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Observation: American Fork

Observation Date
2/25/2024
Observer Name
Kelly
Region
Provo » American Fork
Location Name or Route
Upper American Fork Canyon & Mary Ellen Gulch
Weather
Sky
Clear
Wind Direction
West
Wind Speed
Moderate
Weather Comments
Clear skies, winds were moderate gusting to strong from the west and northwest through the day. I observed some snow transport and flagging (snow off the highest ridgelines).
Snow Characteristics
Snow Surface Conditions
Dense Loose
Melt-Freeze Crust
Damp
Snow Characteristics Comments
Throughout the day the constant was a smooth snow surface. That varied from dense loose slightly faceted on the northerlies to melt-freeze cust in either melt or freeze form depending on how much sun had affected the surface. There was some breakable crust earlier in the day.
Surprising lack of weak surface conditions and surface hoar compared to surface from further south in the Provo Region.
Avalanche Problem #1
Problem
Wet Snow
Problem #1 Comments
Photo below of a wet loose avalanche that propagated out in the middle of the slide path. This slide was most likely from 2/25/2024. It started at 10,600' and ran to about 9,400' on a southeast aspect in upper American Fork Canyon. The roller balls lookers right of the slide were more noteable near rocks and cliff bands and below 8,000' on south and east facing I was able to initiate wet loose roller balls on steeper slopes. This trend will remain the same as temperatures remain warm.
Avalanche Problem #2
Problem
Persistent Weak Layer
Trend
Decreasing Danger
Problem #2 Comments
I dug 3 snowpits all on southeast facing aspects to see how the PWL that has been the culprit of avalanches on east and southeast facing terrain was responding to the warm temperatures. I was not able to get propation on this layer and found that in one snowpit the temperatures were all 0°C or 32°F which shows an isothermic temperature profile and leads to rounding in the snowpack. See below for pit details.
Snow Profile
Aspect
Southeast
Elevation
10,200'
Comments
3 snowpits below on southeast aspects above 10,000'. Layer of concern from 2/14/2024 interface was 27" (70cm) from the surface in the 10,870' pit and 20" (51cm) from the surface in the 10,100 pit, which matches the depth of the weak layer in the snowmobiler triggered avalanche on Miller Hill from 2/22/2024 where the weak layer was 22" (55cm) from the surface. In this case after 2 days of above freezing temperatures we were not seeing propagation with extended column tests on this layer in two of the snowpits and didn't find the layer in the third snowpit (highest elevation, maybe the most wind affected terrain?).
These 3 pits highlight the variability of slopes in the Central Wasatch right now and while this layer isn't showing us weaknesses with stability tests right now it was just three days ago. Warm temperatures are helping and lack of avalanche activity is a good sign. With the upcoming storm we will continue to watch this layer to see how it is reacting to additional snow and wind loading.
The last avalanches on this layer that were reported to the UAC:
Salt Lake Region:
Caribou Basin- February 21, 2024 SE Aspect- 10,200'-2' deep x 100' wide (skier triggered intentionally)
Caribou Basin- February 23, 2024 East Aspect- 9,500' 4' deep x 100' wide (snowmobiler triggered)
(Maybe failed on PWL facets) Dog Dish on February 24th- East Facing 9,800'
Provo Region:
Miller Hill- February 22, 2024 SE Aspect- 9,800'-2' deep x 1400' wide (caught 2 people)
Elk Point- February 22, 2024 East Aspect 8,800' 14"-16" deep x100' wide x 700' vertical (unknown trigger)
Ogden Region:
Chilly Canyon Slabs-February 22, 2024 East Aspect-6,700'-12" deep x 250' wide (natural)
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
None
Coordinates