Archived

Avalanche Forecast

Apr 7th, 2014–Apr 8th, 2014

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

4: High

The avalanche danger rating at treeline will be high

Below Treeline

4: High

The avalanche danger rating below treeline will be high

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

4: High

The avalanche danger rating at treeline will be high

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Regions: Northwest Coastal.

The ongoing storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.

Confidence

Good

Weather Forecast

As the warm front heads north the associated cold front will move across the region tonight bringing continued heavy-moderate precipitation, extreme to strong SW winds and lowering freezing levels.Monday night: Snow amounts up to 15 cm. Ridgetop winds strong-extreme from the SW. Freezing levels falling to 600 m. Tuesday: Snow amounts 10-15 cm. Ridgetop winds strong from the SW. Freezing levels rising to 800 m. Wednesday: Snow accumulations up to 30 cm. Ridgetop winds strong from the SW. Freezing levels near 700 m.Thursday: Moderate precipitation for coastal areas, and light inland. Ridgetop winds generally light from the SW with strong gusts. Freezing levels 1000 m.

Avalanche Summary

Expect a widespread natural avalanche cycle to continue at all elevations on Tuesday. It will take a couple of days before things start to settle out. Travel in avalanche terrain is not recommended.

Snowpack Summary

Up to 30 cm (25-35 mm) of new snow fell overnight Sunday at upper elevations forming new storm slabs. Strong southerly winds has transported the new snow building thick wind slabs on leeward features and potentially overloading persistent weak layers that exist lower in the snowpack. I suspect cornices have grown large. At lower elevations the snowpack will likely become saturated adding to the already spring-like isothermal conditions.Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds.

Avalanche Problems

Storm Slabs

New snow driven by strong ridge top winds will likely build thick storm and wind slab problems at and above treeline. The new snow will likely have a poor bond and is expected to be unstable initiating large-very large avalanches.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Very Likely

Expected Size: 1 - 5

Deep Persistent Slabs

Two buried weak layers exist in the snowpack. These weak layers could be activated by cornice fall, a surface avalanche in motion, or intense loading from snow, rain and wind. Avalanches failing on these weak layers will be large and destructive.

There is potential for large, deep avalanches due to the presence of buried facets and surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 7

Wet Slabs

At lower elevations the snowpack will likely become saturated and weak with heavy rainfall. Wet slab avalanches typically move slower, however they are very destructive and can mow down anything in their path.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid run-out areas, road cut banks and steep slopes at treeline and below. Indicators of the snowpack becoming moist or wet is snowballing, larger pinwheels and of course natural avalanche activity. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4