Pro Field Report

Basic Information

Observation Date:

December 23, 2022

Submitted:

December 24, 2022

Observer:

SAC - VandenBos

Zone or Region:

Galena Summit and Eastern Mtns

Location:

Butterfield (6,800-8,000', N-NE-E-SE-S)

Recent Avalanches?

None Observed

Cracking?

None Experienced

Collapsing?

Isolated

I experienced two muffled collapses that appeared to involve large wind dunes created during the solstice wind event.

Stability Rating:

Fair

Confidence in Rating:

Moderate

Stability Trend:

Steady

The weak snow near the ground is becoming more difficult to impact with the weight of a skier, but the structure is poor and the weak snow is not healing quickly. Triggering a large avalanche involving this snow remains a sobering possibility.

Advanced Information

Cloud Cover:

Obscured

Wind:

Light , W

New/Recent Snowfall:

3-4cm HST, 15-20cm since 12/20

Afternoon weather obs: light snow falling for much of my tour, with daytime accumulation of 3-4cm. Winds were calm to light in the lower and middle elevation terrain I traveled in.

Avalanche Observation Comments:

I did not observe any new avalanches, but I could not see very far thanks to the weather.

My primary goals were to spend some time walking through an untraveled snowpack in this area, to dig down to my old friend the 11/27, and look at 12/8 and 12/19. 11/27 and 12/19 did not look good, 12/8 was not an obviously concerning interface in my pit but has not left my problem list.

My time was limited but I skinned through a fair bit of terrain that had not seen skier traffic this year. Snowpack structure here is poor (as with just about everywhere else) but the thick slab of overlying snow was preventing me from easily impacting the weak layer and I did not experience any large collapses that involved this layer. I dug down to it on N/NW and E/SE slopes at the transition between lower elevation and middle elevation.
-On N/NW aspect at 7,500' I found 11/27 as well-developed 2-2.5mm cupped and partially striated FC, down 85-90cm. Slab hardness was 1F to 1F+ for a 30cm interval at the base, grading to F- at the top. This layer produced ECTP25 x 2 and ECTN 23, and CPST 23/100 and 25/100 END. 12/19 was down 15-20cm, and presented as an airy FCsf matrix. This was once a discernable rain crust from the 12/11 rain event but has faceted away at this elevation, leaving a pretty ugly weak layer. The wind event disrupted this layer in many places, but where it is intact it doesn't look good. I received ECTN 2 and 4 and ECTP 2 and 3 on this interface, impressive for such soft slab. CPSTs produced SF results with cut lengths in the teens, though I could get the fracture to propagate across about half the column as I continued cutting. I did not find a concerning interface at 12/8 in this pit.
-On E/SE at 7,800' I found 11/27 down 70-75cm, presenting as 1.5-2mm FC sandwiched between two crusts. This produced ECTP 22, 25 and 30, and ECTN 21. I did not perform CPSTs on this, due to the roughness of the layer. 12/19 looked very similar in this pit as my other pit and produced ECTPV, ECTP1, 3, 4, and ECTN 3. Again, impressive for a F- slab. I did not find a concerning interface at 12/8 in this pit.

My interpretation: we continue the trend towards decreasing likelihood with 11/27, but still hard to describe it as a deep slab problem here. In my mind, if I can repeatedly initiate and propagate fractures in ECTs we aren't in the unlikely category, but rather still well within the realm of possible. This agrees with CMAH widespread+stubborn description. Stepping back, the idea of the possibility of triggering D2-D3 avalanches in most avalanche terrain keeps me from entering large, consequential avalanche terrain. We are not done with 11/27 yet.