| Recent Avalanches? | Yes |
| Collapsing (Whumphing)? | No |
| Cracking (Shooting cracks)? | Yes |
Observation: Turnagain
Location: Tincan
10:15-16:15
Toured through lower meadows below Tincan’s northwest shoulder and meandered onto the standard uptrack to a high point of 3,000’. We conducted instability tests, both at treeline and just above treeline, to assess recent wind effect and depth and distribution of current persistent weak layers. Our pit results showed moderate to hard strength, good structure and low propagation potential, due to lack of slab. However, once into the alpine while digging our second pit we witnessed a very small skier triggered slab. We investigated and found that failed it on the new/old snow interface (from the snow starting yesterday 2.9) of small surface hoar and near surface facets under a freshly formed 4″ slab. We also could easily triggered small slabs on a wind -loaded slope adjacent to the skin track near our high point. In this instance the slabs were slightly deeper and failing on the 1.28 bsh/nsf.
Low density surface conditions made for great turns, but also present plenty of snow available for transport with increasing winds.
Obvious signs of instability
Observer Comments
Localized cracking in isolated, exposed alpine ridges.
No collapsing observed.
Test slopes produced small releases of wind-loaded snow over the 1/28 surface hoar in the alpine on convexities.
Skier triggered small slab upper 2-4” of recent wind-stiffened snow over the just buried surface hoar and facets.
Minor sluffing
Weather
Overcast with intermittent periods of blue pockets over the heart of Turnagain by midday.
Light to moderate NE winds observed above 2,000’ with sporadic gusts after 13:00.
Significant increase in winds at 15:00 at 3,000’.
31°F at 1,000’ (10:15)
27°F at 1,915’ (12:30)
25°F at 2,400’ (14:00)
S-1 consistent throughout tour
Notably snowing harder near Portage on the drive both to the Pass and back to Girdwood.
Snow surface
1,000’ to 1,450’: 2-3” of new, low density snow over degrading melt-freeze crust from 1/23.
1,450’ to 2,000’: 2-3” of new, low density snow with wind skins present on exposed ridges over various layers of near-surface facets, surface hoar and soft settled snow.
2,000’-3,000’: 2-3” of new snow in wind sheltered areas and wind-stiffened surfaces on exposed slopes with low density snow below.
The 1/28 buried surface hoar layer is approximately 20-25cm below surface, at and above treeline.
Loose-dry is evident on most steep slopes and is reactive on convexities
Ski/Boot: 20-30cm / 40-65cm
Snowpack
Our focus was to assess the recent wind events in the upper snowpack and assess the depth, distribution and reactivity of the current persistent weak layers including the 1/28 buried surface hoar and near-surface faceting.
Instability tests at 1,915’ and 2,470’ specifically showed moderate to hard strength, a good right-side-up structure and low propagation potential, but lacked a slab.
Though small column tests showed the 1/28 buried surface hoar to be reactive with sudden collapse results when isolated, large column tests point to a lack of cohesion in the upper 20-25cm and therefore no slab was observed.
In terrain in the alpine that had seen more wind-loading and where a slab was forming we observed a small skier triggered that slid on the 2.9 interface of small facets and surface hoar. We also could easily get test slopes to slide on the 1.28 bsh and nsf.
Though winds did not manifest as forecasted, weather was deteriorating rapidly by 15:00. The onset of stronger gusts could produce the load that will tip the scales towards instability, especially with an abundance of low-density surface snow available for transport.
Pit #1: See Snowpilot
Pit #2: 2,470', S Aspect, 21° Slope, S-1, Light to Moderate NE winds
Tests:
CT15 SC 21 cm down on 1/28 SH
CT20 21 cm down on 1/28 SH
CT25 21 cm down on 1/28 SH
2xECTX
Snowpilot
Hardness Profile at 1.915'
ECTN8 23 down on 1/28 SH
4-6 mm 1/28 buried surface
Wind skin
NE wind filling in skintrack
Old cornice debris from CFR ridge
1.28 bsh @ 1910'
Small skier triggered slab
Looking down the small avalanche
Crown on a small test slope - weak layer 1.28 buried surface hoar and nsf
Cracking along a wind-loaded test slope