Strong north winds continue to affect our forecast zone with gusts to 75 mph expected early this morning on Thompson Pass. This has created wind slabs on lee aspects 6 inches-2 feet in depth (SE-NW) that are expected to remain reactive today on the lee side of terrain features, high elevation ridge lines and cross loaded gullies.  Buried surface hoar from 2/23 is suspected to exist under older wind deposits from 2/25-2/27 that may allow wind slabs to remain sensitive longer than what is typical (see problem 2).  Natural avalanche activity on south aspects has been reported at mid elevation as recently as 3/3 (see avalanche activity).

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.  

In a normal situation as wind slabs become as stiff as they are, the hazard would be decreasing.  Although, with the potential presence of buried surface hoar near the surface, the hazard remains elevated.   The weak layer mentioned above is not expected to be widespread, but without digging to identify the layer, assessment will be difficult.

Wind slabs will have a hollow drum like feel and may have 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.

An abnormal amount of Cornice falls have been reported last week that triggered very large avalanches (D2-D3).  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 will continue 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.

Weak snow created by early season cold temps, dry conditions and strong north winds have showed poor structure near the base of the snowpack.  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 last week several very large natural avalanches have 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.