February 1, 2010 Avalanche Advisory

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for February 1, 2010.

Current Avalanche Danger
On slopes steeper than 35 degrees and on all aspects at elevations above 5000 feet, the avalanche danger is MODERATE. Natural avalanches are unlikely, human-triggered avalanches are possible.
In the Rattlesnake Mountains at elevations above 6000 feet on slopes steeper than 35 degrees the avalanche danger is MODERATE with pockets of CONSIDERABLE. On steep slopes with North and West Aspects in the Rattlesnakes human-triggered avalanches are probable.
On other terrain within the advisory area the avalanche danger is LOW.

Weather and Snowpack Analysis
The MODERATE hazard rating indicates there is the possibility of a slide on certain terrain features. Any steep areas where the snow is shallow from wind disbursement are suspect. The Rattlesnake Mountains received up to 6 inches of snow with over a half an inch of snow water. This heavy snow is sitting on top of surface hoar formed from Wednesday and Thursday night. Suspect areas in the Rattlesnakes with CONSIDERABLE hazard include steep slopes with Northeast, North, Northwest and West aspects.

We did get the snow to fail yesterday but it took a lot of force. We had some moderate failures on the early January surface hoar and the depth hoar from early December. Our tests are not showing clean fast shears with lots of energy but they are failing at some point during the test. Surface hoar formed on Wednesday and Thursday last week and the area received 3 to 6 inches of snow yesterday and last night. Snotel sites indicate the Rattlesnake Mountains received up to 7 inches which has settled to 6 inches.

Friday was sunny and warm at elevation. The sun destroyed the surface hoar on South and East slopes and caused some surface movement in many places Friday afternoon; a reminder that the snow will move when subjected to rapid warming. We observed plenty of surface sluffing yesterday on steep slopes while skiing. This was the new snow on top of the aforementioned surface hoar from the end of last week. The new snow from Sunday and Sunday night is dense and snotel sites in the area indicate it is settling rapidly, but, take into consideration the possibility of a human-triggered slide before jumping into steep slopes above 5000 feet.
The following You Tube video was shot while the new snow was coming in, it will give you an idea of the layers that are present. We got 6 to 7 inches of dense snow in the Rattlesnakes after the video was shot. That new heavy snow is sitting on the surface hoar shown in the video.

Weather Forecast and Avalanche Outlook
Light snow continues to be a possibility during the next several days over high terrain. The snow is predicted to remain light and accumulate slowly. This scenario bodes well for avalanche stability; however if the winds do pick up snow could produce loading on lee sides. Keep this in mind as well as the other possibilities of weakness mention in the Current Avalanche Danger.

The next advisory will be posted on 2/5/10.

Missoulaavalanche.org is currently running a survey until 2/15/10 to improve avalanche advisories and education. To access the survey visit www.surveymonkey.com/s/PC6Z5BH . Please take a few minutes to help us out. At the end you can enter a drawing to win a BCA Tracker Beacon, a Voile Avalanche Shovel or a missoulaavalanche.org t-shirt.

If the Beacon Park is not set up at Snow Bowl ski are you can get the control box from the summit patrol shack. The Snow Bowl Patrol will retrieve it when they sweep. For all Beacon Park information go to mslaavalanche2.wpengine.com/beacon_training.php .

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).