Sunday, January 16, 2011

Pilot Peak - January 15th 2011

Yesterday was Pedro's last day of Idaho Skiing for this season before his return to Berkeley. We were concern that the snow conditions were going to be "uncooperative" and that skiing was going to be highly instructional. Man, were we wrong! Skiing at Pilot Peak was much better than we expected. The snow was heavy but creamy. The top 20 cm  were soft (fist hard), and if you were gentle on the skis and skied long arcs at speed, skiing was a lot of fun. The trick was to keep the skis floating in top 20 cm of snow. But if you allow your riding tools to sink ... well it was not hard to end up doing face plants.

In many places above 6500 feet of elevation the new 35-45 cm of snow is resting at N, NE, E aspects above a layer of "surface hoar" crystals. This layer was sensitive today with numerous massive "whumpfs". Interesting enough we did not detected surface cracks during the multiple collapses (whumpfs).

Stability assessment at N, NE, E aspects between 7000-7700 feet revealed easy triggering and propagation likelihood:

  • Multiple CT1Q1 (SC) at 45 cm (SH 4-5 mm)
  • ECTPQ1 SC at 45 cm (SH 4-5 mm)
  • PST 40/100 (End) at 45 cm (SH 4-5 mm)
  • More than a dozen of Easy Hand tests at N, NE, E aspects elevation 7000-7700 feet. Some of the Hand Test failed during isolation in pockets with very well developed surface hoar crystals, and easily slided downhill!
The term SC above refers to the collapse of the slab above the weak layer during the test. The SH term denotes a surface hoar weak layer with large crystals in the 4-5 mm range.

Observations and testing at SE aspects did not reveal instabilities present and the buried surface hoar was NOT detected. We choose to threat these slopes as suspected and keept angles below the 32 degrees of steepness, limiting our mobility (switching to the Glades Ridges) when skiing the SE aspect slopes of the long and fun Knob ridge.

The ECT (Extended Column Test) ans PST (Propagation Saw Test) are tests that allow us to gain understating on the propagation potential of fractures. You will find descriptions for this tests at the following link:

Another party reported RB2-Q3 at a slope with East aspect at 7900 feet.

Two natural release were observed by our party at a NNE slope with 34-36 slope angle at the starting zone. They were classified as SS-N-D1.5-R3-N and ran for 100 vertical feet.
  • SS means soft slab
  • N stands for natural release
  • D1 describes destructive power, a one suggest that ran less than 10 meters. A D2 can bury a skier.
  • R3 quantifies the distance it ran, for an scale of R1 to R5, with R5 as maximum.
  • The second N denotes that the avalanche involved NEW snow.
If you are interested in reviewing and/or familiarizing with the classification and recording of avalanche observations please refer to the following link:

Yesterday was easy to find instabilities in the snowpack at Pilot Peak. The obvios red flags were: collapses, warming temperature trend, and recent loading event (45 cm of NEW snow). To this list we can possibly add ratings of considerable or above on the the regional forecasts (HIGH for Payette Forest and West Mountains, and Considerable for the Sawtooths).

It was comforting to observe all parties exercising good judgement and managing angles during yesterday ski outing. Surface Hoar instabilities are notorious for avalanches getting triggered at shallower angles (lower 30's), and as far as I could tell skiers and riders were skiing terrain that did not exceeded 30 degrees in steepness.

Todays's forecasted rain up to 8000 feet, and continued warm temperatures above the freezing level will make skiing less attractive (Movie Theater Time!), but in the meantime it is likely that in the long term it will assist in stabilizing the snowpack.

Chago & Pedro