Avalanche Forecast

Mostly cloudy conditions Thursday night may not allow for an even re-freeze across the west slopes heading into Friday.  A cooling trend beginning in the north Cascades Friday morning should extend further south during the day, as well as cool easterly winds picking up in the afternoon for the Cascade Passes.  However, periods of sunshine on the west slopes and still moderate snow levels through mid-day will keep wet-loose slides, predominately on solar aspects the most likely avalanche concern. 

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.  If there is a poor re-freeze, look for loose-wet avalanches possible outside the usual daytime heating window. Avoid terrain traps and steep slopes and watch for signs of natural wet loose activity. Near and above tree-line areas should expect weakened cornices along ridges and possible older wind slab on open lee slopes. 

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 relatively mild temperatures again Friday...expect cornices to still be sensitive and likely to fail.

Wind slab has had many days to settle and has been removed from the concerns. The most likely area to still have isolated but still sensitive wind slab would be near Stevens Pass where they experienced a period of moderate easterly winds and colder temperatures earlier in the week. 

Finally the threat of deep slab avalanches with a low likelihood to trigger and high consequence (read deadly) continues. The avalanche danger has been lowered to Moderate to reflect the unlikely nature of this beast and literally means that large avalanches are possible in isolated areas. Moderate danger does not mean the persistent deep slab threat has abated or is of any less consequence, only that it is becoming harder to trigger. Stay conservative and avoid open and exposed avalanche terrain and also be aware of the terrain and parties above your location if you want to minimize this threat. Just because a slope has been skied many times does not mean deeper instabilities aren't lurking and waiting for the right combination of triggers.       

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.

Our impressive 2 week storm cycle ended Monday night. An extended period of freezing rain occurred near Snoqualmie Pass Monday morning and evening producing a locally stout crust. Outside the passes, rain fell up to roughly 4500 feet in the north and 6000-7000 feet in the south Cascades Monday. Moderate east winds reloaded avalanche paths near Stevens Pass Sunday through Wednesday.  

Warm conditions from Tuesday through Thursday have drastically changed the snowpack conditions from recent deep powder snow to wet snow conditions. Significant snow settlement of the upper snowpack has occurred over the last several days. 

Observations for Washington Cascades near and west of the crest

The late January crust layer and associated weak layers are now deeply buried, with many observers in the Snoqualmie Area reporting facet/crust layers of interest 1.5-2 m deep.  While there were many reports from ski areas last weekend of deep slabs down to the crust, the most recent ski patrol reports of explosive triggered slides were from Stevens Pass ski area Wednesday during a heli-bombing mission. In the N-NE facing terrain of Rooster Comb outside the ski area, pro patrol was able to produce 1 very large deep slab of 10-15' that released on a steep and open convex slope.

Warm temperatures and periods of sunny weather lead to an avalanche cycle in the Mt Baker backcountry Tuesday with more skier triggered slides reported on Wednesday. The slides were aided by rapid day-time warming and solar affects on recent storm snow and released on a variety of elevations and aspects with some cornice induced or loose-wet avalanche triggered slab releases as well. On Tuesday, one very large deep slab on the SE aspect of Goat Mountain likely released down to the early February facet/crust critical layer as the crown was estimated at 6-8 ft.  View this photo by Ian Meyer of a skier triggered soft slab on Shuskan Arm Wednesday. 

Several small wet loose slides were reported along the west slopes on solar aspects Wednesday in the Snoqualmie Pass area and in the Stevens Pass area on Thursday. Above freezing temperatures Thursday softened the freezing rain crust around Alpental despite the cloud cover.

A large natural hard slab avalanche released off of steep north facing terrain of Chair Peak near Alpental Saturday and partially caught 3 skiers Saturday. Luckily no on was injured in this potentially deadly avalanche with a 10' crown.

This avalanche paired with the frequent and large results from ski patrol should continue to steer the discussion to terrain management of low probability and high consequence slides that release down to weak layers on or near the late Jan crust. These deep weak layers are unlikely to release by the weight of a skier/rider and likely need a much larger trigger, however as this picture below 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 avalanche terrain. These slides could also possibly be human triggered at a thinner spot in the slab such as near a rocky outcrop.    

  

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. Photo by Patrick Kennedy

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

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