Avalanche Warning for February 18, 2014

A BACKCOUNTRY AVALANCHE WARNING is in effect for mountain locations above 5000 feet in west central Montana.

This includes the Bitterroot mountains from Lost Trail Pass to Hoodoo Pass, the Rattlesnake mountains north of Missoula and the southern Swan and Mission Mountains on Lolo National Forest Lands near Seeley Lake, MT.

The avalanche danger is HIGH. Very dangerous avalanche conditions exist.  Natural avalanches are likely, human triggered avalanches are very likely.  Travel in avalanche terrain is not recommended.  Any open terrain steeper than 30 degrees especially recently wind loaded terrain is dangerous.  Avoid avalanche paths and their run out zones.

Good morning!  This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday, February 18.  This information is the responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight. The avalanche warning will either be extended or allowed to expire Wednesday morning.

 

Weather and Snowpack

Heavy new snowfall and high wind speeds are rapidly increasing the stress on weak layers and old storm snow interfaces in many areas.

The Bitterroot Range is getting hammered, especially the northern half of the range from Lolo Pass to Hoodoo Pass.  The Hoodoo SNOTEL site reports nearly 2 inches of snow water equivalent (SWE) in the past 24 hours and about an inch of SWE at Lolo Pass. Other SNOTEL sites throughout the region report just over a half inch of SWE.  Keep in mind that much of the snow came in horizontal so the measured amounts may be skewed.

Wind speeds peaked at 60 mph at Point Six and 54 mph at Deer Mountain near Darby.  This morning the winds are gusting to 45 from the west at Point Six and SW gusting to 24 mph at Deer Mountain. Mountain temperatures are in the mid 20’s.

We received a report from the Ward Mountain area of high winds and heavy snowfall causing near blizzard conditions. 6-8″ of new snow accumulated here with perhaps as much as a foot at some of the higher elevations. Similar conditions were experienced near Lolo Pass and in the Rattlesnake yesterday.

The primary avalanche problem today is wind slab formation on any lee terrain steeper than 30 degrees.  These will be very sensitive and found in places further down the slope than expected.

A secondary problem is the storm snow adding enough weight to make the deeper weak layers reactive again. Facets that formed during the late January dry spell are still present and are now close to the failure point. Stability testing in the Rattlesnake and Lolo Pass areas were bringing out clean energetic failures about a meter deep into the pack. You can view the profiles here.

The upper storm snow interfaces were showing signs of strengthening however the newest storm snow was failing readily and on its own on steeper slopes.  A loose snow avalanche or sluff may be manageable, but it may also be enough added weight to step down to the deeper weakness to produce an unsurvivable hard slab avalanche.

We received several reports of human triggered avalanches over the weekend.  One of these resulted in a near full burial and loss of equipment. Thankfully, there were no injuries in this incident and the individual sent us a great report which is posted on our public observations page.

This incident is scary in that the individuals have excellent skills and experience but triggered a slab that failed much deeper than expected.  We have not visited the site but are confident this failure happened on the faceted layer that formed in late January.  We are all thankful no one was injured in this incident.

 

Weather and Avalanche Forecast

Winter weather advisories have been posted by the Missoula Office of the National Weather Service. They are forecasting continued heavy snowfall and high winds for the next few days. Some locations favored by orographic lifting may receive over 20 inches over the course of the next couple of days. Wind speeds will be in the 50mph range at ridge tops.

The avalanche danger will remain HIGH at least until the next break in weather and the snow has the chance to adjust to this new load.

This is a tricky and dangerous snowpack right now.  The above close call is a good illustration of what can happen with this now deeply buried weak layer.  We’re not finding it everywhere we dig, but when we do, it produces consistently clean failures.

Until the storm snow settles, avoid any steep open terrain, be aware of your location in relation to avalanche run out areas and never expose more than 1 person at a time to anything with potential to slide.  Make sure all your gear and your partners gear is in good working order.

 

Education

There is still room in the Bitterroot Level 1 class that starts next week.  This will be an excellent class with two field days in the Lost Trail backcountry. You need to register TODAY!

I will issue the next scheduled advisory this Friday, February 21.