DonnerSummitAvalancheSeminars.com Professional, comprehensive avalanche safety education -- since 1998 – PO Box 83 Norden, California 95724 (530) 412-3585

Previous slide: Graupel, a heavily rimed precipitation form, is indicative of near-frontal precipitation, and has been a persistent weak layer in Donner Summit snowpacks. Rime ice, in it’s many manifestations, runs the gamut from fluffy cauliflower to bullet-hard water ice. Because of its aerosol scouring action, rime ice contains a very high concentration of acidic particles and typically has a pH significantly lower than rain or snow. Unless otherwise noted, all photographs in this slide show by Randall Osterhuber [email protected]

Donner Peak Raked with wet slab and loose snow releases, the north side of Donner Peak falls apart under heavy rainfall. February 23, 2009.

Zero/Zero The challenges “white out” conditions present in the mountains are numerous. Randall Osterhuber and Steve Reynaud skiing by Braille on the mid-mountain ice fields of Mt. Baker, Washington. Photograph by Dirk Schoonmaker.

Benson Hut On the Sierra crest about 7 km south of Donner Pass Unlike the other Sierra Club huts that sit astride snowed-over dirt roads, accessing the Benson Hut involves traveling through and around avalanche terrain. While most skiers approach it from Donner Summit—with the wind pounding the right side of their faces the whole way—more adventurous routes await from the south and east. But be forewarned: you will have to deal with steep snow—and the hut’s resident ghost.

Weather Watch Preceding the season’s first snowfall by less than an hour, lenticular clouds catch fire over a full moon and the Sierra crest in northern Yosemite.

Abies magnifica The incomparable red fir forests of Donner Summit rise up above 7 meter deep snowpacks. March 2011

Winter 1958 The snowpacks of April 1958 lay homage to a powerful snowfall season. Photograph from the archives of the Central Sierra Snow Laboratory.

A World of Snows Looking south over the Indian subcontinent from 6500 m elevation in the Himalaya.

O2 + C3H8

Position a pipe over an avalanche start zone, fill it with oxygen and propane—ignite.

POP! Gazex®, a remotely controlled avalanche mitigation system, above Nevada State Route 431, the Mt. Rose Highway.

Knee Deep Mikey Kennett plows the ski fields of the Carson Range, Nevada.

Springtime Stratigraphy Old surface crusts, and their concentrations of debris, stand out in the snow profile of April 24, 2008.

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April and May precipt (mm) Water Years 1971 - 2011

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Trend in springtime precipitation on Donner Summit

Alpine Meadows The aftermath of a large avalanche that destroyed the Summit building, and killed seven people, at Alpine Meadows, March 31, 1982. Photograph by Ken Menzer

Storm Slab Fragile layers are common within many Sierra Nevada snowfalls. Here, a soft slab releases on a subsurface weakness. Photograph by Andy Anderson

Picture this Turning our observations of the snow profile into cartoons has many advantages. We can quickly identify

weak layers, temperature anomalies, and failure planes. The software to produce these plots is free, at www.snowpilot.org

Kevin Bacon*

*Must appear in every slide show.

LiDAR Two images are combined from a LiDAR scanning infrared laser: one of the snow-free study site at the Central Sierra Snow Lab, and then the same scene under 1.8 m deep snowpacks. The snow surface of January 8, 2008 is isolated in superposition.

Comprehensive Decision Making in avalanche terrain must invoke many carefully weighed considerations—and acute observations.

Above Lake Tahoe’s north shore, February 2011.

Snow: not just about winter Ana Ting Jet Osterhuber descends the summer snowfields of Squaw Valley.

Near Piute Pass February 25, 2010 In the alpine, wind and sun are free to unleash their particular havoc.

Dew Point is the temperature at which a parcel of air becomes saturated and its water vapor condenses into a liquid (when dew point is > 0º C) or deposits into a solid (when dew point is < 0º C). Solid form deposition on the snow surface— surface hoar—crystallizes in many shapes and forms. Here, 4-5 mm surface hoar crystals from atop an early season Donner Summit snowpack.

Write it down Observers and measurers of the natural world—be it geologists, ornithologists, entomologists, or botanists—find great value and necessity in recording their field observations. As practitioners of snow stability, we do the same. Field notes help organize, communicate, and put into perspective the physics of the snowy world around us.

Gradient Sky A waxing gibbous moon hangs almost plumb over Mt. Adams, Washington.

The Ups and Downs Above the Norden train sheds, Donner Summit.

4 out of 5 Avalanche Activity? Yep. Heavy Precipitation? Oh yeah. Wind Loading? You betcha. Whumpfing, Cracking, or Collapsing? Duh! Rapid Warming? Ah, nope.

Snow v1.0.pdf

Rime ice, in it's many manifestations, runs the gamut from fluffy cauliflower to bullet-hard water ice. Because of its aerosol. scouring action, rime ice contains a ...

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