Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
January 20, 2023
Submitted:
January 20, 2023
Observer:
NWAC Forecaster - Andy Harrington
Zone or Region:
Snoqualmie Pass
Location:
Chair Peak - North Slope - Cache Couloir

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
None Experienced

Media/Attachments

A natural avalanche was witnessed in the morning hours. This may have started as a loose coming off the sun exposed upper slopes or from a small cornice fall. It triggered a small slab as it descended, leaving behind a crown just below the confined gully. [E 6000']
Actively blowing snow off ridgelines were observerd on 1/20. The snow was likely sifting in to the base of the cliffs, building Wind Slabs.
A small skier triggered wind pocket on a convexity. Note the slightly textured surface.
Wet Loose activity due to the sun helping shed snow from rocks. [S 5300']
Weak surfaces were observed on shady slopes in the Alpental Valley on 1/20.

Advanced Information

Weather Summary

New/Recent Snowfall:
No new snow

Beautiful sunny day at the pass with some light winds high on the ridgetops

At 9:45 we witnessed a natural avalanche coming out of the Upper Chair Peak Basin. Its trigger is not known - could have been a small cornice failure or snow shedding from the sun-exposed slopes of Chair Peak. As it descended and exited a gully, it triggered a small slab and ran a couple of hundred feet.
There was also lots of natural wet loose activity around the valley, with at least one sizeable slide almost hitting ski tourers near the Thumbtack during the late morning hours. Other small wet loose avalanches were observed as I exited toward the parking lot and as I drove home.

Snowpack Observations

There were a plethora of avalanche professionals in the Alpental Valley on Friday, some working and some out playing in the nice weather. Talking with many of them, the story remained consistent. The snow settled quite a bit between Thursday and Friday, the sun was strong and impacting the surface, resulting in small wet avalanches, and shady slopes held cold dry snow with weak surfaces on top. I was a bit surprised to see actively blowing snow off the ridgelines, helping to continue to sift snow into deeper piles. I triggered a small pocket of wind effected snow as I descended a steeper convexity. Another avalanche professional in the area relayed that some stiff wind slabs were enough for him to alter his travel plans that day.

While not many folks were digging to look at deeper layers, I took a moment on the North Slope of Chair Peak [N ~5000'] to get some information about how much snow was over the MLK crust and if there were any deeper layers of concern heading into this next round of precipitation. I found just under 100" (250cm) height of snow with 22" (55cm) over the MLK crust. When investigating the 1/18 layer that was highlighted in snowpack tests the day prior, I found somewhat similar test results, but no needle-like grains as I had the day before on Snow Lake Divide.

While there may be some layers of interest that could cause issues, the number of people out skiing (some skiing extreme terrain) on Friday with no known reported avalanches has me less concerned about these layers moving forward. That said, they do continue to show up in the same place (10-15cm above the MLK) and break consistently CT+1 (or 2) and are highlighted in tilt tests.

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