Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
December 27, 2022
Submitted:
December 27, 2022
Observer:
NWAC Forecaster - Josh Hirshberg
Zone or Region:
East North
Location:
Cutthroat creek (E-SE, 2,200-6,000ft)

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
None Experienced
Collapsing? 
Isolated

Media/Attachments

A mid-storm interface producing easy, planar shears 1ft below the surface. Cutthroat ck, ESE, 5340ft
A profile showing 46cm of new snow over the 12/25 crust and melt forms. The 12/8 surface hoar produced test results indicating potential for propagation, despite the hard, overlying snow.
Results from a propagation saw test indicating that, if initiated, propagation is likely on surface hoar (12/8?). It's now capped with a stout layer of melt forms.
Large, 1cm, surface hoar (12/8?) found about 3 ft below the the surface. Cutthroat ck, SE, 5340ft
Profile from Cutthroat creek, ESE, 5340ft. 46cm on the 12/25 crust. Notable test results showing propagation on buried surface hoar.
https://youtu.be/LkqCDCocKys

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Temperature:
29°F
Wind:
Light , NE
New/Recent Snowfall:
>4,000ft- HST 40-45cm. 2,000ft, near Mazama- HST 27cm. In past 24-36hrs

Just sub-freezing temps, Light, S1 to S-1, snowfall throughout the day. Surprisingly deep accumulation since the night of the 25th. Recent snow has been warm and moist, tho certainly snow. Mostly calm, with light breeze at near treeline ridge. Visibility limited observations. Faint views of the top of Vasiliki Ridge and high ridges on Hinkhouse Peak.

No avalanches observed. Only saw small percentage of nearby terrain.

Snowpack Observations

The most recent crust (likely buried night of 12/25) is now down 40-45cm in the Cutthroat creek area. Overlying new snow is well-bonded to it. We experience 1-2 isolated collapses while on snowmobiles that may've been under the crust.
In the valley, up to at least 4,000ft, the crust was a 5-10mm thick, clear ice lens. Between 4,400-5,200ft it transitioned to a softer, thicker layer of melt forms capped with a very thin, pencil-hard crust.

A profile at 5,340ft, SSE with height of snow of 161cm revealed 46cm of "right-side up" storm snow, getting progressively harder and moist near the crust. Tilt and compression tests showed easy, planar, progressive compression, failures in the middle of the storm snow @ 130cm. I expect these to bond quickly. No test results on 12/25 crust. Other notable observations include:
-A mostly moist upper and middle snowpack, well-below 12/25 interface.
-Surface hoar (7-10mm, 12/8?) @ 56cm, intact and dry, produced multiple test results indicating potential for propagation (CTH (SC), PST 30/105 END).
-No results in lower snowpack (incl mid-Nov layer).

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Storm Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Weak Layer(s): Dec 25, 2022 (MF)
Comments: Quickly becoming a non-issue
Wet Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Weak Layer(s): Dec 25, 2022 (MF) Dec 8, 2022 (SH)
Comments: While 12/25 melt forms were generally strong and showed few signs of instability, the underlying surface hoar (12/8?) has become more reactive with the new load. It may be difficult to affect the SH through the new crust and slowly freezing melt forms. As observed today, it's possible that a snowmobile could trigger the layer by digging through the upper snowpack. This could change as the melt forms freeze.