Jan 24, 2011 @ 6:47 am

January 24, 2011 Avalanche Advisory

Hello! This is Steve Karkanen with backcountry avalanche information for Monday, January 24, 2011.

Current Avalanche Danger

On all slopes above 5000 feet, the avalanche danger is MODERATE. Natural avalanches are unlikely, human-triggered avalanche are possible. There are heightened avalanche conditions on some terrain features.

Above 7000 feet, the higher elevations were getting blasted by westerly winds approaching 30 mph on the ridgelines above treeline. It is possible to trigger small avalanches on this 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 that have been influenced by wind and terrain.

Weather and Snowpack Analysis

The primary avalanche concern is wind slab development in areas exposed to high W-NW winds the past couple of days.

W-NW aspects have been scoured and stiff wind slabs have formed on leeward slopes in many areas. These wind slabs can be very touchy and can take you for a nasty ride if you get caught in one. These can be found mostly above 7000 feet on E-SE aspects. Once you drop a few yards below ridgeline out of the wind, the snow turns back to fluff and is quite good.

The overall snowpack is in a mostly stable condition. The new snow is bonding well to the hard melt-freeze layers that formed over a week ago. Settlement over the past several days has really helped strengthen the now deeply buried weak layers of surface hoar that formed well over a month ago. On average we’re finding about 200cm of snow at all our observation sites with shallower snow on the south aspects. Dudley and Tim were in the southern Bitterroot and were finding very similar snow conditions to what I found in the Rattlesnake Sunday.

Weather Forecast and Avalanche Outlook

A wave of energy and moisture will impact the area starting Monday producing widespread precipitation through Tuesday morning. Warm air will accompany this system aloft making the snow water ratios low so accumulation is expected to be low even at higher elevations. A high pressure ridge strengthens over the west coast Wednesday and broadens Thursday keeping conditions dry until it begins to flatten on Friday.

Expect avalanche conditions to remain the same or improve until the next significant change in weather.

The next advisory will be issued on January 28, 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

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!


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.