Pro Field Report

Basic Information

Observation Details

Observation Date:
December 17, 2019
Submitted:
December 19, 2019
Observer:
SAC - VandenBos (off duty)
Zone or Region:
Galena Summit and Eastern Mtns
Location:
Central Boulder Mountains

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
Isolated cracking where stiff wind drifts rest on slick alpine surfaces.

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Stability Trend: 

Advanced Information

Weather Summary

Temperature:
inverted
Wind:
Moderate , W

Clear skies at start of tour (afternoon), high stratus pushing in by mid afternoon. Moderate wind blowing out of the west with period strong gusts. Pretty quiet for the Boulders.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 NE 10,200'
NE 10,200' 		D2 HS O-Old Snow N-Natural Didn't get a good look at debris, but based on location (heavily wind loaded, alpine) the slab was probably fairly stiff. Poor light, but bed surface looked dark/dirty - may have run on 11/26 interface which was likely preserved but fairly thin in this area
This avalanche occurred on a NE-facing slope in the Boulder Mountains at 10,200'. It was spotted on 12/17 but failed during the storm a few days before.

No avalanche activity observed on the west side of the range, but it looked like the wind had been blowing so hard that evidence of mid-storm slides would have been erased. Light was not great by the time I got up high and my time was limited so I didn't get to do an exhaustive search. Avalanche on 11/26 DH (?) is worrisome, we're already playing the cumulative loading game and I'm looking at this sort of activity as an indicator of what may be to come.

Snowpack Observations

Boulders are off on their own program, as usual. 12/7 surface hoar seems to be reasonably well preserved down in the foothills (watched it get buried live on 12/7), but distribution became pretty irregular as you enter middle elevations, though I was traveling in the trees in these elevations at the change in radiation balance there may have been responsible for this. Down low, 12/7 interface was probably too "rough" (think sagebrush and rocks) on solars to produce widespread problems, but I'd imagine it could get touchy on low elevation shadies. 12/7 interface isn't particularly attractive even in the absence of SH. Thin MFcr+FC exist on solar aspects, small FCs without a crust on shadies. Need to find relatively sheltered, middle elevation terrain to find these layers preserved well. If you have favorite mid elevation powder stashes in the Boulders they probably won't behave nicely when they get a big load. Up in the alpine the depth and character of snowpack is primarily a function of wind, with many areas scoured down to talus and other with meter plus, P-hard, stiff wind pack.