Mar 15, 2013 @ 6:31 am

March 15, 2013 Avalanche Advisory

The avalanche danger in the west central Montana backcountry is MODERATE. Warm temperatures at higher elevations have weakened the snowpack. With temperatures above freezing at elevations 6000 feet and higher, there is the possibility of loose, wet snow avalanches on slopes that are 35 degrees and steeper. If it rains above 6000 feet the immediate impact of the rain will destabilize the snow. On slopes below 6000 feet and less steep than 35 degrees the avalanche danger is LOW.

Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s advisory for Friday March 15, 2013.

Weather and Snowpack Analysis

Mountain temperatures did not reach the freezing point last night. Temperatures are in the thirties and forties. High elevation winds are strong out of the west and southwest gusting 20 to 30mph. The winds aren’t moving snow though, the warm temperatures have made things quite heavy. The warming has lasted a few days. Many mountain locations in the region have stayed above freezing for over 48 hours.

The warm temperatures have settled out the wind-slab potential but made the surface snow quite weak. I observed lots of debris in the Rattlesnakes yesterday from ubiquitous loose, wet snow releases (photo 1) (photo 2).  Observers in the Lost Trail area noted debris from loose, wet avalanches on steeper slopes. Most of the wet releases at Lost Trail and in the Rattlesnakes were observed on slopes with northerly aspects. Steve was in the Bullion Pass area (southeast of Lookout Pass) and found loose, wet unconsolidated snow also.

We had a second hand report of wet avalanches that ran to the ground in the southern Swans. Steve did find water pooled on crusts in the snow and near the bottom of the snowpack in his pits southeast of Lookout Pass. This is something to keep in mind on very open, big unanchored slopes.

The Bottom Line

The Moderate danger is related to terrain and timing. On slopes steeper than 35 degrees, expect the danger of wet slides to elevate during the warmest part of the day.  Rain above 6000 feet will also increase the avalanche danger.  The chances for cornice failure increase as the warming causes the entire snowpack to creep downhill.

Weather Forecast and Avalanche Outlook

Forecasts call for temperatures to be a few degrees cooler today. Rain is predicted for up to 6000 feet on Saturday; then a return to winter may happen (weather story). The colder temperatures will stiffen things up and likely stabilize the snowpack. Snow is expected to accompany this change in the weather; time will tell if the weekend system produces enough snow to create surface instability. New snow would be welcome; with the warm temperatures we’re experiencing, and the cold change predicted, backcountry skiing and riding conditions might prove challenging.

Public Observations

I would like to extend a note of thanks to all those who have sent in observations. Some are posted on the website; some folks request they not be posted. Some of the observations are just quick e-mails from an iPhone. The one thing they all have in common is they are valuable.

Consider sending in observations either this season or next. You can be vague about the area; maybe just name a drainage, aspect and elevation. The more info we have, the better the advisories. Observations aren’t for the avalanche center; they’re for your compadres. If you would like to report on avalanche or snow conditions use our public observations form or send us a note at [email protected] .

Tim will issue the next advisory on Tuesday, March 19.

Ski and ride safe and have a great weekend.


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.