Avalanche Advisory for 2014-12-20 07:07:43

Over the course of this past week, we have seen upwards of two feet of new snow. A slow trickle of precip has added snow slowly to our snowpack over the week and allowed for favorable stability for sliders and riders below and near treeline areas. Visibility has been poor and yesterday the 'soup de jour' was split pea. At 7,900 feet, 1145 hours, the temperature was 32 degrees with a light mist and intermittent snow/ice pellets. Brief glimpses of blue sky occured but never lasted.  The snow conditions in general below and near treeline were DEEP and pretty heavy. Snow density measurements recorded 20% water content within the top layers of the snowpack. All said, our December base is looking great!

The surface hoar layer that formed earlier in the week and was subsequently covered by new snow was difficult to find yesterday in pit profiles. Warm temperatures have eliminated this weak layer and it doesn't seem to be a probelm any longer. Bless our maritime snowpack for this.

Total snow depth observed at 7,900 feet at the top of T-Bar was 240cm. A 157cm deep snow pit revealed an isothermal snow mass with no temperature gradients. Stability test scores (extended column tests) were all in the 20-30 range with poor shear (ECTN26@105cm/ECTN21@105cm). This "weak" layer consisted of a density change in the snowpack.  

The big picture: Below and near treeline snow stability seems very good. Lack of observations for above treeline areas leaves some uncertainty for these areas once the clouds begin to part. We have a number of variables that are not particularly favorable for a stable snowpack above treeline. These are: recent new snow and no recent upper mountain observations, rising temperatures/snow level (upside down cake effect), additional snow in the forecast (5-9 inches >10,000 feet) today and finally strong west/northwest winds on tap (mid to upper mountain levles - 50-60 mph). Once again as we saw last weekend, once the visibility improves and folks venture above treeline, extra caution should be exercised!

Small to large, wind and storm slab avalanches will be the avalanche problems for this weekend and could be found on all aspects, mid to upper mountain levels. Stay clear of lower angle run out zones, leeward aspects near ridgetops, bowls, extreme terrain, couloirs, convex rollovers, and near rocks.

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 still has very little snow.

Mt Eddy area is hosting about 34 inches of snow in Wagon Bowl. I have not been up into that area yet and have received no reports.

Sand Flat Winter Trails: OPEN

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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.