Feb 25, 2014 @ 6:21 am

Avalanche Advisory for February 25, 2014

The avalanche danger is CONSIDERABLE on wind loaded terrain above 5000 feet that is steeper than 35 degrees.

Natural avalanches are possible, human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding and conservative decision making is essential on leeward terrain.

On all other terrain in the west central Montana backcountry, the avalanche danger is MODERATE.  

Heightened avalanche conditions can be found on steeper terrain in areas where deeply buried weak faceted snow exists. Snow and terrain must be evaluated carefully to identify these areas of concern.

Good morning!  This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday February 25.  This information is the responsibility of the Forest Service and does not apply to operating ski areas.  The danger rating expires at midnight tonight.


Weather and Snowpack

A major winter storm impacted western Montana during the past few days bringing February snow totals in the valleys to near record levels.  SNOTEL data indicates that many valley locations picked up significantly more snow than many mountain locations.  The mountains indeed have received plenty of new snow and conditions appear to be surprisingly stable.

Mountain temperatures this morning are in the teens and winds are light from the north and northeast.

SNOTEL stations report about .50 inches of snow water equivalent (SWE) or over 6 inches new snow in the past 12 hours.

We’ve received no reports of avalanche activity, natural or otherwise, during the past 4 days.  The Snowbowl Ski Patrol did initiate several soft slabs using explosives during morning avalanche control Monday. This involved mostly the newest snowfall from the previous 24 hours.  I would expect they are finding similar conditions this morning.

In both the Lolo Pass and Rattlesnake backcountry avalanche specialists were pleasantly surprised at how much the stability has improved. The overall snowpack appears to have adjusted well to the new load. No cracking or collapse noise was experienced in either area and stability test scores were high with no propagation.

During a Level 1 class in the Rattlesnake this past weekend, instructors reported that stability test scores increased through the weekend.  The now deeply buried facet layer still fails cleanly in some pits, but it takes a lot of force to get it to fail and it does not propagate like it did last week.  You can view the snow profiles for the Rattlesnake and Lolo Pass backcountry on our 2013/14 Snow Profiles page.

The primary avalanche problem today is wind slab development on lee terrain steeper than 35 degrees.  Last week, the wind was brutal and created sensitive slabs on a variety of lee terrain. While these slabs have had a few days to heal, they now have a lot more weight on them and can still be triggered if you hit the right spot.  Cross loaded pockets and terrain convexity are places where one of these could pull out.

A secondary concern is storm snow slabs on terrain steeper than 35 degrees.  Temperatures have been pretty cool during this storm so the newest snow hasn’t yet formed a slab in most areas.  It will as settlement occurs especially once temperatures rise again.

Of course with all the fresh powder out there, it will be easy to get a good size loose snow avalanche to slough off the steepest terrain which could add enough weight to step down to deeper weaknesses.


Weather and Avalanche Forecast

The recent surge of moisture is expected to diminish today as a short lived high pressure system builds over the area.  Weather models indicate that another air mass and snow event will impact the area Thursday possibly lasting through the weekend.

I expect the avalanche danger to remain similar but will increase rapidly to HIGH on leeward terrain if the wind starts moving snow around.  Warmer conditions will also increase the avalanche danger but that is not in the near term weather forecast.

Conditions are about as good as it gets.  We are in the cautionary area where stability appears to be pretty good but there’s still enough concern about some of the steeper lee terrain to keep your situational awareness operating at a high level.  Don’t take chances that may get you or someone else in trouble.  We’re seeing far to many You Tube videos of skiers and snowmobilers on steep terrain together.  There have been some unfortunate accidents recently where more than 1 person was caught.

They only way you or your partners will have a chance at surviving a burial is to make certain only one person at a time is exposed.

Have a great time but play it safe out there!  I will issue the next avalanche advisory this Friday, February 28.



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.