Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
February 12, 2023
Submitted:
February 12, 2023
Observer:
NWAC Forecaster - Andy Harrington
Zone or Region:
Snoqualmie Pass
Location:
Chair Peak

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
None Experienced

Media/Attachments

Recent avalanche activity from this week in the Alpental Valley. Older slabs and newer loose avalanches.
Rollerballs were present on most sun-exposed slopes and even some shady ones.
Large double crown in the Upper Chair Peak basin. This slide occurred earlier this week during a rapid loading event.
The snowpack is now too deep for probes, so we need to measure from the top down. Overall the snowpack is generally right-side-up over the 2/3 interface with a few layers to watch.

Advanced Information

Weather Summary

New/Recent Snowfall:
No new snow

Beautiful blue skies, little to no wind, and unseasonably warm this morning. Clouds rolled in mid-morning and by noon it was grey and a bit breezier. Still plenty warm enough, though.

Saw plenty of recent Wet Loose avalanches from the last 48 hours, but didn't seem to find many that occurred today. If the sunshine had continued, we may have gotten there. I was out of the field by 12:30, maybe something happened after that.

Snowpack Observations

I traveled up the Alpental Valley and ascended Chair Peak fan past the Thumbtack to the North Slope. Took a few laps down to the natural bench above the cliffs before descending the North Slope proper down to the Lake. Traveled across the lake, before heading up and over the divide back to the car around 12:30.

As expected, any slope that saw direct sunshine the past 2 days had plenty of signs of solar input - rollerballs, pinwheels, Wet Loose avalanche debris, firmer "frozen" snow first thing in the morning, and wetter/stickier snow as the sun once again softened the surface. Not much else to report in these areas.

On shadier slopes at upper elevations, we found surface hoar and colder, drier snow. The first lap was powder-like and skied extremely well. As we came up for a second, the snow was already getting warmer and wetter on the surface, even on the northerlies. They did not fully reach the point of producing wet avalanche activity, but it did help to knock the surface hoar down. I suspect in more protected shady areas, it held drier snow for longer, but the temps probably got to most spots today. As we descended to the lake, the snow got progressively heavier and wetter.

Dug a quick pit [N 4850'] to look at the upper snowpack above the 2/3 interface, which I believe was ~3.5 feet below the surface. There's roughly 4 inches of snow above the wind-stiffened 2/9 interface. About a foot below the surface I found a graupel layer that showed up in small column tests and tilt tests. And about a foot and a half below the surface I got repeatable hard results in compression tests and shovel shear tests. No layers propagated during an ECT.

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