Avalanche Forecast

Increasing storm conditions Saturday. Light rain and snow should increase early Saturday through the day, becoming moderate with increasing westerly crest level winds. This should build unstable storm and wind slab layers through the day, with wind slabs spreading to NE-SE facing exposed terrain, especially below ridges by afternoon. 

Expect dangerous avalanche conditions near and above treeline, especially by late Saturday afternoon. Careful snowpack evaluations, cautious routefinding and conservative decision-making will be essential Saturday. 

Exercise extreme caution near avalanche terrain in this area due to the persistent slab identified in the snowpack discussion. Subsequent snowfalls may make this layer tougher to trigger... But the increasing slab depth, especially on wind loaded slopes translates to larger avalanches. Slides beginning in new storm layers may possibly step down to this more deeply buried layer, where present.  

Professional observers and mountain guides are treading carefully with this snowpack structure and gravitating toward lower angled (but still enjoyable) terrain not connected to large avalanche paths.   

The most recent snowfall occurred in the NE and Central WA Cascade east slopes Tuesday and Tuesday night when about 10 inches accumulated (Harts and Washington Passes).  This snowfall began relatively warm and cooled through the deposition, hopefully forming a desirable new snow profile. Moderate NW crest level winds accompanied snowfall and likely created wind slab conditions on the favorable SE lee facing terrain below ridges. No first hand observations have been received since that snowfall in the NE zone.

A warm and moist storm system preceded that, over last weekend with moderate snow with a change to rain at lower elevations before cooling. A natural avalanche cycle likely peaked late Saturday night through Sunday morning, (Dec. 20-21) during the height of the warming (Hart's Pass Snotel peaked at 31 deg F Sat night). 

Important observations arrived via our pro-observers, North Cascade Mountain Guides and the NWAC Recent Observations page describing a persistent weak layer 50-100 cm below the surface. The PWL consists of a facet/crust combination formed earlier in December. Remotely triggered avalanches were reported in the Washington Pass area Monday, as well as a large natural avalanche on an E aspect in the Cutthroat drainage that likely ran during the weekend cycle. The PWL was generally found on south-east aspects near and above treeline, but we cannot rule out other aspects at this time.  

Pro-observer Tom Curtis was in the Lake Wentachee area Wednesday. He found rounding facets closer to the surface in the shallower snowpack of Dirtyface Mtn near treeline on a southeast aspect. The fracture character of this layer showed sudden collapses in column tests. While the slabs are shallower in the East Slopes Central zone... they would be easier for a human to trigger.  

Remotely triggered slab avalanche near Washington Pass, Dec 22nd. Photo by CB Thomas.