Observation: Back of Bobs

Observation Date
01/31/2016
Observer Name
Joey Dempster

Region:

Location Name or Route
NE Shoulder of Bob's Knob, Aspen Grove
Weather
Sky
Overcast
Precipitation
Light Snowfall
Wind Direction
South
Wind Speed
Light
Weather Comments
Mid twenties in the afternoon, but the wind was frigid. Snow started again about 2:00 with perhaps an inch of accumulation by 5:00.
Snow Characteristics
New Snow Depth
6"
New Snow Density
Low
Snow Surface Conditions
Powder
Rain-Rime Crust
Snow Characteristics Comments

There is a mostly supportable rain crust under the new snow up to 8000 feet.  The new snow is sluffing easily both in areas with the crust and above.  I observed some farily large sluffs that ran several hundred vertical feet and entrained enough snow to knock a person over that started in very steep (40 deg) terrain at the top of Bob's.  There were ski cuts from an earlier party along the top and it is probable that these sluffs were a result of the cuts.  They did not trigger any slab avalanches.  In general, given the low amount of new snow, I considered the sluffing today to be very manageable, and the fact that the sizeable sluffs I observed did not trigger any deeper slab avalanches was a good sign.

Red Flags
Red Flags Comments
Other than the sluffing, no red flags in terrain below 9000-8500 feet today.
Snow Profile
Aspect
Northeast
Elevation
8300
Slope Angle
37
Comments

I had been wanting to test the January facets on steeper terrain all week and today got my chance.  The results were positive.  The interface between the late January new snow and the early January facets appears to have gained strength nicely.  7 days after I poked around in this area and didn't find any signs of instability, but was worried about the structure, I was able to dig on a steeper slope (37 deg) and both ECT and CPST indicated stability.  ECT was ECTX and CPST was 75/90 with no column movement.  The facets did collapse at the very end in a haphazard manner, meaning not a single horizontal shear plane, but a kind of zig zag through the layer, but it was short (15cm) and didn't produce any displacement of the overlying snow.  That, combined with a pretty good thump from some sluffing (described above) had me feeling pretty good about the bonding for the first time since it started snowing again.  We (and another party) skied the shoulder without incident, and also skied similar steep terrain a bit lower in the theater of the pines with only sluffing observed.

I would call today's hazard moderate in the mid to low elevations, and only due to the ubiquitous but manageable sluffing.  Probability of slab avalanches is, at the moment, low (not "no"!) in these areas, even on steep slopes.

Skiing and riding is decent but not great.  The crust is mostly supportable on fat skis and snowboards.  Skinny skis can punch through.  Above 8000 the crust disappears and conditions are better.  

Note that I cannot comment on conditions above 9000 feet.  I would still approach the top of Primrose with caution, digging as I went to see if anything is changing with elevation, because it is certainly possible.  

Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Snow Profile Coordinates