Human triggered storm snow avalanches are possible 1-2 feet in depth.  Our area is expecting 2-4 inches of snow today.  If we receive more than 8 inches of snowfall during the day the hazard will move to Considerable.

Several small storms have traversed our area over the last 72 hours depositing up to 2 feet of new snow near the coast with less than a foot on Thompson Pass and north.  Several interfaces between these storms exist that are sensitive due to continued snowfall despite the one day of blue skies on the 15th.  The good news is that in the majority of locations the surface snow is very uncohesive (no slab) and stable conditions have been observed and reported.  The concerning thing is the amount of loose snow that exists and conditions can turn from stable to reactive in close proximity.  This will largely be dictated by wind affect at the surface.  Where surface snow is stiffened by wind, a slab will exist and the likelihood of triggering an avalanche will increase.  These conditions have not been observed lately in the Maritime climate zone where new snow is the deepest.

In the Intermountain and Continental zone less new snow exists at the surface although wind affected surfaces have been observed in specific locations such as near high elevation ridge lines and wind channeled terrain.  Thompson Pass and north may have a slightly higher distribution of areas where triggering an avalanche is possible, but the depth is shallower.  Maritime instabilities will be deeper in areas where wind stiffened snow exists at the surface.

The main point is: Stability above 2500′ will directly correlate with the presence and depth of wind slabs at the surface.  

Human triggered avalanches are possible up to 3 feet in depth below 2500′ in the Maritime climate zone.  A rain crust formed on 1/25 has formed a potentially dangerous persistent weak layer in the Maritime climate zone below 2500′, this includes Keystone Canyon.  This layer has been identified on Thompson Pass and north.  Although has been found to be much less of a concern in those areas, but can’t be ruled out in steep and/or unsupported terrain.

On 2/16 this rain crust was found to have signs of instability at 1800′ just east of Benzene Alley.  These include one very large collapse and propagation present in both ECT‘s and PST‘s repeated multiple times 3 feet down (see observation page).  ECT propagation results were hard, indicating this layer will be difficult to trigger in most locations but the consequences would be high due to the depth of the slab.  This weak layer was previously found to be faceting creating an area of poor structure, although only recently has propagation popped up in stability tests.  This may indicate that the amount of snow we have received near the coast may be pushing this weak layer towards the tipping point.  Careful assesment of this layer is advised especially if traveling in steep and/or unsupported terrain below 2500′ in the maritime climate zone. 

Watch for signs of instability such as shooting cracks and collapsing.  Digging snowpits to assess stability in the area you choose to travel is a good idea if choosing to travel in steep terrain at low elevations in the Maritime climate zone.

Weak snow continues to exist near the base of our snowpack in all three climate zones.    The last recorded avalanche activity at this layer occurred during the 1/23-25 storm on Nicks Buttress / ~3500’/ north aspect (see avalanche activity section).    This layer is believed to be dormant as there has not been deep avalanche activity for 3 weeks, and only 2 observed in 2 months.   Human triggered avalanches are currently unlikely to occur that fail on weak snow near the base of our snowpack.

Faceted snow near the ground has been found to vary significantly from place to place.  In most locations this snow has been found to be rounding (gaining strength) and unreactive in stability tests.  In thin areas of the snowpack these facets are significantly more developed.  Unlikely does not mean impossible,  if a person were to affect weak snow near the ground it would be in areas where the snowpack is thin.

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, that could act as a trigger point.  An example of the difference in faceted snow that has been recently found can be seen below.

Depth hoar from Nicks Buttress ~4000′ North aspect 1/31. This was from an area where the snowpack 3 feet deep.

Rounding depth hoar on Cracked Ice / north aspect/ 3000′  on 2/11.  This was from an area where the snowpack was 7 feet deep