Observation: NWAC Forecaster
Basic Information
Observation Details
Observation Date:
February 9, 2023Submitted:
February 9, 2023Observer:
NWAC Forecaster - Matt PrimomoZone or Region:
East CentralLocation:
Upper IcicleSigns of Unstable Snow
Recent Avalanches?
YesCracking?
WidespreadCollapsing?
None ExperiencedMedia/Attachments
Advanced Information
Weather Summary
Cloud Cover:
Mostly CloudyWind:
Light , WNew/Recent Snowfall:
Found 30-40cm of new storm snow at mid and upper elevations, only 15cm or so at 4,000ft.Some sun poking through at times, but mostly cloudy. Wind driven plumes noticed on Grindstone Mtn and Hinman, though winds were calm to light in the area we traveled.
Avalanche Observations
| # | Date | Location | Size | Type | Bed Sfc | Depth | Trigger | Photos | Details |
|---|---|---|---|---|---|---|---|---|---|
| 1 |
Feb 9, 2023 () |
Upper Icicle E 6500ft |
D2 R2 |
SS-Soft Slab | I-New/Old Interface | 1ft |
AC-Cornice Drop c-Intentional |
|
Report
Link |
Numerous recent slabs off large N-SE facing terrain, up to D2.5 with crowns 30-60cm+ deep. Fractures were quite wide, sometimes encompass most of the terrain feature. A cornice kick easily triggered a large chunk of cornice, that triggered a ~100ft wide slab that was 30-45cm deep.
Snowpack Observations
We found sensitive conditions with the new snow as we gained elevation. Skin track tests would fracture at the new/old interface on steep slopes, down about 30cm on upper edge of Below Treeline band.
Cornice growth looked to be substantial over the past few days, and they were touchy today. Some exposed areas were wind affected, but many places were not.
Profile on N at 6040ft in sheltered open trees found an HS of 185cm. CTE Brk down 20cm on interstorm layer. CTM RP down 30cm, ECTN M here. CTM SP one time down 39cm, another time no results. ECTN M here as well. No results on MLK crust down 50cm, found as 0.5cm IFcr with 1F- rounding facets beneath.
Crown profile on intentionally triggered slab described above (E at 6,500ft) found the old/new snow interface as the bedsurface, which was a thin P- wind stiffened layer with DF's and a few faceted grains. The Feb 3 layer was only 4cm below and quite a bit weaker, with large rounding facets (2mm). The slide may have stepped down to this layer lower on the bedsurface but tough to tell for sure. I suspect some of the larger slides observed from higher features may have run on it. In any case, both of these layers seem slow to heal with the healthy load of new snow.
Avalanche Problems
| Problem | Location | Distribution | Sensitivity | Size | Comments |
|---|---|---|---|---|---|
Storm Slab
|
|
Layer Depth/Date: 30-40cm |
|||
Wind Slab
|
|
Layer Depth/Date: 30-80cm |
Loose dry avalanches were also running, though kind of sluggish. On very steep terrain they could gain some momentum though.