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RegisterDec 11th, 2015–Dec 12th, 2015
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Travel conservatively by staying off steeper slopes and avoiding wind loaded terrain near and above treeline, especially later in the day. The above treeline winds are forecast to be quite strong Saturday afternoon, so don't underestimate the rapid loading occurring at higher elevations. Persistent slabs now seem unlikely to trigger in the NE zone, but we will wait for more information before dropping this avalanche problem as they still have high consequences.
Light snow should begin by mid-day and slowly increase throughout the afternoon and early evening. Combined with increasing southerly transport winds in the afternoon, there will be an increasing avalanche risk late in the day for the near and above treeline zones.
New wind slab quickly building on lee NW through E slopes Saturday afternoon will be the primary storm related avalanche problem near and above treeline. In contrast, storm slabs are less likely by later in the day.
Persistent slabs now seem unlikely to trigger in the NE zone, but we will wait for more information before dropping this avalanche problem all together. Look for obvious clues to turn around like whumpfing or shooting cracks as evidence that persistent slab is an avalanche problem in the near and below treeline zones.
Use extra caution if traveling into the above treeline zone as there have not been any recent observations from this elevation band.
Snowfall over the east slopes the first week of December was about 1-4 feet. Then an atmospheric river arrived early in the week with additional snow in the northeast zone, rain in the southeast zone, with a transition in between in the central east zone. Almost 4 inches of water accumulated in 48 hours for Washington Pass and Holden ending early Thursday morning.
Avalanche and Snowpack Observations
We have varied conditions along the Cascade east slopes! The forecast discussion is the same for the east slopes, but the danger ratings and problems differ by zone.
A regionally deep snowpack exists in the northeast Cascades. Recent heavy precipitation along with a warming trend has likely thoroughly tested or buried persistent weak layers from earlier in the season. Avalanche problems are more likely to be storm related in the northeast zone. Persistent slabs now seem unlikely to trigger, but we will wait for more information before dropping this avalanche problem all together.
NWAC observer Tom Curtis was at Blewett Pass in the central east zone Wednesday and found sudden collapse test results in faceted snow at the November crust 15 cm from the ground. On Thursday, Tom found similar sudden collapses with buried surface hoar averaging 50 cm down at 5100 ft on the north side of Mt. Cashmere. More importantly Tom experienced whumpfing as this layer collasped and heard a natural avalanche release far from his observation location. We don't know how this layer fares as one moves further up in elevation, thus we'll forecast conservatively until more information is known about lingering PWLs in the central-east Cascades. Further east in this zone, Mission Ridge pro patrol had did not find the recent storm snow particularly reactive during control work Friday morning, nor was there any evidence of lingering weak layers.
The southeast zone should have a much shallower and more stable snowpack affected by recent rain and warm temperatures. We have not received any observations from this zone.