Issued: Thu, Apr 06, 2017 at 8AM

Expires: Sun, Apr 09, 2017

Strong solar heating will quickly increase the danger of wet slabs below treeline, and cornice fall and dry slabs above treeline during the heat of the day. Remember that we still have a deep persistent weak layer 1m down and include a wide safety margin to manage the uncertainty.

Above 2,500ft Considerable

1,500 to 2,500ft High

Below 1,500ft Low

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Problem #1: Wet Avalanches

Distribution: Sunny aspects between 1500 and 2500ft, during times of strong solar heating. We’ve had enough rain and melting in this elevation band to cause water to run through the snowpack, and the danger of wet slides will increase to high during the heat of the day. Plan to be off steep solar aspects before the sun has time to soften the snow and cause melting.

Problem #2: Storm Snow

Distribution: West-North-Northeast aspects above 3500ft. Last night’s new snow was blown around by SE winds, building fresh wind slabs at the top of the snowpack. Any cohesive, slabby areas of new snow will be sensitive to human weight. Be especially careful of this on wind loaded slopes steeper than 30 degrees. As the sun warms the new snow the danger of storm slabs and possibly wet slabs will increase. Avoid steep slopes with strong solar radiation.

Problem #3: Falling Cornice

Cornices built by south winds throughout the season are going to start sagging and weakening now that the snowpack is warming up. We’ve reached that time of year when they start dropping and collapsing frequently. Give cornices a wide berth…stay as far away from them as possible while traversing ridgelines, as they tend to break much farther back onto a ridge than expected. Cornice/snow ledge collapse has caused serious accidents and even a fatality in the last few years.

Problem #4: Deep Slab

Distribution: All aspects above 2500ft. About 1 meter deep, we have hard slab with weak, facetted snow underneath. There’s also an old rain crust below acting as a slick bed surface. This weak layer has started to slowly strengthen, but the weakness still exists. Heavy triggers like cornice drops, snowmachines, or small avalanches may trigger this stubborn weak layer and cause large, destructive hard slab avalanches. The low-probability, high-consequence nature of deep slab instability require conservative decision making and a wide risk-margin. Think about where your “safe zones” are, and what could happen if the slab breaks wide enough to take out your safe zone. 

Recent Avalanche Activity

Last week’s avalanche activity included several D3 slides, running about a meter deep on the troublesome Early March facet layer. This includes some slides that have been remotely triggered from ridgelines, and some skier-triggered slides and close calls.

Recent Weather

About 10″ of new snow fell above the snow level (~2500ft) last night. South winds were strong. Clouds are clearing out Thursday, and partly cloudy skies with strong sunshine will continue Friday and Saturday. Sunday morning will be cloudy, but may clear out by afternoon. Alpine temperatures will be rising to the mid-upper 30’sF during the heat of the afternoon each day.

Snow levels Wednesday were about 3500ft, with .2-.5″ of precipitation.

Additional Info & Media

We’ve been getting widespread reports of sketchy conditions for the last several days. This includes lots of whumphing, shooting cracks, and fresh avalanche activity. Be conservative, and avoid avalanche terrain when possible.

Posted in Transitional Zone Forecasts.
Erik Stevens

Forecaster: Erik Stevens