Natural avalanche Highway 89 Highway Patrol Chute

Location Name: 
Highway 89 Highway Patrol Chute
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of avalanche (best estimate if unknown): 
Sun, 03/20/2011 - 11:50
Location Map: 
United States
39° 11' 15.8208" N, 120° 11' 23.2296" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Trigger type: 
Natural
Aspect: 
West
Weak Layer: 
Storm Snow
Avalanche Width: 
50ft.
Terrain: 
Near Treeline
Elevation: 
7 200ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
1 000ft.
More detailed information about the avalanche: 

This avalanche released naturally out of a cross loaded W aspect gully in near treeline terrain with directly wind loaded N-NW aspect wall on the south side of the gully. Visibility was too poor to see the crown from road level so the above info regarding bed surface, weak layer, avalanche width, and avalanche length are estimated based on knowledge of the avalanche path and other snowpack observations from yesterday and today. Slope angle greater than 35 degrees. Crown height is unknown. Debris measured 8 feet deep at centerline on the highway. This known avalanche path rarely receives explosive control work and had not been controlled yet this season. No vehicles were caught.

Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Warming
Wind Direction: 
Southwest
Accumulation rate: 
Greater than 1 in. per hour
More detailed information about the weather: 

Nearby remote sensor at 6,800' (Alpine Meadows base area) reported 12 inches of new snow in this area between 7am and the time that the avalanche occurred. 21 inches of new snow at this sensor in the past 24 hours.