Wind speed have tapered off overnight and are expected to be moderate in wind channeled terrain and calm- light in more protected areas.  This decrease in wind speed will bring an end to additional redistribution of surface snow.  This will allow the snowpack to settle and natural avalanches to become unlikely.  Human triggered avalanches will remain possible 6 inches- 2 feet in depth, although the sensitivity of wind slabs is decreasing.  Our main concern moving forward is that buried surface hoar from 2/23 is suspected to exist under older wind deposits from 2/25-2/27 .  This may allow wind slabs to remain reactive longer than what is typical (see problem 2).  Natural avalanche activity on south aspects has been reported at mid elevation as recently as 3/4 (see avalanche activity).  The weak layer mentioned above is not expected to be widespread, but without digging to identify the layer, assessment will be difficult. 

At this point wind slabs will likely be very stiff (pencil-knife hard).  This will decrease the sensitivity of wind slabs but once initiated would produce wider propagations (larger avalanches).  It is very possible that failure may occur behind a person or machine, once they have moved onto the slab.  

  Wind slabs will have a hollow drum like feel and may have a smooth pillowed appearance.  Watch for signs of instability such as shooting cracks, collapsing and recent avalanche activity, although these may not exist even though unstable conditions may be present.

There are currently multiple persistent weak layers in or mid – upper snowpack that we are tracking.  The layer that is currently most concerning is the 2/23 buried surface hoar layer.  The distribution of this layer is currently unclear, but it does appear to exist at mid elevations on southerly aspects in some locations, and is capped by wind slabs from 2/25-27 wind event and more recently the 3/2-4 wind event.  Several large natural avalanche have occurred over the last week  on southerly aspects around 4000′ that indicates this layer needs to be a consideration in our terrain choices. The most likely place to find this layer will be at mid elevations on southerly aspects where wind slabs exist or in areas sheltered from recent wind affect.  This layer is less likely to exist in north facing terrain that has been affected by wind, as recent winds have probably stripped it away.  

Signs of instability may not be present, especially in areas where dense wind affected snow exists at the surface.  Digging snow pits will be the best way to identify this layer.

Other persistent layers of concern include the 1/14 buried surface hoar which is likely the responsible failure plane of some very large recent avalanches triggered by cornice fall.  Human triggered avalanches at this layer are currently unlikely due to their depth (80-150 cms).  But if they were to occur, would likely be in areas where a thinner snowpack exists and this layer is still relatively close to the surface (less than 3 feet).  

The last layer we are tracking in the mid- upper snowpack is the 1/25 rain crust/ facet combo.  This layer exists below 2500′.  Collapsing in the Intermountain and Continental zone has been observed at low elevations failing at this layer.  Natural and human triggered avalanches have not been reported at this layer and stability tests continue to show a lack of significant results and rough shears.  Even though human triggered avalanches are unlikely at this layer, it is still worth investigating if choosing to travel in steep consequential terrain at low elevations.

As the sun came out on 2/20 for the first time in weeks cornice failure began to occur that triggered very large avalanches (D2-D3). Activity has slowed over the last few days, but may pick once again as another big change in weather occurs over the next few days.  A strong inversion is expected to take shape that may push temperatures above freezing from 4000-5500′.  This sudden increase in temperatures will be putting increasing stress on cornices that have been recently growing with strong outflow winds.  Avoid exposure to cornices as the change in weather is underway.

 Cornices have been observed and reported as being larger than normal and poorly attached.  Cracks on ridge tops showing cornices separating from ridge lines have been observed and reported.  Cornices have continued to grow in size with strong winds.

Cornices are an objective mountain hazard that should always be a concern.  Although, recent activity strongly shows that we need to keep an extra cautious approach to avoiding overhead exposure to cornices.  Avoid traveling below or on top of cornices.  The avalanches that cornice fall has recently produced are unsurvivable events.

Recent outflow winds have stripped many areas with has led to an overall decrease in the mass of our snowpack.  Some areas did see depositions add to the depth of the pack, but the strength of winds we received has done more scouring, stripping and sublimating than redistributing and depositing.  One effect of this, other than damaging riding conditions is that depth hoar is now closer to the surface.  Depth hoar has been dormant nearly the entire season and has not been a major concern except during major loading events.  The most likely place to affect this deep layer are in areas where the snowpack is thin and a person or machines weight can directly effect this weak snow.  The overall snowpack has become thinner over the last week in most locations.  This has in turn created a net increase in probability of affecting this weak snow.  Another affect of depth hoar being closer to the surface is that these grains that are currently rounded may be moving toward faceting as temperature gradients increase.   Currently affecting this layer remain unlikely.  Although, may become an issue later in the season especially if our snowpack continues to be eroded by strong wind events, and an extended period of clear and cold.

This weak snow mentioned above was created by early season cold temps, dry conditions and strong north winds.  Poor structure near the base of the snowpack has been observed since late November.  Mild temperatures and consistent snowfall during mid winter allowed this weak snow to slowly round and gain strength.  This weak snow has been dormant through the majority of the season with human triggered avalanches being unlikely at this layer.  As the sun has come out on 2/20 for the first time in weeks several very large natural avalanches  occurred with cornice and ice falls being the triggers.  Human triggers remain unlikely at this layer, although these events show that large triggers can affect this weak snow.  Cornice fall will be the most likely trigger to affect this weak snow, although it is possible that a large group could have the same affect.  Avoid overhead exposure to cornices.

In most location facets near the ground have been found to be rounding and unreactive in stability tests.  In thin areas of the snowpack basal facets have been found to be more developed.  If you find it is possible to push a ski pole to the ground in areas you travel, assume that a weak faceted snowpack exists in that location. These areas could act as a trigger point.