Good morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Advisory issued on Saturday, April 9, at 7:15 AM. Today’s advisory is sponsored by Spark 1 and Mountain Valley Motorsports of Cody. This advisory does not apply to operating ski areas.
Temperatures reached the low 60s F yesterday and are in the mid-30s to high 40s F this morning. Winds are out of the southwest at 10-20 mph with gusts around 30 mph along ridgelines. Today will be mostly sunny with wind out of the west at 15-25 mph and temperatures in the 50s F. A cold front will bring increased cloud cover this afternoon with cooler temperatures and a chance for showers this evening.
Bridger Range
Above freezing temperatures in the Bridger Range did not allow the snowpack to freeze for the second night in a row. Wet snow avalanches are likely today and large natural wet avalanches are possible. Avoid avalanche terrain and runout zones. Wet snow avalanches can run far and entrain a lot of snow. The avalanche danger is CONSIDERABLE.
Madison Range Gallatin Range Lionhead area near West Yellowstone Cooke City
In the mountains south of Bozeman overnight temperatures remained above freezing, and clear skies allowed only a slight freeze of the snow surface. Yesterday the Big Sky ski patrol triggered a couple deep wet avalanches in areas with a thin snowpack, and they reported a large cornice triggered slide on Cedar Mountain. The snow surface will thaw quickly today and unlock unstable wet snow below. Wet loose avalanches are likely and wet slab avalanches are possible.
Wet slab avalanches require three ingredients: A slab, buried weak snow, and liquid water moving through the snowpack. Recent heat has introduced liquid water from snowmelt. Depth hoar at the ground has not been active in months, but still exists on some slopes, and shallower buried weak layers exist on some slopes. The patchy distribution of weak snow means wet slabs are not a sure thing, but now is a likely time for them. Warm temperatures have weakened the snowpack and stability is being tested as water percolates through. Stability will decrease rapidly if precipitation falls as rain this afternoon.
Wet loose avalanches could gouge to deeper layers in the wet unconsolidated snowpack. These avalanches can grow large, and even smaller slides can sweep a skier over cliffs or into trees and other terrain traps. Deep wet slide debris was observed at low elevations in Emigrant gulch, which shows how large and dangerous these instabilities can be (photo, photo). Smaller wet loose avalanches observed at higher elevations are also powerful enough to cause harm (photo). The wet snow avalanche danger will start LOW this morning and quickly rise to CONSIDERABLE.
Cornices are large and can break farther back from the edge than expected. A cornice fall or wet loose avalanche could trigger a deeper avalanche. Give cornices a wide berth as you travel along ridgelines, and avoid slopes below them.
The dry snow avalanche danger is LOW. Dry avalanches are unlikely as the snowpack becomes wet on all aspects. High elevation and shady slopes still hold the possibility to trigger an avalanche in dry snow.
For more spring snow travel advice see the article I posted on our blog page, here.
Eric will issue the last advisory of the season 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.
EVENTS and AVALANCHE EDUCATION
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