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Glide Cracks and Rain on Snow

Location Name: 
Roadbank, Above Box Canyon Dam
Region: 
Mt. Shasta
Date and time of avalanche (best estimate if unknown): 
Sun, 01/08/2017 - 7:00pm
Observation made by: 
Forecaster
Red Flags:
Recent avalanche activity
Recent loading by new snow, wind, or rain

Location Map

United States
41° 16' 37.6644" N, 122° 19' 46.7472" W
See map: Google Maps
US

Avalanche Observations

Details

Glide cracks were observed on a north facing slope at 3240ft. The glide cracks pictured are both on the same slope just above Box Canyon Dam.  The photos were taken at 11am, and the glide cracks had to have occurred between 1am-11am this morning. A glide crack/ glide avalanche is the release of the entire snow cover as a result of gliding over the ground.  

2 inches of rain fell on a dry snowpack up to 7500ft today.  Evidence of this dramatic event was obvious in below treeline terrain observed today on a drive to Castle Lake and a drive to Bunny Flat.  Rain runnels were widespread (see photo).  The height of the snowpack decreased by 7 inches in some areas below 7500ft due to the rain on snow event today.

Characteristics

Avalanche Type: 
Wet
Trigger type: 
Natural
Slope: 
35degrees
Aspect: 
North
Elevation: 
3 240ft.
Terrain: 
Below Treeline
Weak Layer: 
Other - explain below
Bed Surface: 
Ground
Crown Height: 
Less than 1 ft
Avalanche Width: 
50ft.
Avalanche Length: 
10ft.
Number of similar avalanches: 
1

Weather Observations

Details

The 7500ft freezing levels forecasted for today were veryfied by local backcountry skiers and by our remote weather stations.  Significant snowfall has occurred above 9000ft, but exact snow totals for upper elevations are unknown at this time.

Statistics

Cloud Cover: 
100% of the sky covered by clouds
Blowing Snow: 
Yes
Precipitation: 
Mixed rain and snow
Accumulation rate: 
Greater than 1 in. per hour
Air temperature: 
Above Freezing
Air temperature trend: 
Cooling
Wind Speed: 
Moderate
Wind Direction: 
Southwest