Good morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Monday, March 28, at 7:00 AM. Today’s advisory is sponsored by Spark 1 and Javaman. This advisory does not apply to operating ski areas.
Overnight a fast but potent storm delivered a good shot of snow to the advisory area. At 5 a.m. the Bridger Range and mountains around West Yellowstone are recording 8-10 inches of new snow while the mountains around Big Sky and Cooke City are recording 5-6 inches. This morning temps range from the mid-teens to low 20s F and winds are blowing 5-15 mph out of W-NW. Today, skies will be partly to mostly cloudy and there is a chance for scattered mountain snow showers, but no real accumulation is expected. Highs today will warm into the mid-20s to low 30s F and winds will continue to blow 10-20 mph out of the W-NW. Another round of snow moves into the area tonight and tomorrow. The mountains should see 1-3 inches by tomorrow morning and potentially 6-8 inches by Wednesday morning.
Bridger Range Madison Range Gallatin Range
Lionhead area near West Yellowston Cooke City
March Madness continues. Over the past week the mountains have picked up 1.5 to 3 feet of new snow. In most cases the new snow has bonded well to a variety of old snow surfaces, which has helped limit avalanche activity. Yesterday, Doug and I rode in Tepee Basin in the southern Madison Range and found a mostly stable snowpack. We did observe one recent slab avalanche that broke on a wind loaded slope, but the slide was relatively small and stay confined to the new snow.
Today, wind slabs will be the main avalanche concern. Although winds are relatively calm this morning, they did blow hard out of the west-northwest during the storm. This likely created thick and dense wind slabs near the ridgelines. Watch for cracking and collapsing within the new snow and avoid steeper slopes where wind loading has taken place.
While wind loaded slopes will be the most problematic, non-wind loaded slopes have the potential to produce slides. Density changes within the new snow could produce slab avalanches in steeper terrain (photo). This type of instability is usually short lived, but could be an issue today. Also, weak layers buried deeper in the pack may be more reactive under the weight and stress of the new snow (photo). These deeper weak layers do not exist on ever slope so it’s worth digging a quick pit and doing a stability tests before committing to steeper slopes.
Additional Problem: Cornices
Large cornices have formed across the advisory area. These massive chunks of snow are now beginning to fail naturally and with human triggers. Yesterday, skiers up Flanders drainage in Hyalite observed a natural cornice fall that triggered a large slab avalanche on the slope below. On Saturday, a skier near Gardiner fell off a corniced ridge when he got too close to the edge and the cornice broke. This resulted in a large slab avalanche on the slope below (photo). Fortunately the skier escaped unharmed. Give these monsters a respectable distance both on the ridge above and the slope below.
Today, human triggered avalanches are likely on wind loaded slopes steeper than 35 degrees which have a CONSIDERABLE avalanche danger. All other slopes have a MODERATE avalanche danger.
Doug will issue the next advisory tomorrow morning by 7:30 a.m. If you have any snowpack or avalanche observations to share, drop us a line at mtavalanche@gmail.com or leave a message at 587-6984.
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