Northwest Avalanche Center

Observation: Public

All Observations

Observation Details

Name:
NH-S/RC
Observation Date:
December 28, 2020
Submitted:
December 28, 2020
Zone or Region:
Stevens Pass
Activity:
Skiing/Snowboarding
Location:
Arrowhead

Observed Avalanches

Did you observe any avalanches? 
Yes
Avalanche Type:
Hard Slab
Size:
Size 2: Could bury, injure, or kill a person
Elevation:
5300'
Aspect:
W
Comments:
Large natural avalanche on northern side of Arrowhead leftover from 12/21 rain event. 40-degree slope below rock band. HS-N-R2-D2
Photo:

Signs of Unstable Snow

None reported

Observations

HS: 185cm 5400' west. 12/25-26 HST was 10-18 cm depending on exposure to wind.

Above 5600' melt-freeze crusts are forming from inversion and sun. Rime around 6000'. Inversion conditions have led to widespread near-surface faceting below 5000' and widespread surface hoar in wind and sun-sheltered locations above 5000'. Wind-deposited snow was not reactive and no underfooot instability was noted today.

Quick pit (5400', west aspect) revealed 10cm of new snow over the solstice rain crust, rounding facets beneath, another melt-freeze crust underlain by rounding grains, then several layers of decomposing crust and rounds/rounding facets. 12/9 crust indicated by Voile strap at 80cm in photo. CT12 Q2 on 1mm facets 40cm down, but this layer was bridged by several crusts above it when not isolated as a block.

Take-away: The solstice crust (and the four other crusts) seem to be bridging the near treeline snowpack well at this location despite weak snow throughout the profile.

Prospectus: The incoming Tuesday night-Wednesday storm will fall on a variety of snow surfaces (faceting 12/25-26 snow over 12/21 crust low; surface hoar mid-slope, melt-freeze crusts on high, sun-exposed slopes and southerly aspects), creating diverse conditions that require careful travel.

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