The main objective today was to investigate the surprising D3 avalanche on a SE facing slope NTL in Nirvana Bowl that ran during last week's storm.  In its current state, the crown features a mostly dry, hard slab (1F to P) averaging 4 feet thick, with dozens of frozen ice columns and ice lenses (up to several cm thick) throughout.  The avalanche failed on depth hoar at the ground, which was previously wet and is now refrozen melt forms in some parts of the crown, or remains dry with ice lenses through the layer in other parts of the crown.  We hypothesize that this avalanche failed as a wet slab.  The record-breaking warmup preceding last week's storm caused meltwater to drain into the depth hoar, amplified by the cliff band above the slope. Under the insulation of the overlying slab and new snow, the weak layer probably remained wet through the loading period, and the storm added enough stress to cause a failure. The avalanche was a step-down triggered by a shallow wind slab above.  A really interesting and unique avalanche - I haven't seen a slide like this in Crested Butte before!

Original CBAC ob: https://cbavalanchecenter.org/view-observations/#/view/observations/9f1476a0-4f4c-4197-847a-32be9e06fc1d

Baldy Traverse

Snowmobiled to Elkton. Traversed on skis across Rock Creek Bowl, Quigley Bowl, Nirvana Bowl to Emerald Bowl, traveling on southerly and northerly aspects near and above treeline before returning via Schofield Pass Road and Rock Creek.

Updated details of the attached avalanche.

The pre-storm snow surface near and above treeline here consists of melt-freeze crusts (lacking any overlying weak snow) on southerly aspects and small-grained facets (~.3 mm) on dry northerly aspects.  Winds were moving the dry snow around in some areas, helping to damage it. I only looked at a couple of below treeline east-facing slopes; the radiation recrystallization grains that formed earlier this week were getting warm from today's greenhousing; I'm uncertain how much of the layer survived.  A ~1mm surface hoar layer formed below treeline in Washington Gulch overnight; it was cooked down on the flat roadside slopes that we traveled on this afternoon.  .

Traveled on numerous steep slopes on various aspects without signs of instability. We generally traveled where the snowpack was deep, but also crossed a few shallow wind-eroded features.

Variable cloud cover and moderate wind speeds. Some upper elevation slopes holding dry snow saw saltation of near surface layers. wind loading: none; recent snowfall (cm): 0; snow avail for transport: small smounts