Date of Observation: 12/16/2021
Name: Evan Ross & Alex Banas

Zone: Northwest Mountains
Route Description: Slate River. NE, 9,000ft to 11,400ft

Observed avalanche activity: Yes
Avalanches: Nothing fresh since last weeks avalanche cycle. Of particular note, during the 12/10 avalanche cycle an avalanche had propagated from Run Away Ski, through the Lap Track Track Trees, and through most of Yogies. In my 14 or so years in this area I’ve only seen an avalanche go wall to wall across the lap track trees a few times. Cool or not cool?
Weather: Clear sky, becoming partly cloudy. Moderate wind gusts at ridge line transporting snow.
Snowpack: The Slate River Valley had plenty of wind-affected snow, but as soon as we started climbing into the avalanche paths out of the valley the snow surface was all lovely and unaffected by the wind event. Snow surfaces were soft even at ridgeline elevations. Ski pen around 25 to 30cm.

The snowpack in this area was greatly affected by the avalanche activity between 12/9 and 12/10. There wasn’t a lot of undisturbed snow out there. In those undisturbed areas, the persistent slab avalanche problem felt stubborn. We were able to get a few collapses, often with some extra effort.

On the slopes that had avalanche a week ago, I was eager to see if they were developing a new avalanche problem. Below treeline, I didn’t find anything concerning. Near treeline, there were some areas that did pose a concern due to the additional wind-loading.

Below treeline, I didn’t find anywhere that enough snow has accumulated on those old bed surfaces to create a new slab on the remaining facets. The average new snow depths on top of those old bed surfaces ranged from 30cm to 90cm. From a distance, it’s difficult to identify the slopes that avalanched on 12/9, while the slope that avalanche on 12/10 remained obvious.

Near treeline, the slopes that avalanched on 12/10, or generally later in the storm, didn’t pose much concern for a new avalanche problem on this tour. The slopes that avalanched early in the storm, around 12/9, were harder to identity that they had previously avalanched. Those slopes had seen enough wind-loading over the last week to start creating new slabs right near ridgeline. In the end, we didn’t avoid wind-loaded terrain, be we did make assessments and encountered heightened avalanche concerns in those areas.

Date of Observation: 12/16/2021
Name: Zach Guy

Zone: Northwest Mountains
Route Description: Views of Scarp Ridge, some of the Ruby Range, Axtell, and Gothic

Observed avalanche activity: Yes
Avalanches: Not much interesting to report. Looks like a pair of slabs on a leeward aspect off of Scarp Ridge.
Weather: Cold and clear, no wind transport.
Snowpack: We were wondering whether the extreme alpine wind speeds were actively loading the alpine or just blowing into space. From my vantage, northeasterly aspects got fatter in the past 24 hours. Some terrain features on other aspects definitely got stripped.

Date of Observation: 12/15/2021
Name: Zach Guy

Zone: Southeast Mountains
Route Description: CB Nordic Hill

Observed avalanche activity: Yes
Avalanches: Ski cut a small wind slab, 10″ thick, on a small, windloaded slope below treeline.
Weather: Winds actively blowing a few inches of new snow.

Date of Observation: 12/15/2021
Name: billy barr

Zone: Southeast Mountains
Route Description: Gothic townsite

Weather: A lot of noise but little substance. The wind gradually built overnight to become a full on blizzard around 5 a.m. But by 7 the wind has let up and the snow has, for now, stopped. There was just 1″ wind blown and warm snow with 0.10″ of water. A good bit of wind transport but not a lot of new snow to move. Currently overcast with light SW wind and light snow seems to just be starting. Overnight high ws 30F after yesterday’s high of 38F. The current and the low is 18F with 18″ of snow on the ground as it continues to settle.

Date of Observation: 12/14/2021
Name: Eric Murrow

Zone: Southeast Mountains
Route Description: West Brush Creek road to skin up Union Chutes. Terrain south of WSC Peak in West Brush drainage, directly across valley from Teocalli.

