Persistent wind slab avalanches 4-12 inches in depth have been observed and reported in isolated locations on Thompson Pass and north.  Incremental snowfall along with E-SE winds that have alternated with NE winds have built shallow wind slabs on 4/9 in specific locations.  These are overlying a variety of surfaces including old hard wind affected snow and near surface facets (weak snow) from April 5th.  The difference in this interface will play a role in the sensitivity of persistent wind slabs.  

In isolated locations old wind slabs have been reported and observed as remaining sensitive where they overlie the 4/5 near surface facets.  This set up has been found in mid and upper elevation north facing terrain that was previously protected from outflow winds that occurred at the beginning of the month.  In the majority of areas along the road corridor, old wind slabs overlie very hard wind affected snow, in these areas the aforementioned slab has been found to be stubborn to unreactive to human triggers.  

Pay attention to the depth and sensitivity of old wind slabs and realize that this layer could be reactive in close proximity to slopes that are stable.  Careful snowpack analysis is required with this avalanche problem.

New snow amounts since 4/11 have favored coastal areas with up to a foot of new snow expected above 1500′ in the Port of Valdez.  This new snow has arrived with mild temperatures (mid 20’s- low 30’s)  and snowfall rates have been mild as well.  Both of these factors will promote bonding of the new snow with our snowpack.  With all that said, it is still currently snowing at sea level as of 6 am and human triggered avalanches will be possible  up to one foot in depth in steep terrain.  Convex and wind loaded terrain will be the most sensitive.  Use test slopes and hand shear tests to determine how well new snow has bonded with the snowpack.  This avalanche problems sensitivity will directly correlate with new snow amounts (higher snowfall= higher hazard).  Pay attention to new snowfall amounts, sensitivity, and wind distribution and allow these factors to aid in your choice of terrain.

On Thompson Pass and north, lower snowfall amounts have been observed with a trace at valley levels and 4-8 inches at upper elevations.  In these areas lingering wind slabs are the main concern (see problem 1).

The likelihood of wet loose activity will depend on the amount of cloud cover that occurs today.  New snow will easily be affected by the strong April sun.  Steep south aspects will be the first to show activity especially in steep rocky terrain.  So far this season wet loose activity has been below average.  Generally by this time of year steep solar aspects are beginning to lose mass by way of natural wet loose avalanche activity.  Many of these areas are still gaining mass, creating the potential for more substantial activity once temperatures rise to seasonal norms and wet loose/ wet slab activity begins in earnest.  Temperatures look to slowly stair step up this week but a drastic change is not yet in the forecast.

Timing is key in avoidance of this avalanche problem.  Pay attention to the amount of warmth that is being transferred into the snow surface (Is it becoming moist-wet?).  Avoid traveling on, or being exposed to, steep solar aspects as snow surfaces are becoming moist-wet.

Weak snow exists at the base of our snowpack.  This weak snow is currently unlikely to be affected due to the strength of old wind affected snow at the 3/17 new/old interface.  Depth hoar may become a concern later in the season if our area returns to a period of major snowfall and the very strong wind damaged layer at the new/old interface starts to break down and lose strength within the snowpack.  As very hard wind slabs break down within the snowpack, a person or machines weight will have a more direct affect on weak layers at the bottom of the snowpack.  In addition,  the increasing intensity of the sun will be putting pressure on deep layers during the heat of the day.

This problem is difficult to assess.  if we do see deep slab avalanches begin to occur in our forecast zone, they will likely first show up on south aspects.  This has not occurred yet, but would be a clear indicator of an increasing potential to see this avalanche problem on other aspects.