Avalanche Advisory for 2016-01-17 07:03:37

We have an abundance of information from the field yesterday coming from multiple locations in our forecast area.  Snow conditions and observations run the gamut ranging from "right side up" snow layer structure to "upside down", wind loaded slopes, cornices, soft storm slabs, natural and human triggered avlanches.  First, allow me to tell you what I found on Mt. Shasta just above treeline (8,200 ft), along the edge of Green Butte ridge as it drops into lower Sun Bowl, southeast aspect.  

A snow study pit dug at that location revealed obvious wind loading with some weakness in the bonding of higher density wind deposited snow sitting on top of slightly less dense wind deposited snow. All this sat on top of the widespread rain crust.  I was surprised to find evidence of the rain crust at 8,200 ft., but it was there.  An extended column test resulted in a score of ECTN 14 Q2 with a fracture depth of 31 cm.  A shovel shear test was performed  and easy to moderate failures occured at 11 cm deep, and again at 31 cm deep, as previously indicated.  Keep in mind that the shovel shear test only indicates the location of weaker bonding.  The sensitivity of wind slabs, in the various locations they exist, remains uncertain.  The ferocity of this storm will keep folks from wandering into areas above treeline where wind slabs mostly exist, however wind deposited snow and cornices exist near treeline, as well.  Avalanche danger associated with wind slabs will increase with today's storm and the accompanying high winds.

Second, the Castle Lake area remained active yesterday with two separate avalanches occurring; one naturally triggered and one skier triggered, both on Left Peak. I will present the details bullet point style:

• 1/16/2016-stormy and windy
• Skier triggered soft slab along convexity of steep rollover around rocky outcropping
• 18-20 inch crown at deepest point, and approximately 50 ft. in width
• Slide stepped down to a deeper weak layer in areas
• 2 weak layers noted above rain crust layer. One approximately 20 cm deep and one about 30 cm deep
• Perhaps a density change in snowpack, or small faceting taking place due to steep temperature gradient ABOVE rain crust
• One naturally triggered avalanche near ridge top on Left Peak caused by cornice collapse and subsequent trigger of soft storm slab above rain crust on slope beneath

There were also reports given from the northerly aspect of Right Peak where shooting cracks, and stiff slabs of heavier snow over lighter density snow exist.

At the forefront regarding avalanche danger is the impressive amount of water forecasted to fall over the area during the next 48 hours.  Further, rising temperatures will give way to rising snow levels and rain on snow below treeline. Wet-loose related snow instabilities should be on your mind. Roller balls are relatively harmless, however we've got 1-2 feet of new snow sitting on top of our 1-2 cm thick rain crust... Add heavy, wet snow and/or rain on snow and we could see wet-loose/wet slab type avalanches. Rain only adds weight to the snowpack, not strength. Any wet-loose/wet slab instability due to rain on snow will be immediate. Areas up to about 7,000 feet could get rain on snow. Elevations above 7,000 will see snow, albeit heavy snow. 

Travel well spaced and one at a time through known avalanche paths and runout zones.  Have good, open communication with your travel partners, choose your route conservatively and pay close attention to the snowpack and terrain. Avoid wind loaded, open slopes 35 degrees and steeper near and above treeline.  

Quick Pit from 1/16/2016  @ 8,200 ft on a SE aspect, lower edge of Sun Bowl by Jon Dove:

Cracking of wind slab under skis along wind loaded edge of Sun Bowl, 1/16/2016-photo: Jon Dove

Skier triggered soft slab avalanche along steep roll over, N aspect Left Peak, Castle Lake on 1/16/2016:

Previous pit profiles 1/14-15/2016. Note the temperature gradient around rain crust in 1/14 profile from Left Peak:

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LOCAL AREA ROAD, NORDIC and SNOWMOBILE PARK STATUS:

The Sand Flat cross country ski trails are in great shape and ready for your cross country skis or snow shoes. These are backcountry trails marked with blue diamonds on trees. Trails are not groomed.  Snow shoers, please blaze a parallel trail to cross country skiers staying out of the skin track. These trails can be accessed via the Everett Memorial Highway. Thank you, and enjoy!

The Mt Shasta Nordic Center is open! These beautiful, groomed trails can be accessed via the Ski Park Highway. http://www.mtshastanordic.org

The Pilgrim Creek & Deer Mountain Snowmobile Parks are open! Trails are being groomed currently. Head to our "Education" tab on our website and find the snowmobile section for trail information, grooming status and other sledder resources!

The Castle Lake road is plowed to the Vista Point. The Everett Memorial Highway is plowed to Bunny Flat.

The Five Red Flags of Avalanche Danger any time of year include:  1) Recent/current avalanche activity  2) Whumphing sounds or shooting cracks  3) Recent/current heavy snowfall  4) Strong winds transporting snow  5) Rapid warming or rain on snow.