Good morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on, Monday, February 20 at 7:30 a.m. Pinhead Classic Telemark Festival, in partnership with the Friends of the Avalanche Center, sponsors today’s advisory. This advisory does not apply to operating ski areas.
Over the past 24 hours quiet weather has been in place over southwest Montana. This pattern should continue through much of today. Currently, mountain temperatures are ranging from the single digits to low teens and winds are blowing out of the WNW at 15-25 mph. Today, temperatures will climb into the twenties and winds will gradually increase out of the WNW blowing 25-35 mph. Skies will remain mostly clear through the morning, but an approaching front will produce increasing clouds by this evening. A warming trend will allow temperatures to rise to above seasonal averages by tomorrow.
The Bridger, Madison, and Gallatin Ranges, the Lionhead area near West Yellowstone, and the mountains around Cooke City:
The snowpack continues to show signs of weakness.
- Yesterday, skiers intentionally triggered one of the Titanic Chutes off Yellow Mountain near Big Sky. This slide broke 7-10 inches deep and propagated over 400 feet across.
- Other skiers in Beehive Basin observed a significant avalanche on a west-facing slope around 9000 ft.
- On Saturday night, Doug observed recent avalanche activity while involved with a search and rescue mission near Sacajawea in the Northern Bridger range. He and his rescue partners came upon debris from a large natural avalanche that originated in the bowls above Fairy Lake.
- A skier near Cooke City observed natural avalanche activity on east and north facing slopes (photo).
- The Bridger Bowl Ski Patrol triggered soft slab avalanches during control work yesterday (photo).
A weak interface between the old snow surface and new storm snow is the culprit for most of the activity (video). Any slope that has received a wind load or is steeper than 35 degrees will be the most susceptible to human triggered avalanches. Steep rollovers or areas where the snowpack is thinner, mainly around rock outcroppings or near thin scoured areas will be likely trigger points.
The widespread nature of the avalanche activity is a good reminder that storms of six inches or less are still capable of producing dangerous avalanches.
Although the snowpack has had a day to adjust it will remain reactive to the weight of a skier or rider. For this reason the avalanche danger is rated CONSIDERABLE on wind loaded slopes and slopes steeper than 35 degrees. Less steep, non wind loaded slopes have MODERATE avalanche danger.
Doug will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations, drop us a line at mtavalanche@gmail.com or call us at 587-6984.
NRCS Snowpack Summary Graphs
For the current state of our snowpack depth (about 70% of average on the Gallatin), check out these two graphs generated by NRCS (graph 1, graph 2).