Observations

Upper Headwall Avalanche

February 24, 2021 at 12:00 PM
Name: Ryan Lewthwaite| MWAC
Location: Upper Headwall Avalanche

A warm day with 28F degrees in the alpine and 42F degrees at Pinkham Notch. There was ample cloud-cover for most of the afternoon with short bursts of sunshine and snow. The winds were calm during my observation but earlier westerly winds were of gale strength peaking at 103mph. Loose snow was actively blowing from ridgelines and settling lower on the fetch of Tuckerman’s Ravine. A large avalanche had occurred overnight in the Upper Headwall with debris piled in the drainage below. (SS-N-R2-D2.5-O) This describes that the natural, soft-slab avalanche was small relative to the overall path but large enough to bury a person or break a few trees. The size of the avalanche was 125 feet wide and ran downhill over 400 feet. It is important to note that the wind slab avalanche broke below a prominent ice bulge and slid on the knife-hard refrozen crust from the 157mph wind event. This impenetrable crust layer has been the interface for several recent avalanches and is the surface of the snowpack in the mid and upper elevations. Steep, leeward facing, terrain with newly deposited wind-blown snow is where our current avalanche problem exists. The new snow easily slides on this layer and drifted slabs can be over one foot thick. Avalanche paths that have not released the rapidly depositing wind-blown snow should be considered suspicious.