Avalanche Forecast

You can trigger dangerous Persistent Slab avalanches that are big enough to kill you. 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 slopes 35 degrees and steeper. Use extra caution in areas where avalanches could come down from above.  Avoid areas where the wind has recently drifted thick slabs over older weak layers. Wind sculpted features, cracks in the snow, pillows, cornices, and variable height of recent snow are all indicators of wind loading. Persistent Slab Avalanches are not common in the Cascades. Avalanches may be surprisingly large and run farther than you expect. Make conservative terrain choices until we know more about these avalanches.

About 1 foot of new snow has fallen on weak old surfaces in the Hurricane Ridge area. Near surface facets and surface hoar were observed on all aspects near treeline prior to this storm. We have many reports of similar Persistent Slab structure in other parts of the Cascades. Surprising and widely propagating avalanches have been reported from Snoqualmie Pass. In exposed terrain, winds have formed drifts on lee slopes. 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

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 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.