Pro Field Report

Basic Information

Observation Details

Observation Date:
January 15, 2021
Submitted:
January 15, 2021
Observer:
SAC - Chris Lundy
Zone or Region:
Banner Summit
Location:
NE corner of Banner Summit zone (7500-9100', visual on most aspects, traveled on mainly E)

Signs of Unstable Snow

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

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Moderate
Stability Trend: 
Improving

Bottom Line

The December weak layer is buried beneath a 3+' thick, very dense slab at mid and upper elevations. The lack of natural avalanches breaking into deeper layers as a result of the past storm indicates that maybe this instability is improving. But I would not trust my life to this snowpack structure - if you triggered a slide, you probably wouldn't survive it.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
warm
Wind:
Moderate , W
New/Recent Snowfall:
S1 to S2 snowfall began around 1430, 2cm HN on the truck when I returned to the TH at 1600.

Some sunshine this morning, then increasing clouds through the day. By noon it was full overcast, and snowfall began midafternoon.

Avalanche Observations

While the light was fairly flat, I had good eyes on a lot of prime-time avalanche terrain. I saw several mid-storm wind slab avalanches less than D2 in size, but I did not observe any persistent slab avalanches - which was surprising.

Snowpack Observations

1-2cm thick rain crust found up to 7500'. Snow surface above that was dense/stiff - made for punchy skiing but decent sledding. Probing and snowpit described below indicate the 12/11 weak layer is buried around 1m deep at mid and upper elevations. Lots of wind effect at upper elevations, but wind slabs no longer seemed reactive.

@8650', E, 23*: HS 140cm. 12/11 buried 1m down - see photo. ECTX x2, but both propagated with very hard hits. CPST 35/100end. Oddly, the solstice crust was not found in this pit??

Snowpit in the northeastern Banner Summit zone shows a 3+' thick, very dense over the December weak layer. This is a true deep slab instability - difficult to trigger, but would produce a very large avalanche.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Deep Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 90-100cm
Weak Layer(s): Dec 11, 2020 (FCsf)
Comments: Rose indicates observed terrain. No natural avalanches observed to break down to this layer. CPST 35/100end. Weak layer is gaining some strength, but structure remains intimidating.

Lots of wind effect at upper elevations, but wind slabs no longer seemed reactive.

Terrain Use

I traveled on some small slopes in the low 30s, but generally avoided avalanche terrain.