Avalanche Forecast

Cloudy skies and inversion conditions with continued cold temperatures 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.

We have removed Persistant Slab as a problem on the East slopes of the Cascades because observations over the past 5 days don't show evidence that it is a problem. It cannot be ruled out that pockets of persistent slab could be triggered somewhere in the range.

Also, despite all this new snow, early season hazards still exist at lower elevations and especially around creek beds that are not filled in.

Freezing fog has been observed in some low to mid-elevation locations, creating a crust east of Snoqualmie Pass, deposited by a layer of low cloud capping an inversion east of the crest.

Since last Wednesday, areas east of the Cascade Crest have seen several small refreshers each delivering 1-3" of low density new snow to the east slopes over the past 5 days. 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.

Some comments below from a Professional Guide in the Cascade East - North zone help reduce some of the uncertainty surrounding the crust/persistent weak layer distribution. 

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

A summary of professional guides reports regarding the persistent weak layer problem for the East-North Zone:

• In the above treeline zone, small faceted grains exist and are rounding and gaining strength, down 70 cm and below the storm snow that accumulated starting 12/15. They have not been reactive on tests.
• Solar aspects near treeline are bonding well to a strong solar crust buried 12/15. However, the cannot rule out surface hoar in some sheltered larch glades around 6000 feet.
• Below treeline, the guide observed the surface hoar buried 12/15 down 70 cm in flat meadows and creek valleys, but has yet to find it in avalanche terrain. 
• Aggressive terrain has been skied and has not shown signs of being reactive in recent days.

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