Good morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast issued on Thursday, February 21th at 7:00 a.m. Today’s forecast is sponsored Cooke City Super 8/Bearclaw Bob’s and Gallatin County Search and Rescue. This forecast does not apply to operating ski areas.
The Bridger Bowl Cloud delivered yesterday, producing 21” of very light snow (2.5% density) since early yesterday morning. A trace to 2” fell elsewhere. Temperatures are in the single digits above and below 0F this morning. Winds were 10-20 mph out of the northwest to northeast yesterday, and have diminished overnight. Winds will remain light and generally northerly today. Temperatures will rise into the teens F and flurries will bring a trace of new snow.
Close to two feet of snow fell on high elevation slopes in the Bridger Range yesterday. During the snowfall, soft slab avalanches were easily triggered and ran long distances. Large avalanches can be triggered within the new snow today. The most sensitive conditions will be found where the new snow has been stiffened by wind. Pay close attention to the snow surface texture to identify these areas. With this much new snow, large loose snow avalanches (sluffs) are a significant hazard on slopes that haven’t been wind affected. On wind-loaded slopes, human triggered avalanches are likely and the avalanche danger is rated CONSIDERABLE. On all other slopes, the avalanche danger is MODERATE.
In the southern ranges, the primary concern is weak snow at the base of the snowpack. While avalanches on these weak layers are becoming less likely, they are still a very real concern. Monday’s large avalanche on Lionhead Ridge that broke 6 feet deep is a good reminder of the how big and dangerous these slides can be (video, details and photos). Assessing stability on deep weak layers is difficult. Avoidance is really the best strategy for dealing with them. If you do get into steeper terrain, stack the deck in your favor by using good travel practices to minimize the consequences of a slide: only expose one person at a time and watch your partners from a safe spot. Remember that tracks on a slope don’t mean it’s stable, particularly with these deep instabilities. The 1st rider or the 15th could trigger a slide. The avalanche danger today is MODERATE.
Wind-loading has created two overlapping concerns: one shallow, one deep. Recently wind-loaded slopes can avalanche 1-2 feet deep. An avalanche that caught and partially buried a skier outside Cooke City on Tuesday provides a perfect example of this concern (photo, details). A less widespread, but even more worrisome concern is avalanches breaking on slopes that have a heavy wind-load sitting above weak snow deep in the snowpack. We saw a number of these slides last weekend: on Buck Ridge, in McAtee Basin, and on Crown Butte (photo, video, video). Avoiding slopes with large cornices above them or thick pillows of hard drifted snow sitting next to scoured ridgelines is the best way to avoid triggered one of these large slides.
Whether the wind-load is recent or weeks old, wind-loaded slopes have a MODERATE avalanche danger. The avalanches danger is LOW on all other slopes.
If you get out and have any avalanche or snowpack observations to share, contact us via our website, email (firstname.lastname@example.org), phone (406-587-6984), or Instagram (#gnfacobs).
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
February 22 and 23, Women’s Companion Rescue Clinic, 6-8 p.m. Friday at REI, 10-4 Saturday in the field. More Info and Register.
March 1, 2 and 3, Bozeman Split Fest, More info at www.bozemansplitfest.com.
February 23, 1-hr Avalanche Awareness for Snowmobilers, 7-8 p.m. Holiday Inn West Yellowstone.
Every Friday and Saturday, Rescue Training and Snowpack Update. Friday 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.
On Tuesday, a backcountry skier ascending a trail near Telluride, Colorado was buried and killed by an avalanche triggered by a rider descending above him. Preliminary details and photographs here.