Avalanche Forecast

Varied cloud cover Wednesday night may produce an uneven re-freeze of the snow surface. There should be a few hours of partly sunny weather for the central and north Cascades through mid-day Thursday along with slightly cooler temperatures and snow levels. However, near the Cascade Passes (especially near Stevens Pass where there isn't a thick ice crust) a break in the east winds should actually cause warmer temperatures in the below and near treeline zones. Despite the gradual cooling trend Thursday away from the Passes...wet-loose avalanches will still be a concern Thursday through the west slopes and even more so in areas that did not see much warming Tue/Wed. 

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 weakening 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 mild temperatures again Thursday...expect cornices to become more sensitive and likely to fail.

Finally the threat of deep slab avalanches with a low likelihood to trigger and high consequence (read deadly) continues Thursday. Stay conservative and avoid open and exposed avalanche terrain and also be aware of the terrain above your location. 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.

We have finally exited our 2 week storm cycle as of Monday night, tallying up impressive amounts of 8-15 feet of new snow during this span. An extended period of freezing rain occurred near Snoqualmie Pass Monday morning and again Monday afternoon producing a locally stout ice 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 again and again near Stevens Pass Saturday night through Wednesday.  

Periods of sunshine and warm temperatures Tuesday and Wednesday pushed highs into the upper 30s to 40s away from the locally cooler Cascade Passes. The warm conditions and rain have drastically changed the snowpack conditions from recent deep powder snow to wet snow conditions in these areas. 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 most recent avalanche cycle occurred in the Mt Baker backcountry Tuesday with more skier triggered slides on Wednesday aided by rapid day-time warming and solar affects on recent storm snow.  Stevens Pass DOT consistently saw their avalanche paths reloaded by moderate easterly winds transporting new snow with slides regularly covering the highway during planned closures as well as evidence of very large natural slides starting from about Sunday through Wednesday morning.   

Despite an active period on Tuesday, skiers still triggered a sensitive soft slab off of Shuskan Arm Wednesday right outside the ski area. View this photo one by Ian Meyer. 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 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. Deep persistent slab is a concern on both sides of the crest. 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, as inviting as it looks. 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

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

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

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. Alpental ski patrol produced slides averaging 6' with a maximum of over 15' with large explosives Thursday and again on Friday in their back bowls releasing down to the very slick January crust: Alpental photos one and two.  With large explosives Crystal mountain patrol produced 4-5 ft slides while controlling their north-back terrain Saturday and also near Three Way Pk. 

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.