One recent natural slab avalanche that occurred yesterday was observed up Valley of Sin. See photo.
Observation: Hatcher Pass
Location: Marmot- South ridge to Mid-rib to the Nose
Post storm tour to assess stability and storm totals. The recent 4/4 storm brought 10″ of new snow mostly right-side up, bonded well to most snow surfaces. We observed one natural persistent slab avalanche up the Valley of Sin. One human triggered avalanche was triggered on lower Microdot today. Several small dry loose sluffs were observed in steep terrain on multiple aspects.
Observer Comments
Weather
-Road conditions were a little rowdy getting to the Fishhook Lot around 1000 with new storm snow on the ground.
-Morning temps at 0800 on Marmot were still in the teens @ 15°F. By 1100, these warmed to 23°F.
-Below 3,000', there was valley fog most of the morning until 1300 when it looked to be breaking up. Cloud level above 3,000' was intermittent with broken skies and noticeable warming of the snow surface (see photo).
Snow surface
New snow felt right side up and dry on our way up. Ski penetration on the uptrack up Marmot from Fishhook was between 7-10" most of the way. By the afternoon, sun effect increased temperatures in the top 5cms and we were clearly seeing signs of warming with glopping, easy snowballs and thick feeling snow surfaces (see photo).
Snowpack
We dug just below ridgeline in the Midrib. We observed failure in snowpits within the new snow and March melt freeze crust. Test results just below ridgeline were CT16SC (sudden collapse) in near surface facets just below the crust. These crusts are intermittent and very in cohesion (see photo).
Slightly lower down the Mid Rib (4,100' NW HS245) with deeper snow, results were less noteworthy with ECTX, CTN. 1mm founding near surface facets on 1F>P hard crust down 80cm was the most concerning layer. Neither pits observed graupel on crusts from the beginning of 3/31 storm.
On more E-S-W-NW we are seeing them to be more supportive with more developed facets below.
By 1400, there was noticeable warming in the upper snowpack. New storm snow began to behave more slabby and cohesive.
4/4 Natural avalanche on Ripper's Delight in the Valley of Sin NW 4200'
4/5 Human triggered small dry loose sluff , Marmot SSE 4200'
Debris from 4/5 Human triggered small dry loose sluff , Marmot SSE 4200'
Top 60cm of the snowpack @ Marmot Mid Rib. We saw failure on tests below the March MFC on facets.