White Wing: Thawing and Wind Transport

Submission Info
Saturday, February 10, 2018 - 12:00pm
Red Flags: 
Recent loading by new snow, wind, or rain
37° 43' 57.72" N, 119° 2' 37.68" W
Snowpit Observations
More detailed information about the snowpack: 

Had quite the little adventure trying to go up White Wing from the bottom today. We figured that the road would be driveable to near Obsidian Dome at least, but 4 wheel drive was was no match for the sheet ice covering everything so we parked at the Hartley Springs turn off and walked. There was just enough snow to put skis on at 8250', at least on N aspects, so we crossed the creek (which is exposed most of the way up now) and skinned up the E aspect lower reaches of White Wing to the bottom of the E face. Snow depth averaged about 30cm and the general structure was a thick (10cm) melt-freeze crust on top of dry small faceted grains on top of another thin but very hard melt-freeze crust on top of large facets to the ground. The ground in many places has an ice crust under the lowest facet layer. Snow on E and SE aspects was already well on the way to thawing by 9am. Two sets of field weather observations to quantify the warming and see if lower elevation NE aspects were transitioning to melt-freeze yet. Site 1 was at 8640' on a NE aspect at 1010am: Tair = 7.5 deg C, Tsurf = 0 deg C, T-20 = -1 deg C, Ski pen = 5cm, Boot pen = 20cm, Snow depth = 20cm, Wind = light from the W with moderate gusts, Sky = scattered clouds. Site 2 was at 9710' on an E aspect at 11am: Tair = 6 deg C, Tsurf = 0 deg C, T-20 = not observed, Boot pen = 5cm, Snow depth = 15cm, Wind = light from the W (this was a sheltered area), Sky = broken clouds. Winds above site 2 were consistently moderate from the W. Blowing snow was observed in saltation and turbulent suspension above treeline on NE and E aspects (see video). Toured/walked along the top of the ridge to look at N aspects. Thanks to the wind, what had previously been soft surface facets was now hard sastrugi and breakable wind crust (see sastrugi photo). Some small and localized cracking around our skis. We decided to ski the E aspect hoping to hit the tail end of good corn rather than wrestle with sastrugi around 1145am, but we were a little late and ski penetration was already almost full snow depth (~15cm) and the wind was already re-freezing the surface making for "crusty corn".

New wind loading today was noteable, winds probably kept slopes cool enough for too many wet instabilities. Our biggest worries today however were treacherous skiing conditions, many obstacles (see coverage photo), and driving conditions. We got down just before a low deck of clouds/fog blew in, but there was no precip accompanying it, at least where we were.

Snowpack photos: 
Coverage on E aspects
Sastrugi and breakable wind crust on N aspects
Snowpit videos (tests, etc): 
Weather Observations
Blowing Snow: 
Air temperature: 
Wind Speed: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 

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