Avalanche Forecast

Avalanche conditions will not significantly improve Monday. You will still be able to trigger Persistent Slab avalanches that are big enough to kill you on slopes steeper than 35 degrees. Persistent Slabs can surprise even very experienced travelers and can break over terrain features. Put a wide buffer of terrain between where you travel and any steep slopes. Use extra caution in areas where avalanches could come down from above. Avalanches may be surprisingly large and run farther than you expect. Make conservative terrain choices until we know more about these avalanches.

Cold temperatures will slow recent wind slabs from stabilizing. N-NE winds near and above treeline will transport recent snowfall onto lee slopes Monday, forming fresh wind slabs. Due to shifting winds, 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. Triggering a Wind Slab could dig into deeper layers and result in a large Persistent Slab.

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 the usual playbook of waiting a day or two for storm instabilities to settle out does not apply.

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 for Monday.  

About 14 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. We have many reports of similar Persistent Slab structure in the Cascades with surprising and widely propagating avalanches observed in the Snoqualmie Pass area over the weekend.

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

Upslope 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. 

On Friday, National Park Rangers triggered a large avalanche that crossed from a northeast to east aspect near treeline. The avalanche was 70 feet wide and cracks propagated beyond the crown. On Thursday, NWAC observer Matt Schonwald and NPS Rangers were on Mt Angeles. They observed 4 inches of weak sugar-like snow on the surface (near surface facets) on all aspects and elevations traveled. They were able to trigger a small isolated wind slab on an E aspect near treeline.