Register for an account and never miss a forecast again!
RegisterRegister for an account and never miss a forecast again!
RegisterDec 25th, 2017–Dec 26th, 2017
.
Wind slabs that have formed during the last week should continue to stabilize Tuesday. Avoid steeper terrain features with firmer wind transported snow and use extra caution when transitioning into potentially wind affected terrain. Also, a large degree of uncertainty still exists surrounding the mid-December weak layer, so dial back terrain selection to preserve a margin of safety.
Brief high pressure should rebuild along the PNW coastal areas Tuesday. This should maintain partly to mostly cloudy skies and light winds with little change to the cold airmass in place.
This weather should allow for continued gradual settlement of any recent storm layers or wind slabs in higher exposed terrain. However, cool temperatures will help slow this process and may preserve wind slabs in higher terrain. Watch for wind stiffened snow on a variety of aspects, including non-traditional aspects from recent northerly winds and easterly winds channeled across the Cascade barrier.
Lots of uncertainty exists around the distribution and sensitivity of the 12/15 layer. Limited observations on this layer make it difficult to forecast although it is most likely to persist in wind-sheltered locations. 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.
Also, despite all this new snow, early season hazards still exist at lower elevations and especially around creek beds that are not filled in.
Up to 3 inches of new snow fell on the east slopes in the 24 hours ending Sunday morning, which added to a few inches of accumulation 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 and possibly again Sunday redistributed snow in exposed and wind prone areas forming wind slabs on a variety of aspects.
A large amount of uncertainty remains 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.
A rain crust, a few inches above the 12/15 crust, is seen in some pits in some areas below treeline east of the crest.
Snow depth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger.
Observations
North
Many observations are coming via the NCMG for the Washington Pass corridor through the week.
On Saturday in the Washington Pass Hairpin area on southwest slopes 5500-7200 feet recent snow was well bonded and small steep slopes did not give results in slope tests. There was widespread new surface hoar.
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 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.
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