February 19, 2010 Avalanche Advisory
Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for February 19, 2010.
Current Avalanche Danger
On slopes above 6000 feet and steeper than 35 degrees there is a CONSIDERABLE avalanche hazard. Natural avalanches are possible, human triggered avalanches are probable. On other steep terrain above 5000 feet there is a MODERATE avalanche hazard. Human triggered avalanches are possible. On remaining terrain within the advisory area the avalanche hazard is LOW.
Weather and Snowpack Analysis
The slab I reported about Monday is still with us. I toured the Rattlesnakes today and had unstable results with my stability tests on four different aspects. Tim traveled into the Brushy Fork area of Lolo Creek and found the same conditions. We received a report from the Downing Mountain Lodge near Hamilton that the snow was failing easily on the buried surface hoar as well. Since Monday morning the region received a bit more snow and the slab is anywhere from 12 inches to 20 inches thick across the area. We had surface hoar develop across the region in late January and early February. We haven’t gained much snow since then; but what we have gained is sitting on top of this well preserved surface hoar. This layer should be scrutinized for the foreseeable future; particularly above 6000 feet and on slopes with Northerly aspects.
Tim was able to safely ski cut an avalanche in the Brushy Fork that propagated 200 feet across the slope and ran 150 feet into a terrain trap.
I have posted photos of the surface hoar layer in the Rattlesnakes and the slab avalanche in the Brushy Fork on our photo gallery. You can find them at the end of the 2010 season folder.
Weather Forecast and Avalanche Outlook
A Northerly flow is expected to continue through the weekend with slight cooling and modest precipitation, if any. I would look for conditions to stay the same for a few days, particularly on Northern exposures where the snow will remain cold at elevation. For the time being, approach all steep slopes at elevation with suspicion.
Notes from President’s day Weekend
This past weekend I know of two well seasoned, cagey backcountry skiers who separately triggered avalanches, were caught, and fortunately came through unscathed. The story is all too familiar for one of them. Obvious clues were there, the settling, the cracking and yet with the lure of a virgin powder run somehow things looked safe. None of us are impervious to the “human factor”. We received a comment that someone pre-judged conditions to be stable when the Feb. 12 advisory rated the hazard as MODERATE. First of all, a MODERATE rating does not say conditions are stable; it says human triggered avalanches are possible and there are dangerous conditions in certain terrain features. Even a LOW rating indicates “mostly” safe conditions. And due to the capricious element of snow and weather, hazard ratings must expire by midnight of the day issued. The information contained can provide valuable information for further investigation however.
Do not forego safe travel habits because of perceived stability.
Secondly, do not put all your eggs in one basket, constantly seek information. Do not rely on any one thing; whether that is a snow pit, lack of obvious clues or an avalanche advisory. Endeavor to put the whole picture together.
I will be instructing an avalanche awareness class, along with Lost Trail Ski Patrol members and instructors from missoulaavalanche.org, in Hamilton and Lost Trail Pass this weekend. There is an evening session tonight at 6pm in Conference Room B at Marcus Daly Hospital and a field session Saturday at Lost Trail Pass Ski Area. The class is co-sponsored with the Lost Trail Pass Ski Patrol. You can find more info on the education link on missoulaavalanche.org. $20 donation.
Steve will post the next advisory on February 22.
If you get out and see avalanche activity or want to send us quick snow observations, send us a note at [email protected] or call us at 406-530-9766 (530-9SNO).