Avalanche Advisory for 2016-02-21 06:54:00

Observations were made, and collected from multiple locations yesterday.  I made a ski tour at Castle Lake that revealed relatively stable conditions with only isolated wind slab formations along the ridge top, nestled in leeward pockets around steep, rock formations.  Some loose dry surface sloughing was witnessed in steep terrain over 37 degrees on shaded northerly aspects. Snowpack conditions reported from a volunteer field observer who made a ski tour up Green Butte ridge to Powder Bowl on Mt. Shasta dug a snow study pit at 8,200 ft. on a WNW aspect that falls into Avalanche Gulch. Wind slabs had formed on leeward aspects, and more southerly facing slopes were subject to  rapid warming during the day.  This warming combined with sun exposure produced a layer of heavy, wet snow on the surface with lighter, drier snow underneath.  With cold overnight temperatures this may have produced a bit of a crust layer on the snow's surface.  An extended column test was performed resulting in a score of ECTN27 Q2 at 20 cm deep with failure occurring at a density change.  There was not temperature gradient present.  Tree bombs were prevalent below treeline with some roller ball activity witnessed on open, sun exposed slopes. 

Observations were also made on Grey Butte by an MSAC forecaster.  There were no signs of any instabilities witnessed on all aspects.  A snow study pit was dug near the top of Grey Butte, just over 8,000 ft. on a NNW aspect with a 34 degree pitch (See graph and photo below) with obvious wind loading.  Multiple stability tests were performed to test bonding and stability of the newly wind deposited snow.  An extended column test was performed resulting in a score of ECTN25 Q3 at 42 cm deep at a change in density. A layer of graupel snow crystals exists at the interface of the new snow and the old snow surface that was "a little disconcerting", but tests were unable to produce any good, clean failure.  A propagation saw test (PST) was performed to test sensitivity of the graupel layer resulting in a score of 65/100.  ECT scores at both locations, Green Butte Ridge and Grey Butte, required a moderate to strong amount of effort to initiate a failure.  Both extended column tests did not show any propagation at the point of density change within the layer of new snow.  This leads to some uncertainty as to wind slab sensitivity to trigger.  Sensitivities will vary depending on aspect and elevation.  The stretch of warm and sunny weather over the coming days will help wind slabs to bond with underlying snow.  

For today, the biggest concern for areas where one may potentially find and trigger a wind slab avalanche will be above treeline, in the typical starting zones just below ridge tops, mid-slope depressions, the tops of chutes or couloirs, and around rock outcroppings, on leeward NW-N-NE-E-SE aspects, on slopes 37 degrees and steeper.  Day time warming may be limited today with increasing clouds, but loose wet snow instabilities may be present during the afternoon hours on southerly facing aspects.  Tomorrow, ample sunshine and increasing temperatures will make loose wet instabilities more prevalent.  The sunny skies and good visibility will draw folks to above treeline locations today where wind slabs exist.  As one gains elevation and the temperature cools, the old snow/new snow bonding may not be as good as near/below treeline areas.  Caution should be taken when choosing one's route of travel, and areas where wind slabs/pillows may have formed should be identified and avoided.  

Pit Profile from top of Grey Butte on 2-20-2016:

Photo of Grey Butte Pit Profile highlighting most recent snow layers:

View of Old Ski Bowl, South side of Mt. Shasta, from the top of Grey Butte:

Pit Profile from WNW aspect of Green Butte Ridge on 2-19-2016:

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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 lake. 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.