February 12, 2013 Avalanche Advisory
The avalanche danger in the west central Montana backcountry is MODERATE. It is possible to trigger avalanches on slopes above 7000 feet and steeper than 35 degrees. Site-specific avalanche problems exist, including wind slabs on high exposed ridges, weaknesses on shallow wind-scoured slopes and large, loose snow sluffs from the weekend’s snow storms.
Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday, February 12, 2013.
Weather and Snowpack Analysis
This morning mountain temperatures are in the 20’s with light winds out of the north and northwest. Prevailing winds are expected to change to west and southwest this afternoon bringing snow to the higher elevations.
Some welcome snow arrived this weekend. I had a level 1 class in the backcountry near Lost Trail Pass Saturday and Sunday. We woke up to 6 inches of fresh, cold snow on Sunday morning and had another 4 inches fall during the day. This new snow near Lost Trail is sitting on a weak surface; check out this Lost Trail snow profile from Saturday. Lookout Pass to the Rattlesnakes received 3-5 inches of snow. Lolo Pass got about 5 inches; Steve and Tim were up the Brushy Fork of Lolo Creek yesterday and noted about 5-6 inches of new snow.
The snow came in cold and light near Lost Trail; while not increasing the load significantly, this light snow is readily available for wind transport. The last few days winds gusted above 15 mph and large cornice development across the region indicates the winds have been moving snow. Pay attention to hard wind-packed snow or snow that feels hollow or stiff; these areas could harbor hard wind slabs.
Older weak layers in the snowpack appear to be bonding. Steve and Tim noted stable snow in the Brushy Fork; with a 270 cm snowpack. Generally, where the snow is deeper, older weaknesses are strengthening. Suspect spots for trigger points are wind-scoured areas or where the higher elevation snow is shallow.
Loose snow sluffs from the weekend’s storm snow were observed from Wisherd Ridge to Lost Trail. Some of these were natural and some were triggered; all on very steep terrain. On the steeps above 7000 feet be aware of the potential for a large sluff to knock you over and carry you into a bad place (trees, rocks, cliffs, gullies).
Weather Forecast and Avalanche Outlook
The potential for snow looks good for this afternoon through Thursday morning. Forecasts call for up to 8 inches of warmer, heavier snow at higher elevations accompanied by winds exceeding 25mph.
The potential for warmer, heavier snow on top of colder, lighter snow exists. With the wind-loading it’s a no-brainer; I expect the avalanche danger to increase after the arrival of this system.
I will issue the next advisory Friday, February 15.
As of this morning, there is still a couple of spots left in our Level 1 Class at Lost Trail beginning March 1.