Vail & Summit County
SnowpackSean Lynn · Jan 30, 2017 · Vail & Summit County
Weather
A significant warming trend over the previous 4 days was observed, with increasing levels of sun exposure. Wind had been high all day over the divide but valley of avalanche was wind-protected. Estimated gusts in the high 40mph range measured by effects on people hiking the divide.
Snowpack
Elevation of slightly over 11800 feet above treeline. Hardened wind slab was observerd in the affected area over a faceted sun crust. Most windward areas were highly wind scoured with little remaining snow. Most leeward slopes were hardpacked wind slabs. The exception to this was more easternly facing slopes which contained approximately 4-6 inches of cohesive but lighter sun effected-to-faceted deposited snow. Variation between the two conditions was variable.
Two skiers as part of a five skier avalanche education course purposefully set out to test reactivity and propagation of a low-angle (22 deg), SW facing, wind loaded slope above treeline. The slope runout was of significantly lower angle than the main slope and was estimated to not support full release. Skiers traversed high on the slope near the start zone and were able to immediately trigger a hard slab release and propagation of nearly the entire (small) slope. As predicted, the slope released, but the snowpack had nowhere to run. Area of weakness was wind slab over a faceted sun crust - both noted in previous CAIC forecasts as well as previous three days of team physical observations.
Collapsed area was 100 x 30 m, and 10 cm deep on Old/New interface. Slope angles were 22 to 26 degrees.
Two skiers as part of a five skier avalanche education course purposefully set out to test reactivity and propagation of a low-angle (22 deg), SW facing, wind loaded slope above treeline. The slope runout was of significantly lower angle than the main slope and was estimated to not support full release. Skiers traversed high on the slope near the start zone and were able to immediately trigger a hard slab release and propagation of nearly the entire (small) slope. As predicted, the slope released, but the snowpack had nowhere to run. Area of weakness was wind slab over a faceted sun crust - both noted in previous CAIC forecasts as well as previous three days of team physical observations.
Collapsed area was 100 x 30 m, and 10 cm deep on Old/New interface. Slope angles were 22 to 26 degrees.