Avalanche Forecast

Generally shallow new storm snow from Sunday and Sunday night is not expected to form extensive new storm slab, but may present loose avalanche concerns near terrain traps and sluff management issues in steeper terrain from Snoqualmie Pass and north.  Light amounts of new storm snow Monday afternoon may form denser but shallow storm slab over weaker snow. 

Older wind slab formed last week may still be locally sensitive on lee slopes near and above treeline. Wind transport onto west aspects due to easterly winds near the Cascade Passes should continue Sunday night through Monday and may begin to form shallow new wind slab.    

Human triggered large or very large avalanches have become unlikely but are still relevant and of high consequence if able to step down to poorly bonded previous storm layers or buried persistent weak layers on top of the old January crust. Think before you jump onto an open slope in avalanche terrain where an avalanche releasing down to these depths would be deadly. 

Cornices have grown large and may be sensitive. A cornice failure could provide a large enough natural trigger for a destructive avalanche.   

There's plenty of new snow to go around...continue your careful snow pack evaluation and cautious terrain selection this week.

Recent Northwest Weather

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

Frontal systems over the weekend were weaker than the frequent systems seen over the past 2 weeks.  Until we have an extended break in the storm cycle...the running tally for water equivalent over the past 13 days is about 10-15 inches with snowfall about 8-13 feet at NWAC weather stations near and west of the crest.  An additional 6-8 inches of low density snowfall fell from about Snoqualmie Pass and north through the daylight hours Sunday.

Observations for Washington Cascades near and west of the crest

Several avalanche cycles have been seen in the last 2 weeks. Deep persistent slab remains a concern east of the Cascade crest. Be sure to read the forecast if you venture even slightly east of the crest.

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 northside backcountry terrain Saturday and near Three Way Pk. 

Of even greater concern to backcountry skiers and riders should be a natural wind slab avalanche that occurred near White Pass on an easterly aspect near treeline Friday morning. This natural avalanche produced an 8' crown and underscored NWAC observer Tom Curtis's report from the area Friday of heavy wind loading on lee slopes near 7000 feet (photo below). 

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. 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. 

Light to moderate snowfall along with light east winds Sunday quickly re-loaded avalanche paths near Stevens Pass. DOT had to perform avalanche control several times with loose dry avalanches easily reaching the highway. 

Pictures of a large wind slab avalanche and of large cornice growth near Gunsight Peak, White Pass, Photo by Chris Talbot, Pro Patrol 2-21-14 

 

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.