Professional Observation
Basic Information
Observation Details
Observation Date:
December 31, 2020 - January 3, 2021Submitted:
January 4, 2021Observer:
WAC - Killian Sump Caleb MerrillZone or Region:
Southern WallowasLocation:
Norway BasinSigns of Unstable Snow
Recent Avalanches?
YesCracking?
WidespreadCollapsing?
IsolatedSnow Stability
Stability Rating:
PoorConfidence in Rating:
ModerateStability Trend:
WorseningBottom Line
Our bottom line is that in the Southern Wallowas we have a very weak snowpack structure, with defined weak layers and a slab above, the perfect ingredients for a big avalanche. As more weight (3.6 in SWE in 5 days) was added to the snowpack, those persistent weak layers have become even more stressed, not to mention the storm slabs that came along with those precip events. Overall, the snowpack near treeline seemed to be the most complex. Careful snowpack assessment and terrain selection is critical at this time.
To recap, from Wednesday 12/30/20 to Sunday 1/3/21 at 7,000', we received 36" (90cm) of new snow with a snow water equivalent of 3.6" (91mm). Moderate winds out of the Southwest transported new snow into shallow wind slabs in leeward terrain. As the storm on 1/2/21 cleared, the winds shifted to the north also bringing a break in the storm during the day of 1/3/21. Avalanche hazard rose during the peak intensities of this storm cycle, and numerous natural storm slab and dry loose avalanches were observed on most aspects at most elevation bands.
Advanced Information
Weather Summary
Cloud Cover:
OvercastThe Southern Wallowas are currently (Monday 01/04) receiving what is sure to be another heavy load of precipitation and wind.
Avalanche Observations
| # | Date | Location | Size | Type | Bed Sfc | Depth | Trigger | Comments | Photo |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Past 48 hours |
Norway Basin W 7000' |
D1.5 | SS | S-New Snow | 1 foot | N-Natural | Natural avalanche on a steep convexity with a slope angle of 37 degrees. Avalanche ran within the new storm slab on an interface of a slight rime/freezing fog crust with graupel snow below crust. 200 feet wide running 100 linear feet |
|
| 2 | Past 48 hours |
Cornucopia Road W 4000' |
D1 | O-Old Snow | 2 feet | N-Natural | Road Bank Avalanche |
|
|
| 20 | Past 48 hours |
Pine Creek Drainage Up to 8500' |
D1.5 | SS | I-New/Old Interface | 1 foot | N-Natural | Numerous small natural avalanches noted on most aspects below 8500'. Did not notice any of these avalanches stepping down into older snow. |
|
Most avalanches crowns observed were between 1 and 2 feet deep (30-60cm)
Snowpack Observations
On Friday, we dug a pit on a WSW aspect at 7,000 ft. In general, we got moderate failures on the Solstice Rain Crust and the Old November Facets. Here were our results from that pit:
CT22 BRK down 55 (SOLSTICE RAIN CRUST)
CT27 SC down 100 (OLD NOVEMBER FACETS)
ECTN17 down 30 (I/O)
PST35/100 END down 100 (ONF)
On Saturday, we dug on an East aspect at 6,900 ft. In general, we found a very reactive snowpack with propagation propensity, with tests failing easily on both the Solstice Rain Crust and the Old November Facets. This pit is documented on SnowPilot and graphed below. Here are our results from that pit:
CT3 RP down 19
CT3 SC down 70 (SRC)
ECTP21 down 75 (SRC)
PST40/100 down 75 on 20202212
PST30/100 down 95 on 20201312
Avalanche Problems
| Problem | Location | Distribution | Sensitivity | Size | Comments |
|---|---|---|---|---|---|
Storm Slab
|
|
Layer Depth/Date: up to 2 feet deep |
|||
Persistent Slab
|
|
Layer Depth/Date: 3-4 feet deep on Old November Facets |
|||
Wet Slab
|
|
Layer Depth/Date: 3 feet More likely below 6500' |
There is a high likelihood of small soft slab releases based on what we saw. We have a Persistent Slab problem that may be less likely to trigger, but could be large and devastating avalanches. There is wind slab potential up near ridges on leeward slopes.
Terrain Use
We managed the Considerable to High avalanche danger by staying on lower angle slopes and mostly skiing in non-avalanche terrain. Our mindset became more conservative as we got more snow and dug more pits.
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