Avalanche Forecast

Skies should remain relatively clear Wednesday with continued warm temperatures. Freezing levels are expected to remain at about 8000 ft Wednesday and along with sunshine should maintain wet snow conditions with a likelihood of triggered loose-wet avalanches near and below treeline.  Above tree-line areas should expect weakening cornices along ridges and possible older wind slab on open lee slopes. These conditions will warrant careful travel and terrain choices. 

Watch for wet surface snow conditions and given the deep recent storm snow, expect any wet-loose avalanches that start small to possibly entrain large amounts of snow.  Avoid terrain traps and steep slopes and watch for signs of natural wet loose activity.   

Cornices have grown large over the last 2 weeks. A cornice failure could provide a large enough load to trigger a destructive avalanche. With the warming again Wednesday...expect cornices to become more sensitive and likely to fail.  

Continue your careful snow pack evaluation and cautious terrain selections during the work week.

Recent Northwest Weather

An extended mild and dry period occurred the latter half of January generally forming a crust in all areas. Very cold weather followed in early February which produced light low density snowfall, near surface faceting, and faceting near and just above the crust.

Weaker frontal systems last weekend followed the frequent strong storms over the past 2 weeks.  We have finely ended the extended storm cycle as of Monday night, capping off impressive amounts of some 8-15 feet of new snow with a mixture of rain, snow and some freezing rain in the passes.  

Skies have cleared Tuesday with a mix of sun and clouds with temperatures climbing well above freezing with many afternoon temperatures in the lower 40's at NWAC stations away from the passes.  This current warm conditions and rain have drastically changed the snowpack conditions from recent deep powder snow to wet snow conditions. 

Observations for Washington Cascades near and west of the crest

Several avalanche cycles have been seen in the last 2 weeks, including an active avalanche cycle in the Mt Baker backcountry on Tuesday due to rapid warming and solar affects on recent storm snow.  Several triggered and natural slab avalanches released on Tuesday on a variety of elevations and aspects with some cornice induced or loose-wet avalanche triggered slab releases as well.  One very large deep slab released on the SE aspect of Goat Mountain that likely released down to the early February facet/crust critical layer as the crown was estimated at 6-8 ft.  That slide released between 11 am and noon when solar effects were maximized. While the deep persistent slab remains a major concern east of the Cascade crest, it is also evident along the west slopes as well.  These deep weak layers are unlikely to release by the weight of a skier and likely need a much larger trigger, however as this slide shows, a collapsing cornice, warming and sunshine all contributed to tip that balance.  The best way to deal with these conditions remains avoiding large open terrain, as inviting as it looks.  These slides could also possibly be human triggered at a thinner spot in the slab such as near rocky outcrop or a micro terrain feature.  

 

Natural deep slab release (center left) on SE flank of Goat Mtn 2/25 est.crown 6-8 ft.plus numerous fresh loose-wet slides. image Patrick Kennedy

Skier triggered slab on Table Mtn, Tuesday 2/25, fortunately uninjured. Photo, Patrick Kennedy

More natural loose and slab releases on Mt Herman near Mt Baker, Tuesday 2/25. Patrick Kennedy

The late January crust layer and associated weak layers are now deeply buried but continue to produce big results with big explosives by area ski patrol on wind loaded slopes near and above treeline. Perhaps of less relevancy to a backcountry forecast but still plenty interesting is the average 6' crown with a maximum of over 15' Alpental ski patrol was able to produce with large explosives Thursday and again on Friday in their back bowls down to the very slick January crust: Click on Alpental photos one and two.  With large explosives Crystal mountain patrol produced 4-5 ft slides produced while controlling their north-back terrain Saturday and near Three Way Pk. While unlikely to produce a human triggered slide on these deeper weaknesses, it becomes more possible if a larger trigger is involved, such as a large cornice collapse initiating a slide that may break down to this persistent layer.

NWAC Observer Dallas in the Snoqualmie Pass area Friday reported a settling and stabilizing snow pack. He saw possible 30-50 cm wind slab layers on lee slopes and storm slab that was becoming less reactive except on isolated terrain features.  He and other backcountry travelers in the Snoqualmie area over the weekend reported the facet/crust layers to be nearly 1.5 to 2 m deep.

Reports of a very large natural hard slab avalanche off steep north facing terrain of Chair Peak near Alpental partially caught 3 skiers Saturday. Luckily no on was injured in this potentially deadly avalanche with a 10' crown.  It is believed this slide was initiated by a smaller slide or possible cornice failure then stepped down to the deep layer. This avalanche paired with the frequent and large results from ski patrol should steer the discussion to terrain management of low probability and high consequence slides that release down to old storm layers or the late Jan crust. 

The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.

Keep an eye on your riding partner in the deep snow until the new snow settles and the risk of SIS subsides.