Observation: Main Porter

Observation Date
12/15/2021
Observer Name
Gagne/Pease
Region
Salt Lake » Mill Creek Canyon » Porter Fork » Main Porter
Location Name or Route
Main Porter Fork
Weather
Sky
Few
Wind Direction
Northwest
Wind Speed
Moderate
Weather Comments
Gusty winds noted along exposed ridges, but no wind effect down lower in drainages. It seems wind effect is likely confined to ridges.
Snow Characteristics
New Snow Depth
14"
New Snow Density
Low
Snow Surface Conditions
Powder
Snow Characteristics Comments
30-40 cms new storm snow that came in right-side up. Just a few cms of denser snow at the onset of precipitation on Tuesday night and most of the snowfall was low-density stellars.
HS (height of snow) at 8,000' is 1 meter.
Red Flags
Red Flags
Heavy Snowfall
Collapsing
Poor Snowpack Structure
Red Flags Comments
Several loud collapses today, but no cracking or remotely-triggered avalanches. No evidence of any avalanche activity overnight.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments
I was finding a snowpack structure in Millcreek similar to what I've been seeing in Little and Big Cottonwood as well as along the Park City ridgeline with a slab from recent storms on top of weak facets, but the PWL down near the ground is only about 15-30 cms thick above ~7k in Millcreek. This is likely due to this zone not getting as much early-season snowfall.
Comments
First time in Millcreek this season and storms from late last week and Tuesday night have greatly helped coverage in this area. I essentially found similar conditions to DB's observation from 12/14 - same structure as found in the Cottonwoods, but just a shallower snowpack. Despite not seeing any avalanche activity, the collapsing is definitely a red flag and will continue to make me wary on the northwest thru east aspects where the PWL is present.
The North American Danger Scale identifies three components to a danger rating: 1. Likelihood; 2. Size and Distribution; and 3. Travel Advice. Although the likelihood of avalanches today was more aligned with a Considerable danger rating, recent avalanches, poor snowpack structure, and heavy snow overnight made for travel advice following the High danger rating where travel is not recommended in avalanche terrain where the PWL is present.
Today's Observed Danger Rating
High
Tomorrows Estimated Danger Rating
Considerable
Coordinates