The avalanche danger for the west central Montana backcountry is Moderate on wind loaded slopes and low on all other slopes. The southern Bitterroot is Moderate in all terrain.
Good morning, this is Jeff Carty with the West Central Montana Avalanche Center’s avalanche advisory for February 11, 2020. Today’s advisory is sponsored by LB Snow. This danger rating does not apply to operating ski areas, expires at midnight tonight, and is the sole responsibility of the U.S. Forest Service.
Weather and Snowpack
It’s been quite a week. After record warm temps and winds on Saturday, February 1, the weather switched gears, and the area has been consistently snowed on for 6 days. Anyone who has been out in the past few days knows how good the riding is.
Since Tuesday, February 4, we’ve received up to 5.1 inches of snow water equivalent (SWE) and averaged 3.5 inches of SWE throughout the forecast area. This translates to more than 3 feet of new snow. We measured snow depths up to 110 inches in the Rattlesnake yesterday.
Despite arriving with strong winds, the bulk of the storm was relatively calm. Mostly light winds, with long calm stretches, moved much less snow than was anticipated, despite some strong gusts. Wind slab did not develop to the extent that we expected. Isolated, steep, high elevation terrain is where it is possible to trigger a wind slab avalanche. Cornices grew considerably and are a hazard as well.
Overall the storm snow has bonded surprisingly well. Mid storm density breaks that were showing some instabilities on the 7th have healed well. The February 1 crust has also bonded well and does not seem to be an issue. Storm slabs may be found in isolated spots, and overall, are unlikely to slide.
Loose snow avalanches or sluffs can be a problem in steep terrain, >38º. While mostly manageable they become more hazardous if they can push you into terrain traps.
The only place showing significant red flags in the forecast area is the southern Bitterroot around Lost Trail. On Saturday there was a natural avalanche, to ground, in the depth hoar that was plaguing us through January. Everywhere else in the forecast area has received enough snow for that layer to gain strength. The southern Bitterroot has received the least snow in the forecast area, and in thin spots, it is still possible to trigger a persistent slab avalanche in that area. It’s been 24 days since we’ve had a report of a slide on this layer, highlighting the unpredictability of this problem.
The Bottom Line
In most of the forecast area, the avalanche hazard is low, and it is unlikely to trigger an avalanche. Low hazard does not mean no hazard; do your due diligence. Dig a pit, test the snow, watch for red flags. Avoid steep wind loaded terrain near ridge tops. Give cornices a wide berth. Ski one at a time.
The southern Bitterroot requires more caution as the depth hoar is still active. Check snow depths throughout tours; shallow areas are more likely trigger points. Sticking to lower angle simple terrain is still the best approach to this problem.
Always carry your beacon, shovel, and probe.
As always, we welcome all public observations of avalanche conditions, please submit them here.
If you’d like to increase your avalanche knowledge and competence, check out our course offerings.
Ski and ride safe.