Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
December 11, 2022
Submitted:
December 11, 2022
Observer:
NWAC Forecaster - Irene Henninger
Zone or Region:
West Central
Location:
Hwy 2 Corridor (N, S, W up to 4400ft)

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
None Experienced
Collapsing? 
None Experienced

Media/Attachments

Ski penetration was about 20cm.
The storm snow layer at 4400ft. There was still 10cm at 2000ft.
3000-4400' I found snow heights (HS) ranging from 130-150cm.
A small dry loose avalanche, or sluff, which occurred near the end or after the storm 12/10.
Many small rollerballs came down as temperatures reached freezing midmorning.
I mainly found a right-side up snowpack. Storm instabilities produced easy compression test results in top 10cm.
Found CTH results about 40cm down in many pits. It was hard to isolate the layer, but a lot of searching never resulted in surface hoar.
Decomposing forms at the interface of the compression test results down 40cm.
An extended column test yielded no result after I was getting rough breaks in hard compression test results (CTH) about 40cm down. 4350ft, SW.

Advanced Information

Weather Summary

Cloud Cover:
Partly Cloudy
Temperature:
32°F
Wind:
Calm
New/Recent Snowfall:
28cm from 12/9-10 storm

Temps were 28 degrees, rising to freezing by midmorning 3000-4400ft range.

Snowpack Observations

Snowpack heights ranged from 130-150cm from 3000ft upwards. The storm snow layer was still 10cm even at 2000ft. Snow was dry and right side up, ranging from fist hard to pencil hard in the top meter, with no very obvious layer changes. My ski penetration was about 20cm, boot penetration was about 50cm.

I dug several pits and mainly found new storm snow instabilities in the top 10cm failing in the first few taps of a compression test. I got many hard or no result on compression tests on a weak storm interface ~40cm down. I searched for signs of surface hoar that have been reported in other zones but did not have any luck. Extended column tests had no result. The November crust layers were in the bottom 30cm of the snowpack and had no obvious weaknesses.

Small sluffs and rollerballs were visible from during the storm and after. Some were dry, some may have been moist. As temperatures slowly warmed to freezing mid-morning I began seeing tree bombs and many more rollerballs coming down.