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West Slopes South - South of I-90 to Columbia River

Issued: 6:04 PM PST Thursday, February 1, 2018
by Dallas Glass

Warm wet weather will develop dangerous avalanche conditions Friday. Avoid steep open slopes at all elevations. Caution should be taken in terrain where avalanches may become large and have significant consequences. 

Danger Scalei
  • No Rating (Info Avail)
  • Low (1)
  • Moderate (2)
  • Considerable (3)
  • High (4)
  • Extreme (5)

Avalanche Problems for Friday

Loose Weti

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  • Aspect/Elevationi
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Wind Slabi

  • Avalanche Problemi
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Forecast for Friday:

Warm wet weather will create dangerous avalanche conditions Friday. Avalanche hazard will be shaped by type and amount of precipitation.

In locations receiving rain, wet avalanche problems will develop. Avoid steep open slopes where you will be able to trigger Loose Wet avalanches. Watch for new roller balls and pinwheels forming on slopes indicating triggering an avalanche is becoming more likely.

Isolated Wet Slab avalanches could occur during periods of higher intensity rain. Wet Slab are extremely difficult to predict and assess. Avoid avalanche terrain if you see signs of slab activity occurring during the day Friday.

In areas receiving snow, winds will build fresh new wind slabs. Avoid steep slopes with wind deposited snow such as below cornices, on wind drifts, and near uneven snow surfaces.

Cornices have grown extremely large over the past week. Be aware and reduce your exposure to cornices overhead. Natural cornice collapse can occur at any time and may trigger avalanche on slopes below.

Less precipitation in some areas Friday will limit the development of avalanche danger.

Avalanche Summary:

Active weather this week has depostited 1-2 feet of settled snow over the 1/29 crust in most locations along the west slopes and the passes. Observations show subtle layers within the recent snow but these layers seem to be gaining strength.

Winds Tuesday redistributed storm snow creating Wind Slabs on a variety of aspects. In many locations large cornices have formed along ridgelines.

Several natural and human triggered avalanches have been reported in the near treeline band over the last few days. These avalanches have occurred on nearly every aspect.

Observations:
Central

Stevens Pass

NWAC Avalanche Forecaster Josh Hirshberg traveled on Lichtenberg Mountain area Thursday. Josh observed 12-18 inches of storm snow well bonded to the 1/29 crust. Winds had drifted snow in the near treeline areas forming shallow wind slabs. Their party triggered a small slab avalanche on a steep convex roll near 5100 feet. Warming air temperatures were beginning to effect surface snow by late in the day.

On Wednesday, an avalanche professional (not ski patrol) was caught in a large  skier triggered wind slab avalanche. The incident occurred in East Highland Bowl around 4800 ft in steep east facing terrain. The crown was 1-2 ft deep, broke wide and caught and carried two skiers already downslope. Thankfully they sustained only minor injuries.

Snoqualmie Pass

Alpental Ski Patrol Thursday reported very large cornices along ridges in the Alpental Valley.

NWAC Pro Observer Ian Nicholson was in the Alpental Valley Wednesday. Ian found wind redistribution of the most recent 8" of snow. Variable snow surfaces were encountered near treeline with wind loading found on a most aspects. In sheltered terrain, storm snow was generally well bonded to the 1/29 crust.

South

An avalanche professional in the Crystal backcountry Thursday noted lingering wind slab instabilities near ridges. By late in the day light rain was already effecting the below treeline bands.

NWAC forecaster Dallas Glass was in the Crystal backcountry Wednesday and found 15" of storm snow generally well bonded to the 1/29 crust. Wind slabs were noted near and just below ridgelines. Cornices have grown large on all exposed ridgelines.  Small skier triggered and natural slab avalanches were noted in steep terrain.

No Corresponding Mountain Weather Forecast Available