Good morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Saturday, December 8 at 7:30 a.m. Today’s advisory is sponsored by Montana Ale Works in partnership with the Friends of the Avalanche Center. Bridger Bowl is now open and uphill travel within its boundaries is no longer permitted.
Since yesterday, the mountains near Cooke City received 10 inches of snow, near Big Sky 4-6 inches of snow, and 2-3 inches most other places. This morning winds were averaging 20-30 mph from the W and NW with gusts of 40-60 mph. Temperatures were in the single digits to low teens F. Today, another 1-2 inches should fall and temperatures should bottom out at 0 degrees F before warming back up a few degrees. Fortunately winds should ease by afternoon and blow 10-20 mph from the NW. Tonight through Sunday should be dry with more snow coming Sunday night.
The mountains near Cooke City received significant snow for nine of the last 10 days (about 6 inches of SWE). Fresh wind slabs are the primary avalanche problem; however, avalanches could easily break deeper in the snowpack. The snowpack in the Cooke City area is generally strong, but everything has its breaking point. With about 20 inches of new snow in the last 48 hours and strong winds, avalanches are likely on wind loaded slopes steeper than 35 degrees where the avalanche danger is rated HIGH. Other slopes have a CONSIDERABLE avalanche danger
Bridger Range Madison Range Gallatin Range
Lionhead area near West Yellowstone
New snow and strong winds are a good combination for avalanches. Yesterday, skiers in Frazier Basin in the Northern Bridger Range found reactive snow near ridgetops and were able to ski cut a 6-8 inch wind slab. The Bridger Bowl Ski Patrol reported similar conditions during control work. Additionally, 2 separate groups of ice climbers triggered 8-10 inch wind slabs in Hyalite Canyon in a gully appropriated named Avalanche Gulch. Fresh wind slabs are the primary avalanche problem today.
A secondary problem is faceted snow near the ground. Yesterday the Big Sky Ski Patrol triggered an avalanche 1-3 feet deep in steep, E facing, wind loaded terrain near 9800 feet. They also noted a pocket of strong stable snow just under a section of this avalanche path as an indication of the variability. On Thursday, skiers in the Southern Madison Range observed a natural avalanche that likely broke 2-3 feet deep on facets near the ground. It occurred near 9500ft on a NE aspect (photo). Some slopes have weak, faceted snow near the ground while many others do not. To find these stable slopes, dig a snowpit to the ground and also choose ones facing the southern half of the compass with a fairly deep snowpack, lacking wind-blown snow.
Lastly, I found a buried layer of surface hoar in the Taylor Fork area of the Southern Madison Range on Wednesday (photo, video). We have limited data on the distribution of this weak layer but suspect it may exist near Cabin Creek, Teepee Basin and Lionhead. This layer is scary because it exists in isolated pockets on slopes sheltered from the wind, exactly the slopes where I would expect to find stable snow.
For today, the avalanche danger is rated CONSIDERABLE on all wind loaded terrain. On slopes without a wind load, the avalanche danger is rated MODERATE.
Eric 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.
Snowmobiler Introduction to Avalanches with Field Course in Billings at Hi-Tech Motor Sports on December 12 and 13, 6-9 p.m. and the field course on January 20 in Cooke City. Sign up for this class HERE
Snowmobiler Introduction to Avalanches with Field Course in West Yellowstone on December 20 and 21. Sign up for this class HERE.
FREE 1 hour lectures:
December 12, REI in Bozeman, 6:30 p.m.