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Observation: Greens Basin

Observation Date
1/29/2013
Observer Name
Greg Gagne
Region
Salt Lake
Location Name or Route
Silver Fork - Greens Basin
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
West
Wind Speed
Moderate
Weather Comments
No wind affect off of ridge lines, some Moderate gusts along ridges.
Snow Characteristics
New Snow Depth
5"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments
About 10-15 cms (4-6") new overnight of very light density snow. Some wind drifted snow along ridgelines > 8500'. Wind drifts were sensitive and cracks were propagating. Wind drifts were 4F and ranged from 5-30 cms (2"-12"). New snow sluffed very easily on steeper aspects and several natural sluffs were observed.
Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Collapsing
Poor Snowpack Structure
Red Flags Comments
Alot of red flags were present today. New snow over the past 2 days, recent wind loading, widespread natural sluffing in the new snow. Several collapses as well as cracking in the new snow as well as wind-drifted snow. Scales hadn't tipped, but clearly the snowpack was talking and an increase in new and/or wind-drifted snow may be enough to overload weaker buried layers. (Not to mention manage storm snow instabilities.)
Avalanche Problem #1
Problem
New Snow
Problem #1 Comments

Was finding a much weaker snowpack in Greens Basin today than I had seen in some other mid-elevation areas of BCC. Buried facets from Jan 1-8 faceting event are buried about 50-60 cms down and they were much weaker than in other areas where I have been traveling. This layer was 10 cm thick with 4F hardness. We were getting several collapses (presumably on this layer) and were unable to isolate a column as it failed on this layer as well.

In my obs from Jan 28 I indicated that at mid-elevations I was generally finding the faceted snow from the two January faceting events to not be overly concerning. Today made me rethink that and I suspect there is a greater spatial variability of the strength/weakness of this persistent weak layer than I had originally thought.

Comments

New snow is light density and not acting as a cohesive slab. Where there hasn't been wind loading, I still don't think there is enough new snow to overload buried weak layers, but we seem to be getting close to that point. In areas where there has been significant wind loading, we may have passed that point.

Highlights today:

  • Several natural sluffs
  • Easy shears (STE) failing on graupel layer down 35 cms at the interface of Jan 28 snow.
  • Unable to isolate a column on E/NE 28 degree aspect at 8800'. Q1/SP failing on early January facets down 55 cms.
  • Several collapses
  • Fresh, sensitive wind deposits in leeward terrain

Sounds like a broken record, but current conditions warrant terrain management as the key to safely travel in avalanche terrain.