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Professional Observation

Basic Information

Observation Details

Observation Date:
December 27, 2020 - December 29, 2020
Submitted:
December 30, 2020
Observer:
WAC - caleb merrill
Zone or Region:
Southern Wallowas
Location:
Norway Basin, East Fork Pine Creek

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
None Experienced
Weak Snowpack Structure. Unstable PST results

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Stability Trend: 

Bottom Line

Weak snowpack structure observed on W-N-E aspects where the Solstice Rain Crust (SRC) is thinner. SW-S-SE aspects seemed to have better stability, especially at higher elevations.

Media

Advanced Information

Weather Summary

Wind:
Light , S

The Christmas night storm ended around 1400 on the afternoon of the 26th. Low lying clouds started clearing for the remainder of the day, and the 27th was a cold, clear, and relatively calm day at 7000'. Surface hoar had started to grow on the snow surface the evening of the 26th and continued for the next several days .

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Within the past week West facing Lower East Fork
W 6200' 		D2 SS I-New/Old Interface 6" N-Natural Start zone slope angle 38degrees.
2 Within the past week lower east fork
W 6200 		D2 SS I-New/Old Interface 6" N-Natural very similar characteristics to the other adjacent avalanche. Both had steep convex rollovers just above the crown.
1
None
1
None
1
None

My guess is that these ran during the peak intensity of the Christmas night storm. Bed surface was the Solstice Rain Crust, and the depth of the avalanche would have consisted of all of the snow since the Rain Event ended. There was about 3-4" of new snow on the debris

Snowpack Observations

At elevations below 8,000', on WNW through N through East aspects, we generally found a weak snowpack structure with consistent Propagation Saw Tests showing the likelihood of propagating cracks if a failure was initiated at the facet crust sandwich that is buried about 30" (70cm) from the surface. At elevations above 7,000', the slab that is present above this facet crust sandwich was mostly 1F hardness. At elevations below 7,000', the slab was not as cohesive, and had a hand hardness of 4F. Other tests confirmed our weak snowpack as columns would fall apart even before we finished cutting them. (see recent video observation). We used the information gathered from just walking around in boots to tell us where the weak snow was. When we sank up to our waists, we knew we were in a weak snowpack. Where we were not wallowing, we felt the stability was better as our weight was supported by the thicker SRC (mostly on SW-S-SE aspects above 7,000'). Surface hoar was observed around treeline and in drainage bottoms. By the afternoon of the 28th, a melt freeze crust had formed on exposed terrain of solar aspects.

Terrain Use

Assessment Mindset. We did not venture onto any slopes steeper than 30 degrees that were on the Northerly half of the compass. We utilized ridgelines and sub ridges slopes for ascents, and avoided terrain traps. There was really good riding on lower angle southerly facing slopes that had a supportive SRC.

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