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RegisterDec 23rd, 2017–Dec 24th, 2017
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Avoid steeper terrain features with firmer wind transported snow. Be prepared to step back from your plans if the next system arrives stronger and sooner than expected. The extent of a persistent slab is still uncertain, use conservative terrain selection to maintain a margin of safety.
The next system should begin to bring light snow mainly the south Cascades Sunday afternoon. Alpine winds should stay fairly light with no great change in snow levels or cool temperatures.
Keep an eye out for previous or newly forming wind slabs on Sunday. Winds will have potentially loaded non-traditional aspects. If you see signs of winds transporting snow including plumes, drifts, and uneven snow surfaces, then avoid slopes where the wind loading is occurring.
Be prepared to step back from your plans if the next system arrives stronger and sooner than expected.
Also despite all this new snow, early season hazards still exist at lower elevations and especially around creek beds that are not filled in.
Lots of uncertainty exists around the distribution and sensitivity of the 12/15 layer. Limited observations on this layer make it difficult to forecast. When uncertainty goes up, terrain selection must go down to maintain wide margins of safety. Time and patience will allow this layer to gain strength.
A few inches of light snow fell across the east slopes of the Washington Cascades in the 24 hours ending Saturday morning. Up to about 3 feet of recent snow sits atop the 12/15 crust/persistent weak layer. Overall recent snow has been gaining strength leading to a recent stabilizing trend.
Ridge top winds Tuesday to Thursday redistributed snow in exposed and wind prone areas forming wind slabs on a variety of aspects. Limited information about the location and sensitivity of these winds slabs has been received.
A large amount of uncertainty exists around the 12/15 crust/persistent weak layer. This layer has generally been observed at elevations below 6000 feet. Snowpack tests in a few locations continue to demonstrate results and the potential for an avalanche to propagate. The limited amount of incoming information makes it difficult to paint a clear picture of this potential avalanche problem.
Another rain crust, a few inches above the 12/15 crust, is seen in some pits in some areas below treeline east of the crest.
Snowdepth decreases substantially the further east from the Cascade crest. In many areas below treeline, there is not enough snow to present an avalanche danger.
Observations
North
Many observations are coming from the NCMG through the week.
On Thursday on Delancey Ridge they noted blowing snow, moderate CT results in storm snow and a ECTP result between crust layers at about 48 cm.
On Friday at the Washington Pass Hairpin they found 45-65 cm of storm snow on the 12/15 crust, with an ECTP21 result in 2 cm buried surface hoar on the 12/15 crust. However, the buried surface hoar was not seen in pits above 5300 feet.
On Saturday in the Washington Pass area recent snow was well bonded and small steep slopes did not give results in slope tests. There was widespread new surface hoar.
Central
On Thursday, professionals on Dirtyface Peak observed the 12/15 layer/PWL interface reactive in PST and ECT tests at 5000 ft on an east aspect. The interface was 2.5 ft down. Wind transport was occurring near and above treeline and actively loading lee slopes. Recent storm instabilities were healing.
South
No recent observations