Observation: Grizzly Gulch

Observation Date
12/9/2021
Observer Name
Greg Gagne
Region
Salt Lake » Little Cottonwood Canyon » Grizzly Gulch
Location Name or Route
Grizzly - Twin Lakes Pass - Patsy
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
West
Wind Speed
Light
Weather Comments
Short periods of heavier precipitation. Some evidence of wind-drifting in exposed terrain, but winds were light midmorning atop Honeycomb ridgeline at 10,400'.
Snow Characteristics
New Snow Depth
8"
New Snow Density
Low
Snow Surface Conditions
Powder
Snow Characteristics Comments
Right-side up storm snow with denser snow (and some graupel mixed in) early in the storm followed by lower density snow. Some cracking in areas with with some wind-drifting making the storm slab a bit denser.
Red Flags
Red Flags
Heavy Snowfall
Cracking
Collapsing
Poor Snowpack Structure
Red Flags Comments
Was able to get cracking in the storm snow on slopes that held older, faceted snow on the snow surface. Did get a few collapses, but there didn't seem to be enough of a load on top of the facets to initiate collapsing.
Avalanche Problem #1
Problem
New Snow
Trend
Increasing Danger
Problem #1 Comments
New snow was reactive with cracking on northerly slopes that had faceted snow on the old snow surface. Am selecting increasing danger with another round of snowfall expected overnight and into Friday.
Avalanche Problem #2
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #2 Comments
West/Northwest winds had relaxed by the time snowfall began ~6 am, but I was still finding a few shallow soft slabs of wind-drifted snow that were reactive to ski cuts with cracking. Winds are forecasted to increase overnight and into Friday morning - with plenty of low-density snow available for transport, I am expecting more sensitive wind drifts for Friday, especially at the upper elevations.
Comments
The first real storm of the year that falls onto an existing snowpack is always tricky as there is so much spatial variability. Most slopes facing the south half of the compass were bare dirt prior to this storm, so any storm snow instabilities should settle out quickly. The northerly aspects are more of a concern as many of these slopes had a patchwork of weak, faceted snow at the surface. In my field work today I was finding that the new snow was bonding reasonably well to the old snow where the surface was crusted. But on slopes where the old snow surface was weak and faceted, it was very easy to get cracking in the storm snow where the old snow was a reactive weak layer.
I would stay clear of avalanche terrain (slopes > 30°) on north-facing slopes at the mid and upper elevations as there is the potential for avalanches failing on this faceted layer. Avalanches may be triggered remotely and also occur naturally during any period of higher precipitation or any wind-drifting.
Photos are of cracking in the storm snow as well as a very weak pit on a NW aspect right at the transition point between mid and upper elevations.
For Friday's forecast, I am inclined to go with a Considerable danger rating for mid and upper elevation northerly aspects as the storm snow and fresh wind drifts are sitting on top of weak, faceted snow.
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Considerable