Archived

Avalanche Forecast

Apr 7th, 2014–Apr 8th, 2014

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

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

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

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

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 Inland.

The ongoing storm could pack a punch and is driving the Danger Ratings. Persistent weak layers could possibly re-awaken, initiating large and destructive avalanches.

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

As the warm front heads north the associated cold front will move across the region tonight bringing continued light precipitation, extreme to strong SW winds and lowering freezing levels.Monday night: Trace snow amounts. Ridgetop winds strong-extreme from the SW. Freezing levels falling to 900 m. Tuesday: A mix of sun and cloud with some flurries. Ridgetop winds strong from the SW. Freezing levels rising to 1000 m. Wednesday: Light precipitation. Ridgetop winds strong from the SW. Freezing levels near 1000 m.Thursday: Snow amounts 10-15 cm. Ridgetop winds generally light from the SW with strong gusts. Freezing levels 1200 m.

Avalanche Summary

No recent avalanche activity has been reported. A week ago, a steep rocky NE facing feature at 1900m released naturally resulting in a size 3 avalanche. The possibility for large avalanches appears to be still there, and the chance of one is likely to increase with anticipated warming, and/ or localized new loads including precipitation and strong winds on Tuesday.

Snowpack Summary

10-15 cm of new snow fell at upper elevations and up to 30 mm of rain below treeline. The new snow will add to the20 cm that fell last Thursday onto a variety of old snow surfaces consisting of surface hoar, facets and melt freeze crusts. Strong SW winds have likely built new wind slabs on leeward aspects and a poor bond may exist.Below treeline a spring-like snowpack exists including melt-freeze crusts and possibly 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. While it's been mostly dormant, I would not rule out the possibility of it reawakening if we see prolonged warming and/or intense sunshine and new load from snow and rain.

Avalanche Problems

Storm Slabs

New snow driven by strong ridge top winds has likely created touchy slabs. The new snow is not expected to bond well to the current crust/surface hoar combo and natural avalanche activity is likely. Cornices may fail if the sun pokes out.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid lee and cross-loaded terrain near ridge crests.>Extra caution needed around cornices with current conditions.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - 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, a rider finding the sweet spot, or new load from snow/ rain/ wind. Warming and solar influence is also a concern.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Be aware of the potential for large, deep avalanches due to the presence of buried facets and surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 3 - 7

Loose Wet

With warmer temperatures, limited overnight re-freeze and rain forecast, loose wet avalanches are likely. A good indicator of weak snow is wet or moist surface snow, snowballing, and natural avalanches.

Avoid slopes when temperatures rise and the surface snow becomes moist or wet and shows signs of instability, like pinwheels and natural avalanches.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3