Avalanche Forecast

Previously moderate east winds should have diminished by Wednesday under mostly clear skies and gradually warming temperatures. When traveling into the near and above treeline zones, be prepared for recent wind slab formation on more southerly and westerly aspects. Older wind slab on more westerly aspects may still be sensitive in certain areas. Treat wind loaded slopes with caution, it is difficult to determine how sensitive they are with snowpack tests.  

 

A storm system moved through the Northwest on Saturday and Saturday night delivering some much needed snowfall. West winds changed to northwest, with moderate to heavy snow west of the crest and a cooling trend. A convergence zone contributed to snowfall in the central Cascades on Sunday. NWAC sites west of the crest picked up about 12-20 inches of storm snow over the weekend except lower amounts at Snoqualmie Pass due to initially very wet snowfall. 

Professional observers west of the crest reported storm snow instabilities quickly settling out and not exceptionally reactive over the weekend. The snow layering ended right side up with low density snowfall at the end of the storm.

NWAC observer Jeff Hambelton, touring on Mt Herman Tuesday, indicated the recent storm snow was well bonded to a rough old rain crust down some 30-40 cm. There was little evidence of wind slab with mainly lower density,unconsolidated surface snow providing excellent conditions with no avalanche activity noted. Some warming and sun affects were noted on direct southerly aspects where a thin sun crust had formed. 

East winds both through the Cascade passes and along ridgetop began to increase Monday then ease on Tuesday. This redistributed the recent snow on more S-W aspects. While the most recent storm snow avalanche problem should be decreasing, the recent wind slab will be an issue with certain aspects, generally near and above treeline. These wind slabs were noted by a recent observation submitted to NWAC Monday, indicting two remotely triggered hard slabs were released on the south side of Mt Baker.   

One notable exception for the west side zones is the presence of a spatially variable persistent weak layer in the Stevens Pass area. 2 out of 3 pro-observers have found PWLs over the last few days in this zone. Tom Curtis found a weak faceted layer 2-3mm thick in the mid-pack just east of Stevens Pass in the Nason Ridge area Saturday that propagated in snowpack tests. (See photo). Jeff Ward found a facet/crust combo at the bottom of the snowpack reactive in extended column tests on Cowboy Ridge near treeline almost 1 meter down on a SW aspect. 

With the amount of ski traffic in this area over the weekend and new snowfall making these layers harder to affect, we do not believe this problem is very sensitive to human triggering. However, the persistent slab problem will be added to the Stevens Pass zone with a low likelihood of triggering. 

Photo by T. Curtis 12-27-14 in the Stevens Pass area.  Location Nason Ridge/Rainy Pass 4900 ft