Avalanche Forecast

Yet another strong front should spread increasing moderate to heavy precipitation accompanied by very strong crest level winds over the area Saturday, spreading northward by late morning Saturday and increasing through the afternoon with heavy loading and strong winds.  This weather should once again reload avalanche paths that may have already release one or multiple times during the recent storm cycle .  On such slopes the new storm snow my fall on exposed hard smooth crust layers causing a poor bond and leading to an elevated danger.  Elsewhere, on slopes that have yet to release, such as lower angled terrain and less wind loaded terrain, the addition of increasing rapid load may tip the balance and cause these slopes to release, either naturally or by human trigger.  Some of these slides may be large to very large with destructive potential.

New storm snow may load newly formed crusts as well at mainly lower and mid elevations formed over the past few days. 

Similar snowpack structures around the west have lead to numerous recent fatal avalanche accidents including in NE Oregon on Tuesday. 

Rain at lower elevations at times may maintain the chances of wet snow avalanche conditions for some areas below tree line. 

Exercise caution Saturday and through the weekend by choosing more conservative terrain and avoid travel in avalanche terrain near and above treeline or make this weekend's ski plans towards the ski areas as back country conditions should deteriorate rapidly both Saturday and again Sunday!  

For nearly a week daily frontal systems have crossed the area about one every day.  Storm snow amounts have ranged from 4-8 inches a day over the past two days with previous two days about twice that.  Total storm snow is now in the 1-3 feet range.   Fluctuations in freezing levels with warming at times along with heavy loading rates and very strong winds have all lead to depositing dense storm slab or wind slab over the existing old snowpack layers.  

The variety of existing weak layers preceding this current storm cycle were formed during the sustained cold temperatures in early February and included surface hoar or weak near surface faceted snow as well as preserved the generally light amounts of low density snow that fell around Feb 9,10.     

Several widespread natural avalanche cycles have already run their course over the past several days with the largest cycle occurring late Tuesday night and early Wednesday during the warmest period of the storm cycle along with heavy loading.   

Evidence of widespread natural slab releases have been observed near the Mt Baker area, Stevens Pass and Snoqualmie Pass areas. DOT professionals in the Stevens Pass area reported slides 1-2.5 ft with control work Tuesday morning failing on faceted crystals just above the late Jan crust.  A similar weak layer was involved in a skier triggered avalanche on Big Chief Mtn just outside the ski area boundary Tuesday afternoon around 5000 ft on a NW aspect and resulted in an injury.  NWAC observer Jeff Ward has a great video from Tuesday demonstrating the touchy new storm slab failing on near surface facets and triggering a remote slide near Stevens Pass near treeline and of high quality shears for an increasingly deeply buried layer of surface hoar at lower elevations on a north aspect.

Frontal passages over the past few days have loaded even more storm snow over these potential weak layers or preserved crust layers, including a new crust layer that formed following Wednesday's natural cycle and another new weaker crust now forming up to about 4000 feet due to warming and rain or wet heavy snow. The rain and wet snow created some wet snow avalanches in the Snoqualmie Pass areas as reported by NWAC observer Dallas Glass Friday.  For more evidence of the recent cycle and some excellent suggestions see this short video produced by Dallas Friday the 14th.

These latest crust layers may be bridging over older weak layers and creating new sliding surfaces for new expected storm snow over the next few days. 

A Park Ranger at Hurricane Ridge in the Olympics relayed to NWAC near noon Friday that several people heard a natural avalanche release near Hurricane Hill, likely on a recently loaded N slope, however visibility was poor so no direct observation was made. 

Note the avalanche danger is locally lower in the Crystal Mountain area where there has been less new snow and due to reports of better bonding between old and new snow surfaces in the Crystal Mountain area. 

NWAC observer Jeff Hambelton sent this photo of a storm slab triggered on a test slope at Mt Baker from Feb 10.

Limited snow at the lowest elevations will limit the avalanche danger there. The mid and base pack should still consist of mostly stable crust and melt form layers from periods of warm weather earlier this winter.