Observation: Porter Fork

Observation Date
Observer Name
Greg Gagne


Location Name or Route
Mill Creek Canyon (Porter Fork)
Wind Direction
Wind Speed
Weather Comments
Occasional gusts of Moderate winds out of the SW along upper elevation ridges.
Snow Characteristics
Snow Surface Conditions
Faceted Loose
Wind Crust
Melt-Freeze Crust
Snow Characteristics Comments

HS between 1 and 2 meters above 8500'.

Snow surface has weakened in the top 5-10 cms (2-4") and was very easy to get sluffs moving in steeper terrain.

Some crusts on southerly aspects, but very easy to ride through. Did notice some facets on top of crust just below surface on south and southwest aspects in Mill B North. (Comments below.)

The weak snow at the surface will likely be the weakest layer initially once we get a new load of storm snow and/or wind.

Red Flags
Red Flags
Recent Avalanches
Wind Loading
Poor Snowpack Structure
Avalanche Problem #1
Persistent Slab
Problem #1 Comments

Am thinking the persistent slab issue is isolated in (1) thinner snow pack areas, and (2) repeater slopes. Have been seeing evidence of generally strong snowpack in much of the terrain I have looked at the past few days. But in isolated terrain, the snowpack is weak and it won't take much of a load to get avalanching.

The isolated terrain is north through east with a thin, weak snowpack. This can be most easily found in steeper, rocky terrain. Also concerned about repeater slopes that have avalanched this season. Outside of this isolated terrain, the snowpack looks generally strong and stable. 

With forecasted snow Thursday night/Friday, and then again later Saturday, we will be adding additional stress on these weak layers.


Let's begin with the good news. First two photos showing areas where there is a strong snowpack. (Arrow shows the dust layer from the strong pre-frontal winds on Sunday afternoon.)

OK, now for the not-so-good news. I had seen a crown from a natural avalanche on a NE aspect with a starting zone on a steep, rocky NE aspect with what appeared to be a thinner snowpack structure. (Photo 1) I had also seen a crown on another slope with similar aspect and elevation, but didn't want to travel underneath avalanche paths to look at it. This too appeared to be a natural, from a likely cornice fall. Each of these slides were class 2, running an estimated 200-300' and 25-75' wide.

I looked at the snowpack structure on an adjacent slope and found a thin snowpack (70 cms/28") with very weak faceted snow and depth hoar. Photo and video. 

This is the type of isolated terrain that should be avoided.


Also was finding a thin layer of radiation recrystallization on south and southwest aspects in Mill B North, as well as in terrain when approaching Gobblers Knob. This layer is 5-10 mm sitting on top of a thin 5 mm crust. Wednesday was clear and cold, but with strong sun, it was type of weather conditions that promote this sort of faceting. With snow in the forecast over the next several days, it is helpful to keep weak layers such as this in mind.

Where I was traveling today, overall hazard was Moderate.

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