Jan 28, 2011 @ 6:34 am

January 28, 2011 Avalanche Advisory

Good morning. This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday January 28th, 2011.

Current Avalanche Danger

Throughout our advisory area the avalanche hazard is generally LOW. Natural and human triggered avalanches are unlikely. However, there are pockets of  MODERATE avalanche hazard for triggering a wind drift on steep slopes. These wind drifts can mostly be found on exposed ridges above treeline. There are also pockets of MODERATE hazard for loose, wet sluffs on steep, sun exposed slopes during the warmest parts of the day. In these pockets, natural avalanches are unlikely and human triggered avalanches are possible.

Weather and Snowpack Analysis

We have received 3-5 inches of new snow in most mountain locations since our last advisory. Winds have been blowing a steady 10-20 miles per hour out of the South and Southwest at upper elevations for the past 3 days. Daytime temperatures have been in the mid thirties and nighttime temperatures have only cooled a few degrees from that. Currently, temperatures are in the upper 20’s to low 30’s and the winds are 3-5 out of the South and Southeast.

The warm temperatures have continued to help settle and strengthen our snowpack over the course of the past week. On our tour in the Hoodoo Basin on Thursday, we found very stable conditions to exist on all aspects. The melt/freeze crust that is now buried 50cm’s deep and has been observed in all locations is very hard and the snow on top of it continues to bond well to it. The buried surface hoar layers that were of concern to us earlier in the season are now buried well below this bombproof crust and are no longer a factor to slope stability. All of our observers throughout the advisory area are reporting similar conditions.

The main stability concern right now is the sensitive wind drifts that have formed on exposed ridgetops at elevation. These drifts are mostly found on leeward aspects that have cornice development. While getting mostly stable conditions in our snow pits, we are able to easily propagate fractures while ski cutting where these wind drifts have formed(photo). Use caution when skiing or riding near such features.

The warm temperatures that we will see again today will continue to produce localized areas of wet sluffs on steep, sun exposed slopes. Plan on getting off the warm aspects when you start to see this activity occurring.

There is a buried surface hoar layer in the upper part of the snowpack that formed last weekend(now buried 10-20cm’s). Most of our observers reported seeing this weak layer and were getting easy to moderate failures during stability tests. This weakness will need to be monitored when we get another dump of snow.

Weather Forecast and Avalanche Outlook

Today we will remain under the influence of a weak ridge of high pressure. A system will move through the area tonight and produce some light snow with 1-2 inches of accumulation. Late Saturday we will see a stronger system that could bring significant winds and should produce snow amounts in the 3-5 inch range. Temperatures should begin to cool Saturday night into Sunday.

If the next storm systems come in with more precipitation than forecasted and strong winds, expect the avalanche hazard to increase. Otherwise, I expect conditions to remain the same.

The next advisory will be issued on Monday Janurary 31st, 2011.

If you get out, please send us a note with what you are seeing by using our “Public Observations” form.

Thank you to all of you that came out to enjoy Skip Horner’s presentation on Wednesday evening and for the continued support of the avalanche program in your community.


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.