11th Annual Utah Snow & Avalanche Workshop Open and Motorized Sessions Oct. 27th.
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Observation Date: 
4/8/2017
Observer Name: 
Joey Dempster
Location Name or Route: 
Primrose Cirque
Weather
Sky: 
Overcast
Precipitation: 
Light Snowfall
Wind Direction: 
Southwest
Wind Speed: 
Strong
Weather Comments: 
Rain, then heavy snow, then high winds. The first part of the storm packed a decent punch, and there were debris piles everywhere to prove it. Drier snow up high was being transported by the afternoon high winds. Lots of spindrift pouring down off of Robert's Horn and East Peak.
Snow Characteristics
New Snow Depth: 
4"
New Snow Density: 
High
Snow Surface Conditions: 
Dense Loose
Melt-Freeze Crust
Damp
Snow Characteristics Comments: 

I topped out at 9000', and even at that elevation, the old snow surface was saturated down 6"-8".  The top of that layer is in the process of refreezing, but is not yet supportable.  On top of that is 3"-4" of very dense "sierra cement" up to about 8000 feet at which point it gradually changes to slightly drier "styrofoam".   I thought the descent was going to be forgettable at best because of the breakable crust under the new snow, but with fat rockered skis, it actually skied quite well, and I'd go back and do it again without reservation.

Red Flags
Red Flags: 
Recent Avalanches
Heavy Snowfall
Wind Loading
Poor Snowpack Structure
Avalanche Problem #1
Type: 
Wind Drifted Snow
Trend: 
Same
Problem #1 Comments: 

Wind slabs from Saturday will be confined to the highest elevations.  Probably manageable.  Moderate hazard.

Avalanche Problem #2
Type: 
New Snow
Problem #2 Comments: 

The new snow that fell after the changeover from rain to snow is warm and dense, and should provide an excellent bonding surface for new that falls Saturday night and Sunday morning.  If that were the only factor, I would say hazard tomorrow would be moderate, perhaps even low.  However, the wild card is the saturated snow underneath the 3"-4" of new snow.  The saturated snow is quite weak and uncohesive.   It has the advantage of having quite a bit of friction, and with a small load on top of it today, there were no signs of instability, either slab or point release.  But with an additional significant load on top of it, I would approach it with caution, since it's an unfamiliar structure.  

It is possible that enough heat will be drawn out of the saturated portion of the snow back that it will become supportable.  If this happens, I would expect stability to be excellent tomorrow.

Comments: 

The photo below is one of the debris piles in Primrose that ran early Saturday morning.  (Forecaster note: timing of these slides is unknown.)  This one is significant because it was part of a larger avalanche that ran down from the high cliffs of east peak down towards the Falls Couloir.  Normally, all of the debris gets channeled into the couloir.  In 20 years of skiing in Primrose, I don't recall seeing this much of that path's flow diverted down into the small bowl to climber's right of the Falls Couloir  (That's not to say it has never happened, just that it's not frequent enough for me to have noticed).  I interpret this to mean that these types of avalanche paths are so deeply filled with debris that it is potentially causing debris flow that is out of the ordinary.  So caution is warranted in areas that you might normally consider out of the runout zone for large avalanche paths.   It is difficult to say whether the weakness that caused this cycle Friday night into Saturday is still present, and could reload with new snow, or if it got washed out or perhaps cooled down enough that the new snow will not produce a similar cycle tomorrow.  It would be prudent, I think, to assume that the weakness will persist and give these big paths a wide berth tomorrow.

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

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