Avalanche Forecast

An exiting warm front should be departing to the east Tuesday with only a chance of a few lingering showers early Tuesday.  However, freezing levels should remain high Tuesday helping to maintain wet surface snow conditions with a likelihood of triggered loose-wet avalanches near and below treeline.  The exception will be the lower Cascade passes, where east winds will limit warming and preserve cold surface snow. 

Above tree-line 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 Tuesday...expect cornices to become more sensitive and likely to fail. 

In the Stevens and Snoqualmie Pass areas where little warming is expected, generally shallow new storm snow from Sunday and Monday are not expected to form extensive new storm slab, but may present dry-loose avalanche concerns on steep slopes and near terrain traps.   

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 Tuesday through Tuesday night and may begin to form shallow new wind slab.    

Human triggered large or very large avalanches have become a low probability but remain a high consequence and thus still relevant especially if smaller slides are able to step down to critical weak layers near or on the late 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.  

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 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 two weeks is about 10-15 inches with snowfall about 8-14 feet at NWAC weather stations near and west of the crest.  

Early Monday morning a period of freezing rain occurred in the Snoqualmie Pass area depositing a thin crust.  This layer should be watched as up to 6 to 8 inches of new snow has accumulated as of Monday evening. 

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 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.

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. 

In the Cascade Passes, continued cold temperatures and light to moderate snowfall Sunday and Monday have re-loaded avalanche paths several times causing DOT to perform multiple avalanche control missions.  These conditions in the passes are maintaining the concern of loose dry avalanches in steeper terrain. 

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.