Wind loading on leeward slopes above treeline.
Observation: Turnagain
Location: Tincan
Ascended Tincan veering slightly southwest off the standard uptrack and descended the trees. Our focus for the day was to investigate how surface conditions were changing with the storm rolling in. Above treeline the wind was moderate, gusting to strong, with wind actively loading leeward areas. During our tour it snowed lightly on and off, accumulating an inch in spots. Skiing conditions were really quite good, with soft conditions all the way down from our highpoint at ~2500 ft.
Observer Comments
Weather
1100, Tincan Pullout: 23 degrees F, wind NE calm to light, snowing lightly, sky obscured
1400, 2500' ridge below Common: 16 degrees F, wind ENE moderate to strong, snowing ~1 cm/hour, sky overcast to obscured
1500, Tincan Pullout: 26 degrees F, wind N calm to light, NO precip, sky overcast to obscured
Snow surface
Trace to 1" of new snow had fallen during our tour over surface hoar from 3 mm to 2 cm in size (decreasing in size with increasing elevation). Above treeline soft wind slabs were beginning to form in leeward areas. The surface hoar was still standing during our tour below treeline, and was knocked over in some areas above treeline due to the winds. The surface hoar is on top of near surface facets sitting over hard wind slabs or melt freeze crusts above treeline.
Snowpack
We dug several pits at 2500 ft on a SW aspect on a 35-37 degree slope. A pit located in a wind loaded area resulted in a CT 15 Q3 down 25 cm in a layer of 0.5-1 mm facets sandwiched between two melt freeze crusts. The same layer failed in a wind scoured area at CT15 Q3. The height of snow was 120 cm to 140 cm on the slope we dug. Of note, the snowpack has dried out quite a bit, 3mm surface hoar was found intact under the new snow and recently wind loaded snow, and the 2mm Thanksgiving facets near the base of the pack were quite compressed and P+ hard.
Pit at 2500' on Tincan
Windy and stormy conditions on Tincan Ridge
New snow falling on weak snow at 2500'
Visibility dropping quickly as the storm rolls in
Stormy snow study on Tincan
Intact surface hoar perched atop near surface facets below treeline