Issued: Mon, Dec 04, 2017 at 10PM

Expires: Tue, Dec 05, 2017

Above 3,500ft High

2,500 to 3,500ft High

Below 2,500ft Considerable

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

BOTTOM LINE

The avalanche hazard has increased to HIGH. Very dangerous avalanche conditions. Travel in avalanche terrain NOT recommended.

Over 16″ of new snow and strong winds gusting 60 mph over the past 3 days have overloaded a fragile snowpack.

Natural avalanches are likely and human triggered avalanches are very likely.

Remotely triggering avalanches will be possible from below or adjacent to slopes 30° and steeper.

Safer terrain includes slopes 25º and less steep, and out of the runout from steeper slopes from above.


PERSISTENT SLAB AVALANCHE PROBLEM

Saturday’s (Dec 2) 12″ of new snow was able to overload and activate persistent weak layers in the mid-pack. This resulted in some natural avalanches reaching an estimated 2 feet deep. On Monday afternoon, snow began to fall again and winds picked up substantially. More new snow with strong winds will continue to overload and activate the persistent weak layers in the snowpack, tonight and tomorrow. Expect avalanches on all aspects, on slopes 30° and steeper, 1-3 feet deep.

STORM SNOW AVALANCHE PROBLEM

During and within 24 hours of the Dec 2 storm, multiple natural storm snow avalanches, approximately 12″ deep, were observed. With a few more inches of new snow and strong winds today, this problem will continue to be active into tomorrow. Natural avalanches are likely and human triggered are very likely on all aspects, 12-14″ deep, on slopes 30º and steeper. Storm snow avalanches will have the ability to step down into the deeper persistent slab problem, increasing the size and consequences of avalanches, up to 2+ feet deep.

WIND SLAB AVALANCHE PROBLEM

Winds on Dec 3 reached a 43 mph max gust and an average wind speed of 16 mph ESE at 4500′. Today, winds picked up again with a max gust of 60 mph and average wind speeds of 18 mph SE at 4500′. Winds were also strong at mid and low elevation. With 12″ – 18″ of available snow for transport from Dec 2 -Dec 4, expect natural avalanche activity 1-3 feet deep, on slopes 30° and steeper, generally, but not limited to, West to North aspects tonight and into tomorrow. Wind slabs will have the ability to step down into persistent weak layers, increasing the size and compounding the hazard.


 

12/3 Storm snow avalanche stepping down into older, persistent weak layers.

12/3 Steep gully terrain trap, with storm snow avalanche. The slope’s steepness was critical here, notice “the avalanche that tried” in the upper right of picture on slightly less steep terrain.

12/3 Lower elevation natural avalanche activity on steep gully sidewall. Be cautious around these steep gully features on the road runs.

12/3 Numerous, larger, natural storm snow avalanches will continue to be a problem through tomorrow.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Avalanche Activity

Numerous natural avalanches Saturday evening and into Sunday. See observations for details.

Recent Weather

Additional Info & Media

The avalanche hazard will remain HIGH this evening and through tomorrow. With snow in the forecast all week, expect the avalanche hazard to remain elevated.

 

 

Posted in HPAC Forecasts.
Jed Workman

Forecaster: Jed Workman