Avalanche Forecast

Another strong front should spread increasing moderate to heavy precipitation accompanied by very strong crest level winds over the area from the south early Friday.  This weather should rapidly reload avalanche paths that may have already release one or multiple times over the past few days.  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.

The bottom line is this is no time to let your guard down.  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 lead to wet snow avalanche conditions for some areas below tree line. 

Exercise caution Friday and through the weekend by choosing more conservative terrain and avoid travel in avalanche terrain near and above treeline.    

Strong frontal systems are passing across the PNW at a rate about one every day.  The heaviest precipitation in this storm cycle has occurred over the past three days depositing about 50-100 cm of storm snow or 2-3 ft of storm snow over most areas along the west slopes. 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.  

It is those old layers that are the current problem as we have an unusually weak underlying snowpack comprised of a variety of weak layers buried underneath the newest storm snow. Sustained cold temperatures last week caused a varity of weak snow layers including surface hoar or weak near surface faceted snow as well as preserved the generally light amounts of low density snow that fell during last week.  The cold weather also helped to weaken or break down some crust layers in the upper snowpack.  Shifting winds ranging from moderate east winds late last week to strong southerly to westerly winds more recently helped form touchy wind slabs on a variety of aspects near ridges.    

Several widespread natural avalanche cycles have already run their course as reported by WSDOT, ski area professionals as well as professional observers over the past few days with the latest cycle occurring late Tuesday night and early Wednesday during warming and heavy loading.   

Near Mt. Baker, Mt. Baker ski patrol reported a natural cycle down below 5000' with the warming and slides up to 2'.  Some slides reached SR 542 Tuesday night. Alpental ski patrol reported a healthy avalanche cycle Tuesday night as well throughout their uncontrolled terrain with most slides initiated within the new storm snow but reaching down to a localized freezing rain crust was formed Sunday, 2/9. Perhaps the trickiest snowpack continues to be in and near the Stevens Pass area. DOT professionals 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.   

Note the avalanche danger is locally lower in the Crystal Mountain and south region and over in the Olympics 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.