Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Tuesday, February 21 at 7:30 a.m. The Yellowstone Club Community Foundation, in partnership with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.
At 6 a.m. seven to nine inches of new snow has fallen throughout southwest Montana. A moist Pacific storm is driving through on a northwest flow. Mountain temperatures are in the teens and ridgetop winds are blowing west to northwest at 25-35 mph. The storm is expected to pick up later this morning and last through Wednesday. Today winds will pick up to 30-40 mph and more snow will fall. By morning I expect 10-12 inches in the mountains.
The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone and the mountains around Cooke City:
If you enter avalanche terrain today you will likely trigger an avalanche. Today is not a day to trifle with the snowpack. It’s ornery and getting more dangerous as more snow falls and wind blows.
Last week we formed a weak layer at the surface that quickly became unstable once it was buried. This layer of small-grained facets is buried about a foot deep and is found on all aspects of the compass throughout our entire advisory area. In the last two days it was propagating fractures and avalanching. Our current snow storm is rapidly loading slopes increasing stress on this layer. On slopes with thin snow cover, like in the Bridger and northern Madison Range, I expect avalanches to step down to the ground on large, sugary grains of depth hoar. Avalanche activity is Mother Nature’s warning sign that slopes are unstable. Activity includes:
- Outside of Cooke City on Saturday, Mark triggered a slide on this layer of near-surface facets. Yesterday, a snowboarder and his friends were able to trigger pockets on every run they took near Fisher Peak. The winds were ripping and loading slopes during the day and have not abated.
- I investigated an avalanche in Beehive Basin that ran 500 feet wide on Sunday on this layer. It broke to the ground in spots too. (photo 1, photo 2, video of crown)
- Skiers also triggered a large slide on Yellow Mountain on Sunday.
- Yesterday, a skier in Hyalite triggered two small pockets on steep slopes near Divide Peak (photo) when the snow broke on these facets.
- I saw debris from natural slides in the Bridger Range early Sunday morning near Sacajewea and Hardscabble Peak.
For today, the avalanche danger is rated HIGH on wind-loaded slopes steeper than 35 degrees and CONSIDERABLE on all other slopes. Instability is widespread. If the storm continues the avalanche danger will rise further.
I 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.