On 4/9 E-NE winds built shallow wind slabs (4-12 inches) in specific locations,  these have been reactive to human triggers in isolated locations where they overlie faceted snow.  Wind slabs mentioned above 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.

Another round of light snowfall is expected today that will add to the depth of storm slabs.  New snow amounts since 4/11 have favored coastal areas.   On 4/13 a foot of uncohesive snow was found on shaded (northerly) aspects above 4000′ in the Intermountain/Maritime transition zone.  Human triggered storm slab avalanches 6-16 inches in depth are possible today where new snow has been stiffened into a slab by the sun or by wind.  In high elevation protected north facing terrain, human triggered dry loose avalanches are more likely than storm slabs due to very little cohesion in the surface snow.  The sun plays a major role in snow quality and stability this time of year.  Realize that even small changes in aspect can have a big affect on snow stability and quality.

Convex and wind loaded terrain will be the most sensitive to human triggers today.  Use test slopes and hand shear tests to determine how well new snow has bonded with the snowpack.  Pay attention to the cohesion (stiffness) of the new snow and realize that stiffer snow= slab, and these have the possibility of being triggered by a person or machine in steep 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).

Elevated freezing levels today will increase the likelihood of wet loose activity at low elevations on east, south and west.  The amount of activity we receive today will depend on the amount of cloud cover that remains throughout the day.  If the sun comes out wet loose activity will be likely on east and west aspects at low elevation, and south at all elevations up to 6000′.  Steep rocky terrain will be the first areas to be affected.  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.