Large natural wind slab, a bit too close for comfort

Date of Observation: 02/17/2023
Name: Zach Guy

Zone: Northwest Mountains
Route Description: Mineral Point, targeting wind slab instabilities on east to south aspects to 11,600′. Our plan was to cross under the south face of Mineral early morning before it got too warm. After several delays this morning (2 dead car batteries!), we didn’t cross beyond the most exposed sunbaked terrain until 11 a.m., which in hindsight, was cutting it too close for the type of terrain that we were on.

Observed avalanche activity: Yes
Avalanches: A large natural wind slab released off the south face of Mineral around 11:15 a.m., triggered by solar warming or perhaps a very tiny wet loose. The debris washed over part of our skin track that we had set an hour earlier.
Evidence of a widespread storm slab cycle in the Slate during the storm, along with numerous wind slabs in Poverty Gulch that ran after the storm, likely during yesterday’s northerly winds, up to D2 in size. See photos.
Weather: Clear, calm winds. Rapid warming; Double puffy snowmobile ride (-20F at TH), down to sun shirts once we started skinning. At one point, I looked over and my partner’s bare butt was showing, frantically trying to remove his long underwear. haha.
Snowpack: North winds did a lot of damage in Poverty Gulch, with wind slab formation scattered across all elevations. Wind slabs are easy to recognize: smooth, stiff snow (6″ to 12″ thick, 4F to 1F) below rollovers and in gullies, in contrast to softer, rippled sastrugi elsewhere. Wind slab feedback was stubborn underfoot. I snowmobiled and ski stomped on over half a dozen suspect wind-loaded rollovers without any signs of instability or cracking. However, I could produce cracks up to 5 feet while stomping on slopes undercut by the skin track. I also got easy test results on wind-drifted slopes (ECTP1, ECTPV). All of the wind slabs in this area, and my test results, failed on a low-density precip particle layer (non-persistent). Tests on the 2/13 storm interface were unreactive. I tested an east-facing slope near treeline which had a thin crust above facets at the storm interface.