Observed avalanche activity: Yes
Avalanches: Noticeably less avalanche activity below treeline as compared to Northwest Mountains forecast area. Near treeline produced numerous avalanches on north and northeast aspects directly below ridgeline in wind-drifted areas on shaded aspects.
Weather: Broken skies for much of the day with a pleasant period of Few clouds around 2 pm. Winds were light below treeline and looked to be moderate at ridgetop, but no wind loading was observed.
Snowpack: Small Surface Hoar was present near valley bottom but 100 feet above cold sink Surface Hoar disappeared. Snow surface on shaded aspects near and below treeline was faceted but small-grained (.5mm). Around 11,000 feet and above soft, breaker wind-board appeared across the landscape. I experienced many localized collapses, but just a single, loud moderately sized collapse as I exited a northeast-facing profile site (see attached image) which produced many cracks across the slope. I avoided steep, wind-drifted terrain in the area and stuck to simple, lower-angled options.

Snow depth on sunny slopes in the area was around 35cm and 70cm on shaded slopes. Ski penetration was generally around 6-8 inches and boot penetration was to the ground everywhere.

Photos:

Date of Observation: 12/13/2021
Name: Zach Guy

Zone: Northwest Mountains
Route Description: Various aspects near Kebler Pass and Lake Irwin.

Observed avalanche activity: Yes
Avalanches: Nothing new. Documented a few older slides from the past cycle.
Weather: Few clouds. Moderate southwest winds at ridgetop with some light transport at times.
Snowpack: Primary goal today was to test the sensitivity of the persistent slab problem on shady aspects. Although it’s getting harder to produce signs of instability than earlier this week, the snowpack is still talking. I skinned over, then jumped with skis on, and then post-holed into four suspect low-angle slopes below treeline. One slope remained quiet, one produced a localized collapse when I skinned over a shallow, wind eroded feature, and two of them produced rumbling collapses after I stepped out of skis and sunk my boot into the weak layer. Slab depths in this area were 75 to 80 cm to the 12/6 facet layer.
Also dug into a southerly aspect near treeline to test bonding to the 12/6 crust. No alarming results and no signs of instability while traveling on southerly aspects.

Surface hoar growth observed below treeline.

Date of Observation: 12/12/2021
Name: Irwin Guides

Zone: Northwest Mountains
Route Description: Thornton’s Glade

Observed avalanche activity: Yes
Avalanches: SS-ASc-R2/D2-G 70-100cm x 10-20m x 100m running on moist basal FC. West aspect NTL.
Triggered on an ~36 deg planar slope that harbored a nice swath of pre-12/6 FC.

Date of Observation: 12/12/2021

Zone: Northwest Mountains
Route Description: Camo Glades

Observed avalanche activity: Yes
Avalanches: Large slab in an opening in the trees ran a few days ago.

Date of Observation: 12/11/2021
Name: Ben Pritchett

Zone: Northwest Mountains
Route Description: Ruby Range and Whetstone as viewed from town

Observed avalanche activity: Yes

Date of Observation: 12/12/2021
Name: Zach Guy

Zone: Southeast/Northwest Mountains boundary
Route Description: Mount Emmons. Traveled mostly on S and SE aspects to 12,400′

Observed avalanche activity: Yes
Avalanches: Adding a pile of previously undocumented naturals to the list from the recent cycle that fit the pattern of what we’ve been observing, see photos and details below. Most of the northeast side of Red Lady Bowl appeared to run and there were a handful of wind slabs that ran on the southeast portion of the bowl. I didn’t see any fresh avalanches from the past 24 hours.
Weather: Sunny, clear. Winds were strong enough to blow my #tired hat off my head, but luckily I retrieved it. Snow transport continues above treeline in exposed locations.
Snowpack: Our field objective today was to assess if the persistent slab problem should expand to the sunny aspects that held a crust (rather than dirt) before the storm. In short, I didn’t find evidence of persisting issues on the 12/6 crust where it is stout on sunny aspects. In a pit on a SE aspect NTL, long column tests produced no concerning results on the crust. The crust is pencil hard and goes to the ground where we dug. Above the crust, there are .3 to .5 mm rounding facets, 4F- (the 12/8 layer).
We traveled mostly on sunny slopes that were dirt before the storm with no signs of instability. As soon as we scooted into some low angle, shady terrain below treeline, we started getting collapses that would radiate to the nearest cluster of trees. These same slopes are developing small grained surface hoar and near-surface facets on the snow surface right now. Kicked at a few recent drifts at higher elevations with minimal cracking.