Observation: Back of Bobs

Observation Date
01/24/2016
Observer Name
Joey Dempster

Region:

Location Name or Route
Back of Bob's, Aspen Grove
Weather
Sky
Overcast
Precipitation
Light Snowfall
Wind Direction
North
Wind Speed
Moderate
Weather Comments
Almost no accumulation of new snow after 9am. Moderate ridge top winds with some transport, but not significant. Warm temps with medium density snow.
Snow Characteristics
New Snow Depth
8"
New Snow Density
Medium
Snow Surface Conditions
Powder
Snow Characteristics Comments

Nice shot of slightly heavy snow that skied really well over the crusts and in general was well behaved.

Red Flags
Red Flags
Poor Snowpack Structure
Red Flags Comments
No problems with the new snow, but facets about 45 cm down (the snow that faceted in early Janurary in between storm cycles) is very obvious and troubling.
Avalanche Problem #1
Type
Persistent Slab
Trend
Same
Problem #1 Comments

20cm of new snow in this storm, with about 25cm from the Wednesday storm have buried the old faceted snow surface.  It is not just a thin layer of surface recrystalization of surface hoar, but several centimeters of poorly bonded, small grained facets. It is not consistently reactive in stability tests, but it doesn't have  much of a load on it yet.  However, that's cold comfort to me on a steep slope, and I chose to avoid steeper terrain (sustained pitches of over 33-34 degrees) in an abundance of caution. I think this layer will heal fairly quickly, but it still needs a few more days at least to start showing some cohesion.  I don't think this is an acute problem, as I did not observe any avalanches or cracking/collapsing, and I'm sure you could have gotten away with skiing it in most places.  But for me, it's presence, along with a new 8" load on top of it, was a significant factor in my decision making today.  And, as I said above, I think I'll continue to monitor it for increased bonding before I trust it.  

Snow Profile
Aspect
East
Elevation
8500
Slope Angle
28
Comments

ECTX (in two different places, both 28 deg.) was helpful but not conclusive to me. I still want to give those facets some more time.  I would like to repeat them on some steeper slopes, but I could not find any that were safe to access today.  I know that ECT is fairly independent of slope angle, but I still didn't want to be the first person to stick my nose into a 38 degree slope with this structure.  Not yet.

I also dug (and skied) in some south facing terrain and found that the new snow bonded well to the m/f crust, at least at the mid elevations, so I don't think that this is as much of a concern as I thought it would be yesterday.

It should be noted that Wednesday's snow has consolidated to (at least in the 2 pits that I drew this consolidated profile from) 1 F snow already.  It could be windpacked in these locations, but in any case, there is definitely a slab overlying the facets.  It's not huge and isn't obviously overburdening the weak layer yet, but it is definitely a case of "strength over weakness", and not just fluffy new snow.  

I found hazard to be moderate in mid elevation terrain, due to good bonding of the new snow, and lack of any red flags other than the buried facets, and even they didn't seem to be "screaming".   I did not, however, feel like marching up Primrose Cirque would have been prudent today, so I would consider that to be an overall CONSIDERABLE hazard.  I feel like it will be little changed tomorrow, since the root of this hazard is buried facets, and the recent new snow is formed into a relatively cohesive slab in many places.

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