Avalanche Advisory for 2015-03-01 07:04:27

A chilly and windy day above treeline on Saturday, the last day of February. Yesterday, the snow surface conditions on Mt Shasta consisted of a mix of our exposed old, firm, wind-scoured snow with patches of fresh storm snow that has blown around and collected in gullies, depressions, and on leeward south and southeast slopes. We've had a storm total of 1-6 inches (depending on elevation) that has been accompanied by moderate to high winds, blowing from many directions, though primarily northwest and then easterly. The presence of wind was evident as any slopes exposed to wind were scoured of the lighter density snow that fell with the cooler temps. Up high on the mountain, blowing spin drift was visible for most of the day and it's certain that we've got some wind loading going on up there also. Below and near treeline, winds were light and new snow totals less, and thus conditions consisted of "dust on crust".

Winds have been a theme for most of the weekend. The most notable "event" was during the first wave of the storm. Northwest winds blew for a good two days, averaging 20-30 mph and gusting into the 60 mph range. Since the end of that event on the 28th, winds have let up at times with a few hours here and there of gusty, variable in direction wind, 15-30 mph with gusts into the 40's. Thus, we've seen most of the wind loading on south and southeast aspects, but other aspects certainly should not be left out.

Observations were made in several areas yesterday by Jon and I and also a local professional observer. Moderate concern has been focused on above treeline, southerly and easterly slopes becoming wind loaded and forming wind slabs near ridgelines, extreme terrain, bowls, gullies and depressions. Wind slabs were observed 6-12 inches deep on southeast slopes 8,500 to 9,500 feet. Numerous extended column tests conducted in the Old Ski Bowl and Sun Bowl areas produced ECTN 12-14 at 20-25cm down from the surface of the snowpack. Shear quality was very poor and this failure layer consisted of a density change in the snowpack. Further, old snow / new snow bonding was very good and we could not produce failure at this interface. We then got a report from a professional observer over in the Giddy Giddy Gulch area, similar elevation and same aspect, who heard a "whoomf" sound that caused some concern and uncertainty for us. This location where the "whoomf" was heard is the same location we've seen wind slabs form and triggered in the past. So, while Jon and I both thought that yes, we were getting moderate failures within the density change in the new snow, full slope propagation didn't seem likely due to poor propagation during ECT tests and also poor shear quality. That said, the full slope "whoomf" that was observed/heard would indicate that indeed some spatial instability does exists within newly formed wind slabs and backcountry travelers should use some caution above treeline today. Cooler temps could keep weak layers intact for the next few days and areas that are hosting just the right combo of conditions could see full slab failure.

The key will be to look for and stay off of steep slopes that host rounded wind pillows / slabs and realize that while small to medium in size, they could still be sensitive to trigger and be enough to sweep you off your feet and bury you. Once again, above treeline south and southeast slopes will be the best places to find said avalanche problem and will be most sensitive to trigger on slopes 35 degrees and steeper.

Photos below:

Left - Wind slab on a southeast aspect on 2.28.15 (N.Meyers)

Right - Generally scoured conditions for many areas exposed to wind. Ridgeline in background wind loaded, east/southeast facing. (N.Meyers)

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.