Pro Field Report

Basic Information

Observation Details

Observation Date:
December 29, 2021
Submitted:
December 29, 2021
Observer:
SAC - Davis
Zone or Region:
Galena Summit and Eastern Mtns
Location:
Between Boulder Ck and Dry Ck (All aspects, 6,400-8,500')

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
No visibility but no recent avalanches were observed in Dry Ck.

Snow Stability

Stability Rating: 
Good
Confidence in Rating: 
Low
Stability Trend: 
Steady

Bottom Line

I observed surface hoar buried beneath the series of storms that began on 12/19-12/22 on S-SE-ENE aspects up to 6,900'. This matches similar obs of this layer from nearby Durrance and in Eagle Ck. This layer is worth watching in areas where the snow surface is stiffened by the wind, and/or as the overlying, low-density slab starts to gain strength.

Media/Attachments

(12/29/21) This snowpit was dug at 8,500' on a W aspect in the Boulders W of the SNRA. Roughly half of the snow (down to the line) is snow since 12/19. The other half of the snow is mostly snowfall between 12/11-12/17 and the grey snow at the base is from early October-early December.
(12/29/21) This snowpit was dug at 6,850' on a ENE aspect in the Boulders W of the SNRA. Roughly half of the snowpack is snow since 12/19. The other half of the snowpack is snowfall between 12/11-12/17.
(12/29/21) Surface hoar buried beneath the series of storms that began on 12/19-12/22 on S-SE-ENE aspects up to 6,900'. Boulder Mountains, W of the SNRA.
(12/29/21) This snowpit was dug at 6,850' on a ENE aspect in the Boulders W of the SNRA. Roughly half of the snowpack is snow since 12/19. The other half of the snowpack is snowfall between 12/11-12/17. The snowpack test failed between these two storm events (ECTP21).
https://youtu.be/aFrPCzwq4Uc

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
10-15 F
Wind:
Light , W
New/Recent Snowfall:
HST since 12/19 = 40-50 cm

Light snowfall today produced about 1-2". Wind was sifting snow but not building slabs where I was. The sun was behind a thin veil of clouds all day.

Snowpack Observations

6400-8500', HS = 70-110 cm
Slab over 12/19-12/22 = 40-50 cm
Slab over 12/11 = 85 cm @ 8,500'

I observed surface hoar (SH) beneath the storm that began on 12/19-12/22. I found it on S-SE-E-ENE aspects up to 6,900'. This matches nearby observations by Antonioli on Durrance (multiple aspects and elevations up to 7900') and in Eagle Ck (NE aspect, 6600'). I did not see SH in a pit at 8,500' on a W aspect, but there were facets there and a hardness change from 4F to P (ECTN25). Either setup is worth keeping an eye on as the overlying slab gains strength.

The old October-early December snow was present on the 8,500' W aspect I dug on but was thin and inconsistent. It did however propagate a fracture during an ECT with non-standard added force. I imagine the results would have been easier and repeatable just around the corner on a NW aspect. It's notable that the 12/11 interface is only 85 cm deep here.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 85 cm
Weak Layer(s): Dec 11, 2021 (FC)
Comments: Shaded where the 12/11 layer is known to be at its worst.

I'd like to see more evidence of the surface hoar and facet layer in other areas before calling it a widespread problem, but it's certainly worth looking out for in this zone.

Terrain Use

I closed avalanche terrain where old October snow was anticipated near the ground. Given the surface hoar layer, I would have avoided steep middle elevation terrain where wind-loaded.