Observation: NWAC Forecaster

All Observations

Basic Information

Observation Date:

February 18, 2023

Submitted:

February 18, 2023

Observer:

NWAC Forecaster - Dallas Glass

Zone or Region:

Snoqualmie Pass

Location:

Cave Ridge, Commonwealth Basin (All Aspects Near Treeline E-S-W Below Treeline)

Recent Avalanches?

Yes

Cracking?

Isolated

Collapsing?

None Experienced

Classic signs of wind loading were found on NE-SE aspects above 4800ft.

An intentionally triggered wind slab avalanche right where all the clues indicated it would be. NE, 5300ft, HS-ASc-D1-R3-I

A snowprofile near treeline on Cave Ridge.

This shovel tilt test easily highlighted the 2/17 interface.

This 12ft long shooting crack occured in wind loaded terrain. In this case the slope wasn't steep enough to avalanche.

Rollerballs on were sound and triggered on steep slopes at lower elevations.

Advanced Information

Cloud Cover:

Obscured

Wind:

Moderate , NW

New/Recent Snowfall:

4-6in (10-15cm)

Warm and damp down low with snow still clinging on at Pass level around noon. Up higher, rather stormy with moderate winds, blowing snow, and colder temperatures.

Avalanche Observation Comments:

I was able to trigger a few small wind slabs on test slopes near the top of Cave Ridge. Crowns were 6-12" deep and some of them propigated widely across the relatively small features.

Tale of two snowpacks.
Above ~4800ft: About 15-18in of snow sits over the 2/13 crust. In general, the upper snowpack was right-side-up and did not indicate any obvious weak layers. The 2/17 interface was marked by a crust on southerly aspects. In a few places, strong winds had scoured the snow down to this crust. On shaded slopes, the 2/17 interface is more subtle. Snow grain ID was difficult today with the blowing snow, but I did not find buried surface hoar in my snow profiles and hand pits.
Wind Effect: As soon as I crested out of the thick trees, wind-affected snow observations were easy to find. Blowing snow, drifts, cornices, textured surfaces, scoured slopes, etc. Several drifts and small test slopes produced cracks (up to 12ft long) and occasionally small avalanches. Wind slabs were generally 4-12 in deep.
Below ~4800ft: The snowpack down lower was much heavier and wetter. Rollerballs were prevalent on many steep slopes. The upper snowpack above the 2/13 crust is more condensed and stronger. I did not find any significant weaklayers at these lower elevations.

Problem	Location	Distribution	Sensitivity	Size	Comments
Wind Slab	N E S W	Isolated Specific Widespread		D1 D1.5 D2 D2.5 D3 D3.5 D4 D4.5 D5

WordPress Lightbox