Observation: NWAC Observer

Advanced Information

Weather Summary

A beautiful day. Clear and calm with strong late February sunshine. Temps remained cool in the shade.

Observed a few small sz.1 Wet to Dry Loose Natural avalanches, emanating from steep solar terrain and running <100m with minimal entrainment.

Snowpack Observations

Traveled multiple aspects around the headwaters of the Hairpin Valley, Copper Creek, and the N.Fork Twisp today, looking at snow surfaces, digging profiles within the upper snowpack, and enjoying the great ski quality.
As of today, snow surfaces on polar aspects tended to consist of small near-surface facets, easy to identify by their lack of cohesion and tendency to sluff on the steeps. Surface Hoar was present (up to 3mm) on these colder aspects as well, but I observed it to be totally flat-lying and very patchy in distribution, having recently been swept by northerly winds.
On solars, interestingly, the Surface Hoar was uniformly larger and much more continuous in distribution, presumably spared by the recent northerly winds. The strength of the sun today had flattened the SH, and it was bonding and decomposing amidst moist surface snow. Nonetheless, it was observed intact up to 7500' today on SE thru W aspects.
Deeper, the structure of the upper snowpack on solar aspects was observed to be quite favorable. In a profile on a south aspect at 7200', about 25cm recent storm snow was well-bonded to a 40cm thick, very strong crust. I was unable to initiate any wet loose activity today with ski cuts on steep features.
On colder aspects, the upper snowpack structure is less confidence inspiring. Although not problematic at present, it will be worth keeping in mind, as storm snow once again begins to stack up. In a profile on a NE aspect at 6400', I found 25-30cm recent storm snow over a 25cm thick mass of laminated melt-freeze crusts and faceted grains. The bond with the upper most crust (mid-Feb. interface) was favorable. Compression Tests yielded hard breaks within the faceted laminations, down about 40cm, and ECT's demonstrated a lack of propagation potential. Again, given the lack of significant overlying slab, this structure is very forgiving at present, allowing skiers to chip into many steep lines over the past week with no avalanche problems other than dry loose. A big storm could quickly change the game, necessitating a big step back in terrain selection.

Avalanche Problems

Problem	Location	Distribution	Sensitivity	Size	Comments
Wet Loose	N E S W	Isolated Specific Widespread	Unreactive Stubborn Reactive Touchy	D1 D1.5 D2 D2.5 D3 D3.5 D4 D4.5 D5	Comments: The bond between recent storm snow and underlying crusts has much-improved on solar aspects over the past few days.