Avalanche Forecast

A frontal system overnight should enhance and cause increasing winds and precipitation rates, before changing to showers with cooling Friday.   

Avalanche problems Friday should be associated with new storm and wind slab layers. New and recent snow will be deposited on a wide variety of lee aspects, mainly from NW and E facing. Most avalanches should be confined to the new storm snow since Thursday, but a few may step down to older storm layers or crusts in isolated locations. Watch for areas where buried surface hoar may exist from Thursday morning, mainly just east of the Stevens Pass area.   

Near and above treeline, increasing snowfall and winds, is expected overnight Thursday and early Friday. This should cause sensitive storm layers. Therefore, best to avoid steeper slopes and those showing signs of recent wind loading.  

Terrain anchors are still causing significant anchoring at the lowest elevations. Use caution near creeks which are still open in some areas.

An atmospheric river around Dec 9th pushed heavy rain up to at least 6000 feet in the north Cascades and near or above 7000 feet in the central and south. Below these elevations liquid water percolated down below the early December crust (date when the crust was buried) and is expected to have eliminated or subdued any persistent weak layers of mainly buried surface hoar formed in late November. An active and cool weather pattern over the last week has produced about 2 to 3 plus feet of new snowfall that now sits over the 12/9 crust. Snow depths below treeline are increasing nicely, but many barely hidden hazards like rocks, streams or snags remain. The skiing in non-wind affected areas with enough snow cover has been good! 

Last weekend, most avalanches released within storm layers, but a few released down to the recent rain crust. Storm instabilities have had time to heal and no new avalanches were reported Tuesday or Wednesday. The NWAC staff along with other Stevens Pass professionals had field training Monday and Tuesday in the Stevens Pass area and found a reactive but strengthening graupel or low density stellar crystal layer about 35-40 cm below the surface. The snowpit tests failed to indicate propagation was likely. Moderate west-northwest winds in the above treeline zone along with light amounts of new snow received Tuesday night through Wednesday morning have likely redistributed recent and new snow onto lee easterly slopes in the near and above treeline zones. 

Newly formed and extensive surface hoar was evident Wednesday afternoon in the Stevens Pass area, near Rainy Pass. This layer may have been buried intact early Thursday with the onset of the current storm.  

Further observations by Tom Curtis in the Icicle Creek drainage Thursday, failed to identify the persistent layer of buried surface hoar found prior to the rain event December 8-9. There was significant evidence that the  rain event has destroyed this layer. Coupled with other recent observations along the east slope areas, we are removing the PWl from the mentioned avalanche problems. 

Recent guide reports from the Washington Pass zone indicate strong northerly winds redistributing recent snow on lee southerly aspects above treeline. The most recent storm snow was reported to be well bonded to the underlying crust, with good ski conditions found in non-wind affected terrain.  

The southeast zone should have a much shallower snowpack, more affected by recent rain and warm temperatures. However, we have no recent observations from the southeast zone.