Avalanche Advisory for 2015-02-28 07:01:22

Snow did fall on Mount Shasta yesterday from passing showers with periods of sun poking through.  Not a lot of snow was squeezed from yesterday's storm, which is typical for cold systems that come from the north, it was enough to act like a zamboni and smoothed out the snow surface.  Moderate northwest winds steadily blew through most of the day transporting snow by scouring wind exposed terrain, and depositing it in any dimple, gully bottom, low point etc.  For the most part, ski conditions yesterday from just above tree line (8,500 feet) to Bunny Flat was "dust on crust" with the occasional soft turn in patches that had collected up to 4-5 inches of wind deposited snow. It made for an enjoyable ski descent, however, it also presents our avalanche problem for the day which we'll get to in a minute. 

For the past couple of weeks, we have experienced day after day of sunshine and mostly mild temperatures working their melt/freeze magic. This has made for a bomber snow pack in terms of stability. That means it's very strong, isothermal, equitemperature, with no persistent weak layers of any concern.  This has also resulted in an overall smooth and firm snow surface that the new snow from yesterday is resting on.  The moderate north-northwest winds have deposited the new snow into shallow pockets on SW-S-SE-E-NE aspects .  The cooler temperatures during this storm made for lighter density snow, however, occasional sun breaks in between snow showers warmed up the new snow enough to create a change in density (ie. settlement) within wind deposited patches on leeward slopes.

Concern for today and the remainder of the weekend will lie within the wind slab avalanche problem.  The Old Ski Bowl weather station recorded close to another 2 inches of new snow in the last 24 hours. Grey Butte station has shown northwest winds blowing steadily during the storm, 20-30 mph with gusts to 64 mph, then dropping to 5-10 mph and variable in direction. These northwest winds have transported the new snow onto leeward aspects and formed small to medium slabs of varying thickness, 1-6 inches deep.  This spatial variability of scoured snow and wind slab patches will shape one's snow concerns for today. Smooth, round slabs have formed on top of the old snow surface and could be triggered by a skier or rider. That said, numerous hand shear tests and ski cuts within shallow wind slabs resulted in good bonding between new and old snow layers. Weak layers were above the old snow at density changes within the new snow. Leeward areas above tree line, near ridgelines and extreme terrain will be the best areas to find this avalanche problem (think S-SE aspects of Casaval Ridge above tree line and other similar slopes).  - Jon Dove

Photos:

Left: 4-5" thick wind slab on SE aspect of Casaval Ridge, 8,400 feet (J Dove)

Right: A ski traverse across SE aspect of Casaval, occasional, very small slabs 1-3 inches deep were triggered on lower angle slopes (J Dove)

Castle Lake and Mt Eddy zones are still hosting shallow snowpacks. All areas below about 6,000 feet in the forecast area are hosting patchy snow with dirt showing around trees and in sunny spots.

Report your observations to the MSAC! A photo, a few words... send them in! (nimeyers@fs.fed.us or 530-926-9614)

Castle Lake area has a shallow snowpack. Skiing is out of the question at this point due to lack of snow. 

Sand Flat Winter Trails: OPEN, trail conditions are firm and getting thin with some tree debris on snow surface. 

Pilgrim Creek Snowmobile Park: OPEN, however due to lack of low elevation snow, one must drive up the road several miles before enough snow is encountered. One CANNOT DRIVE over Military Pass. Snowmobiling is not recommended due to low snow depths.

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Terrain:  Remember most of the terrain that we like to play on is greater than 30 degrees.  Avalanches are possible on anything steeper than 30 degrees.  Avoid cornices, rock bands, terrain traps and runout zones of avalanche paths.

Weather:  Most of our areas avalanche danger will occur 24-48 hours after a storm. We still can see persistent weak layers from time to time and we always will be sure to let you know about that!  Heed the basic signs: Wind (significant snow transport and depositions), Temperature (rain/snow/rain/snow, which in turn weakens the snowpack), and Precipitation (Snow or rain add weight and stress to the current snowpack).

Snowpack:  If snow accumulates, give the snowpack a chance to adjust to the new snow load before you play on or near steep slopes (greater than 30 degrees).  Most direct action avalanches occur within 24-48 hours of recent snowfall.  Watch for obvious signs of snowpack instability such as recent natural avalanche activity, collapsing of the snowpack (often associated with a “whumphing” sound), and shooting cracks. If you see these signs of instability, limit your recreation to lower angle slopes.

Human Factor: Don’t forget to carry and know how to use avalanche rescue gear. You should NOT be skiing or climbing potential avalanche slopes without having beacons, shovels, and probes.  Only one person in a group should be exposed to potential avalanche danger at a time.  Remember, climbing, skiing, and riding down the edge of slopes is safer than being in the center.  Just because another person is on a slope doesn’t mean that it is safe.  Be an individual!  Make your own decisions.  Heed the signs of instability: rapid warming, “whumphing” noises, shooting cracks, snowing an inch an hour or more, rain, roller balls, wind loading, recent avalanche activity.

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