February 17, 2012 Avalanche Advisory

On terrain that is 35 degrees and steeper there is MODERATE Avalanche Danger in the West Central Montana backcountry. Moderate danger means heightened avalanche conditions on specific terrain. On terrain that is 35 degrees and steeper with rock outcrops or cliffs, and/or wind-loaded, it’s possible to trigger an avalanche. Elsewhere in the forecast area there is LOW Avalanche Danger.

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for February 17, 2012.

Weather and Snowpack Analysis

It’s snowing this morning and snotels around the region indicate most areas have picked up 2 to 4 inches of snow overnight.  The last couple of days brought us a few inches around the region as well. This snow has come in cold and provided a nice shot of mid-winter “freshies”. The negative part of this scenario is the surface hoar layer from early February is now buried on many aspects under 8 to 12 inches of snow. Yesterday, at just under 8000 feet in the Rattlesnakes, I found buried surface hoar underneath 25cm (10 inches) of cold, loose snow. This top layer of snow is starting to form a slab on any sun-exposed slopes. On the colder, protected slopes it is sluffing easily when skied.  At lower elevations, where it is a bit warmer, it is sluffing impressively when triggered. This video, Tim took yesterday, is on a southerly aspect in the Rattlesnakes just under 7000 feet.   You can check out the debris from the videoed sluff in this photo.  Its ok Tim didn’t know exactly what day it was; he was supposed to be skiing, not working!

I also talked to a skier who got pushed around, rather forcibly, from a big sluff this week. This is something to keep in mind when skiing and riding near rocks, trees or anything that increases the consequences of getting “sluffed”.

Observer Matt Young had some weak to moderate results with stability tests on the buried surface hoar near Lolo Pass. Reports from near Lookout and Lost Trail Pass indicated a more stable snowpack. But, the report near Lost Trail noted concern with the buried surface hoar and predicted snow for the weekend. The Hoodoo Pass observers reported a mostly stable snowpack but noted weakness in the top 15 cm (6 inches).

Things are changing from our recent period of Low Avalanche Danger. The surface snow is starting to move a bit naturally and when triggered. And, there is more snow accumulating that can move.  Our concern right now is with the specific terrain mentioned above; don’t let an avalanche sneak up on you.

Weather Forecast and Avalanche Outlook

La Nina may tiptoe back into West Central Montana for President’s Day Weekend. Light snow is expected to last through this morning. A winter weather advisory has been issued that begins tonight and goes through Saturday night. The terrain along the Idaho border has the best chance for up to 7 inches of snow. Winds are not predicted to be very strong with this system, but the potential is there for some wind-loading on Saturday. The avalanche danger will escalate with more snow. I would expect there to be more areas with Moderate Avalanche Danger than those mentioned above and those areas will become touchier.

I will issue the next advisory on President’s Day.

Ski and ride safe and have a great weekend.

If you get out and see avalanche activity or want to send us quick snow observations please use our public observations form on the home page missoulaavalanche.org or write us at info@missoulaavalanche.org with any observations or questions.