Feb 5, 2013 @ 6:56 am

February 5, 2013 Avalanche Advisory

There is MODERATE avalanche danger in the mountains of west central Montana.  Natural avalanches are unlikely, human triggered avalanches are possible.  Heightened avalanche conditions exist on some terrain features such as recently wind loaded upper elevation slopes steeper than 35 degrees and in areas where facets formed on the snow surface during the Martin Luther King holiday.

Good morning!  This is Steve Karkanen at the West Central Montana Avalanche Center with backcountry avalanche safety information for Tuesday February 5, 2013.


Weather and Snowpack

Advisory area SNOTEL sites recorded temperatures into the high thirties on Saturday and Sunday then cooled back into the mid twenties on Monday.  Most sites have received a trace of precipitation by this morning and temperatures are in the twenties.

Last weeks storm snow has settled and bonded to the old snow surface during the past few days.  Warm then cold temperatures locked up all but the more sheltered northerly aspects. We’re finding a mostly stable snowpack with wind slabs being the primary avalanche problem above 8000 feet.  West to northwest winds have been relentless and moved a lot of snow during and after the last storm.  These hard slabs are stubborn but can do a lot of damage if you happen to trigger one.    

A secondary concern is a now deeply buried facet layer that continues to gain strength but fails cleanly in stability tests when enough force is applied.  This is not a widespread problem and the spotty/random nature of these buried facets makes it difficult to predict where they may be an issue. The only way to know if a slope has these little surprises is to dig down and look for them.

Last Thursday’s rime event that left a thin ice crust now about 6 inches down appears to be breaking down and is not producing failures in stability tests.

In places where wind scouring is keeping the snowpack thin, there is weak, faceted snow at the ground.  These places tend to be on more west – southwest facing slopes and it’s a good idea to keep them in mind.  These thin pockets have the weakest structure of any snow and are the most sensitive to triggers.


Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting light to moderate mountain snowfall through Thursday.  Six to nine inches of snow is expected along with an increase in westerly winds above 6000 feet.  The avalanche danger is expected to remain MODERATE.  Be wary of wind slabs during periods of high wind and new snow.

Although we are again trending toward mostly stable conditions, there are enough land mines out there that require good situational awareness and safe habits.  Just because we’re skiing and riding on steep terrain doesn’t mean we can’t trigger an avalanche.  Only expose 1 person at a time, spread out when traveling uphill and evaluate each slope before committing.

I will post the next advisory on Friday, February 8.

We’ve been receiving excellent reports from some of you.  These are very helpful to us.  If you get out we appreciate hearing about the snow stability conditions in the area you visit. Drop us a line at [email protected] and tell us what you see or post your observations on our public observations page.


Avalanche Awareness Program in Hamilton Wednesday 7pm

Dudley Improta will present an avalanche awareness program for the Bitterroot Ridgerunners Snowmobile Club and Ravalli County Search and Rescue this Wednesday, Feb. 6,  at 7pm in the Ravalli County Search and Rescue Building, 2029 N. First St in Hamilton.  The public is welcome and there is no fee.


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.