Avalanche Forecast

You will be able to trigger a variety of different avalanche problems Thursday. This complicated scenario deserves respect. Stay off all steep open slopes where avalanches may start.

New and reactive storm slabs and wind slabs will have formed Wednesday night. These will be larger and easier to trigger in areas receiving more snowfall and wind, particularly around Mt Baker and Mt Rainier. Identify and avoid slopes where winds have deposited new snow. In some location soft non-wind-effected snow may cover new wind slabs making them harder to identify. Stay off of any slope you expect may have received wind loading from the predominantly southerly winds during the storm. These areas may exist far below ridge-line and on mid-slope cross-loaded features.

In sheltered areas, you will be able to trigger soft storm slabs on slopes greater than 35 degrees. Subtle changes in temperature and snowfall rates formed weak layers in the new snow. These layers need time to heal.

Weak old snow layers found on slopes that have received direct sun were buried on 2/23. This persistent weak layer resulted in several avalanches 1.5-3 feet deep. Snow profiles and snowpack tests can show the presence of this layer but cannot prove its absence.  This layer will still be able to be triggered by backcountry travelers on Thursday. 

While it is not listed as a problem, there is still a potential for a Deep Persistent Slab avalanche to occur. These avalanches are becoming increasingly difficult to trigger, but may be caused by a smaller avalanche stepping down to older deeper weak layers or a cornice fall. The best way to avoid this low likelihood-high consequence problem is by avoiding triggering smaller avalanches in the surface snow.

New snow fell around the western regions of the Cascades beginning Wednesday. New snow combined with moderate to strong winds to transport snow in exposed terrain forming new wind slabs.

On E-S-W aspects, a thin breakable sun crust was formed early last week and buried on 2/23. Very small weak facets have been reported surrounding the crust. This was the weak layer found or suspected in several avalanches 1.5-3 feet deep. This layer has not yet had significant time to heal. It is found 2-3 feet below the surface on steeper slopes that have received direct sun during the past week.

Some observations suggest the presence of other persistent grains at this same interface on shaded slopes. Buried surface hoar and large preserved stellars have been reported in recent avalanches and snowpack tests at this interface.

Avalanche and snowpack observations continue to indicate that avalanches are possible on a layer of weak sugary facets buried on 2/13. This weak layer is generally 3 to 5 feet below the snow surface just above a very firm melt-freeze crust (2/8).

There are no significant layers of concern below the 2/8 crust.

Observations

On Wednesday NWAC professional observer Lee Lazzara traveled in the Mt Baker backcountry. Lee reported wind slabs forming on a variety of aspects near treeline. Snowpack observations showed a highly variable snowpack, but the facet/crust combination was found on steep sunny aspects 2 feet below the snow surface.

NWAC professional observers in the Crystal area Tuesday and Wednesday observed the 2/23 interface, involved in two previous avalanches, still reactive in snowpack tests. In this area the 2/23 layer was found 1-2 feet below the snow surface.

Avalanche and snowpack observations from around the western regions of the Cascades and Passes continue to indicate that propagation of an avalanche on the 2/13 facets is possible. This layer has been found 2.5 to 4 feet below the snow surface.