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Professional Observation

Basic Information

Observation Details

Observation Date:
December 20, 2019
Submitted:
December 20, 2019
Observer:
Pro
Zone or Region:
Banner Summit
Location:
Copper. 6700- 8900' all aspects

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
first ones up the standard SW ascent ridge. newly developed 4F windslab with collapsing.

Bottom Line

would consider adding windslab to problems in upper elevation in this zone. some large collapses and one new avalanche seen in windloaded area in last 24hrs

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Temperature:
above freezing
Wind:
Moderate , S

7 - 12cm H24. dense snow. evidence of strong winds --> upper S-SW aspects scoured down to sagebrush (HS only 10cm on upper elevation SW aspect

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Past 24 hours upper west face Copper Mtn
W 8800 		D1 SS I-New/Old Interface 20 N-Natural on upper elevation windloaded aspect. did not step down to the buried 12/7 loc None
1 Within the past week N aspect , eastern summit of copper mtn ridgeline
N 8800 		D2 SS O-Old Snow 50cm U-Unknown bed surfaces now partially buried by recent snow and windloading. appears occurred with last storm likely running on 12/7 based on depth None

Snowpack Observations

NE aspect (30 deg), 8600'. 20* HS 105. 12/7 down 50cm. basal FC 0-45 4mm dry.
ECTN13 down 30
PST cross slope 40/100end down 50 on 12/7

W aspect (90 deg) 8600' 30* HS 95. 12/7 down 50cm basal FC 0-25cm 2-3mm wet.
ECTP13 down 50 on 12/7, loc still showing 10-12mm SH in failure plane (see photo)

buried SH from 12/7 still main culprit consistently seen in failure plane in stabilty tests. Here ectp13 (w aspect @8600')

Avalanche Problems

persistent slab - not sure what to make of ECTN results on 12/7 N aspect. overlying slab did seem a bit softer here, perhaps S and W aspect overlying slab a bit more cohesive.
wind slab - isolated on ridgelines and in lee, but hard to ignore. shooting cracks, a few impressive collapses today and a natural from last 24.

Terrain Use

did not ski on avalanche terrain. was hoping to ski upper elevation S, SW, but windscoured to sagebrush.

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