Avalanche Forecast

A weak disturbance will move across the region Saturday, causing moderate to strong NW ridge level winds may build new fresh wind slabs on lee slopes, near and especially above treeline. 

Light snow showers Saturday may bury intact a variety of weak surface snow types formed this week under fair cold weather.

Local wind slabs from the recent E-NE winds are likely Saturday. This should be mainly on westerly to southeasterly aspects near ridges.

Watch for firmer wind transported snow on all aspects, mainly near and especially above treeline.

The December 8th layer continues to round and gain strength and should be less sensitive to trigger.  Do head for lower angle slopes and ratchet back your plans if you experience collapsing or whumpfing or have evidence of this layer such as from snowpits.

Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.

Weather and Snowpack

The last storm cycle to affect NW, Washington Cascades was from late Thursday, December 8th through Monday morning, December 12th. About 3 inches of water equivalent and over 3 feet of snow were recorded at the NWAC station at Mt Baker ending Monday morning Dec. 12th. 

Fair and cold weather this week has been interspersed with periods of moderate N-NE-E winds both Wednesday and again Friday. These winds were strong enough to build fresh wind slabs on more atypical SW-NW facing terrain, mainly near and especially above tree line.

There has been about 12 inches of snowpack settlement since the storm cycle ended, allowing underlying or storm snow related weak layers to stabilize. 

Several clear nights with light winds this week have allowed for weak surface snow development. On wind and sun sheltered terrain, extensive near surface faceted snow or surface hoar have formed this week and this may be an important weak layer if buried intact by the expected return of light snowfall Saturday.

A thin sun crust is likely to have formed on steeper southerly facing slopes, which also may be a future interface for avalanches when loaded with sufficient wind transported or future storm snow.

Recent Observations

A regional avalanche cycle was seen December 8th-11th especially along the west slopes with some avalanches releasing on the December 8th persistent weak layer in the Washington Cascades. 

The Mt Baker pro-patrol reported decreasing avalanche control results on Monday with only local new 7 inch storm slab on sheltered slopes.

Skiers and riders have been accessing steep terrain over the past few days with no reported avalanche incidents in the Mt Baker area. 

NWAC observer was in the Yellow Aster Butte area near Twin Lakes Friday. Strong NE ridge level winds were transporting significant surface snow and building sensitive fresh wind slabs on atypical South - West facing terrain. These new wind slabs changed to intended objectives, opting for safer lower elevation terrain. Even so, where small areas of wind slab were encountered, they were sensitive to trigger. These new wind slabs are the primary concern in this zone.

In the same area, the December 8th persistent weak layer is becoming more difficult to find and gaining strength through gradual rounding. Snowpack tests on this layer Friday in that area were unreactive.

There are a variety of current snow surface types awaiting our next storm snow, including surface hoar, near surface faceted snow, sun crusts, wind sculpted snow, and low density snow in protected areas.