Avalanche Forecast

Little change in the overall weather pattern is expected Wednesday. Continued cold temperatures with relatively light winds Wednesday will not significantly improve the current avalanche danger in this zone. A slab avalanche was triggered that was big enough to kill a person on Monday and the same conditions should persist Wednesday, especially on non-solar facing steep slopes greater than 35 degrees. 

Persistent Slabs can surprise even very experienced travelers and can break over terrain features and run long distances. Avoid large terrain, especially areas exposed to avalanches that could come from above. Avalanches may be surprisingly large and run farther than you expect. Make conservative terrain choices until we know more about these avalanches. A small triggered Loose-Dry avalanche or a small Wind Slab may be enough to trigger a Persistent Slab.

Cold temperatures will allow recent slabs to persist longer than usual. Avoid steep wind loaded terrain especially near and above treeline on all aspects. Wind sculpted features, cracks in the snow, pillows, cornices, and variable height of recent snow are all indicators that you could trigger a new or old Wind Slab avalanche. A Persistent Slab could be more easily triggered in an area where the slab is thinner, such as near rocks or trees. 

The combination of Wind Slab and Persistent Slab requires very cautious decision-making and terrain selection. Persistent Slab avalanches are not common in the Olympics and require additional safety margins.

Small loose dry avalanches are likely on very steep slopes and could be problematic around terrain traps. They will not be listed due to larger and more dangerous avalanche problems forecast Wednesday.  

Cold temperatures and refreshing snow showers over the past few days have added light amounts of low density snow to the snowpack with light winds. 

About 18 inches of new snow has fallen on weak old surfaces in the Hurricane Ridge area since 2/15. Near surface facets and surface hoar were observed on all aspects near treeline prior to the weekend storm cycle. These weak sugary facets were formed over a hard crust, creating both a smooth sliding surface and a very weak layer above. Where a slab exists above, that is maintaining the possibility of deeper slab releases. The cold temperatures are helping preserve the weakness at this interface.

There have been many reports of similar Persistent Slab structures throughout the WA Cascades, with a few widely propagating avalanches observed in the Snoqualmie Pass and Stevens Pass areas Sunday and Monday.   

In exposed terrain at Hurricane Ridge, winds have formed drifts on lee slopes. N-NE winds Sunday likely redistributed snow onto unusual aspects. Below the weak facets in the upper snowpack there are no other layers of concern. Warm wet weather from the first week of February has created a relatively uniform and consolidated lower snowpack.

Observations

Monday 2/19, snowboarder triggered slab, East aspect of Maggies, est. 2 ft crown, no injuries. Suspected release on 2/13 facet-crust.

No observations since Monday.

NPS Rangers on Monday saw crown from recent Slab Avalanche release on Mt Angeles, SE aspect, size difficult to determine.

Additional relevant obs from Monday. 

Up slope snow showers added a few inches of low density snowfall to the Hurricane Ridge area Sunday, but heavier snowfall at lower elevations closed the Hurricane Ridge road so new new observations were received.