Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
March 15, 2023
Submitted:
March 16, 2023
Observer:
NWAC Forecaster - Andy Harrington
Zone or Region:
West South
Location:
East Peak + Cement and Lakes Basins

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
None Experienced

Media/Attachments

Out skin track near a ridgeline drifted in between laps.
Cornices have grown very large in many locations.
A human-triggered avalanche on a steep convex slope that ran far and fast on an underlying sun crust.
Signs of wind on a reverse aspect than the typical loading pattern.
Shovel tilt test highlighting some instabilities from this week's storms.
Snowpit on a northerly aspect. Weak snow was found at the 3/12 interface.

Advanced Information

Weather Summary

New/Recent Snowfall:
4-5" HN24; ~ 1 foot over the 3/14

Mostly cloudy with short periods of sun breaks. The winds were moderate and cold near ridgelines

I triggered a D1 loose avalanche on a convexity that involved the HN24. A few very small (<D1) natural loose avalanches were spotted on solars. A few older slabs were buried under a few inches.

Snowpack Observations

Traveled up East Peak before heading down into Cement and over into Lakes Basin looking at terrain and for recent avalanche activity.

Conditions are somewhat aspect and elevation-dependent:
Below ~4000 feet: Rain from 3/13 affected the surface and has now locked up - creating a firmer base. The HN24 of 5 inches plus a few inches from the cooldown on Monday sits atop the crust.

Above ~4000 feet: Cold dry snow with plenty of recent wind effect exists. Wind press, Wind Slab, textured surfaces, sastrugi, large cornices, fresh drifts, and actively blowing snow were all observed throughout the day. Most slabs were found near ridgelines, on convex rollovers, or the sides of gullies. There was enough visible wind effect to keep us out of terrain we had previously thought of skiing. Winds were actively reverse-loading near ridgelines.

On Slopes that see direct sunshine: A sun crust formed on 3/14, bisecting this week's storm snow. It was on this crust that I was able to trigger avalanches in the new snow that ran far and fast on convex slopes. At the end of the day, a new sun crust was again forming on the surface.

On shaded slopes: Layered cold dry snow exists with storm interfaces identified through small column tests. Digging on a northerly aspect, I received hard compression test results on the 3/14 interface (down 28cm). Possibly more concerning going forward is likely the 3/12 interface (down 53cm) where I received planar and sudden results during small column tests. These typically failed just outside of normal bounds (+1) and were found to have failed on near-surface facets mixed with surface hoar fragments


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