Avalanche Forecast

Another Pacific frontal system, in the long series of recent storms, is moving into the Cascades Tuesday evening. This next system will cause renewed light to moderate snow and light to moderate westerly winds Tuesday night. This should begin to build new areas of wind slab on lee slopes below ridges and create some isolated storm slabs. Moderate to heavy showers should persist with increasing westerly ridgetop winds through the day Wednesday. 

Dangerous avalanche conditions should persist Wednesday in all elevations bands and especially in the near and above treeline zones. 

Expected avalanches should remain within the near surface storm related weak layers. Watch for evidence of wind deposited snow or pillows. Test for inverted of strong over weak storm snow and give cornices a wide margin.

Loose dry avalanches in non-wind affected terrain will be difficult to manage on steeper slopes. Even a small loose dry avalanche could have unintended consequences such as knocking you off your feet and into a terrain trap. The recent unconsolidated storm snow is now very deep, two to over three feet in places! There was a snow immersion fatality in a tree well in bounds at Snoqualmie on Saturday, and a close call at Crystal Mtn Tuesday, so always travel with a partner. 

Wind slab, storm slab and recent cornices and deep unconsolidated snow are all the key features to plan to avoid in your route-finding and descent routes in the coming days. 

The Christmas snow globe keeps giving here in the PNW! It's gotten very deep out there. Most west slope areas received 1-2 feet in 24 hours ending Tuesday morning! Slightly less in the Mt Baker area, with over 2 feet at Snoqualmie and Crystal areas. Up to 40 inches have accumulated in the past 2 days and 4-6 FEET have fallen in the past five days! 

The most recent observations from professional backcountry observations or professional ski patrol performing avalanche control over the past few days, all indicate the extensive avalanches and avalanche potential are being confined to the most recent storm snow layers. A natural avalanche cycle was reported early Tuesday morning at Alpental, likely a response to heavy showers in the waning convergence zone over Snoqualmie Pass Tuesday morning. These very soft slab avalanches were extensive in number, ranging mostly from 8-12" and did not propagate significantly. Likely releasing down to short lived storm layer weaknesses produced often during variations in snowfall intensities and wind speeds or snow crystal type. 

In the Crystal backcountry Tuesday, observer Dallas Glass made similar observations, noting most avalanche problems were within the shallow storm slab or wind slab formed during Monday's storm. The greatest wind loading and cornice formation was noted on generally east facing terrain near ridges. 

Crystal backcountry near Bullion Basin, shallow (10") skier triggered soft slab, SW aspect, 5800 ft. Released near noon Tuesday, December 22. Photo: Dallas Glass   

The Crystal pro patrol reported similar conditions within the area Tuesday, with numerous storm related soft slabs or wind slabs releasing mostly from 6-12" with a few isolated larger pockets. 

NWAC observer, Matt Schonwald, found increasing wind and storm slab layers forming through the day Monday in the Crystal Mountain backcountry. Multiple test pits on the wind loaded west facing slopes at about 6800 feet showed propagation in ECT tests. Failures ranged from 16-30 inches down on or near the rain event crust formed December 17th. Wind and storm slabs were noted developing at lower elevations on cross loaded terrain features, well below ridgeline.