indications are that we now have the strongest snowpack we’ve seen this winter.

A report from the Southern Swans was indicating there may be isolated areas of instability due to high winds and cross loading in some areas so it is still important to check things out and ski conservatively if you are not certain.

Weather Forecast and Avalanche Outlook

Significant snow and high winds are expected late Friday into Saturday.

A vigorous weather system is expected to move into the advisory area late Friday and Friday night. This system will produce areas of moderate to heavy snowfall with increasing west winds. There is currently plenty of dry snow on last weeks hard snow surface available to be moved around so expect leeward terrain to be heavily loaded during passage of this system.

High pressure is expected to return later Saturday.

Expect the avalanche danger to rise in areas that receive significant snow with wind. Wind loaded terrain may have considerable avalanche danger during and immediately after the expected weather system on Saturday.

The next advisory will be issued on January 24, 2011.

Upcoming Events

On January 26th, Skip Horner, a well-known mountaineer who was the first to lead guided trips to the legendary Seven Summits, will be giving a fascinating talk and slide show to benefit missoulaavalanche.org.

This show is at the Trail Head, 221 East Front and starts at 7pm.

We have scheduled a Level 2 Avalanche class February 15-18.  This course is in response to the many requests we receive every year to provide this level of training in Missoula.  To date, 5 people have registered and we need 12 to make it happen.  More information can be found on the American Avalanche Institute website.  This is a great opportunity for those of you wanting to broaden your avalanche education.  Don’t miss it!