Archived

Avalanche Forecast

Apr 8th, 2014–Apr 9th, 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

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 Inland.

The ongoing storm 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 on Wednesday

Weather Forecast

Another frontal system is targeted for the North Coast Wednesday/ Thursday bringing light-moderate precipitation and freezing levels hovering around 800-1400 m.Tuesday night: Snow amounts 10 cm. Ridgetop winds strong from the SW. Freezing levels falling to valley bottom. Wednesday: Snow amounts 10 cm. Ridgetop winds strong from the SW. Freezing levels rising to 1100 m. Thursday: Snow accumulations up to 20 cm. Ridgetop winds light from the SW gusting strong. Freezing levels near 1300 m.Friday: Unsettled conditions follow the frontal system bringing light precipitation, light SW winds. An approaching upper ridge will gradually start to dry things out later in the day.

Avalanche Summary

A widespread natural avalanche cycle up to size 4 occurred on Monday. I suspect natural avalanches will continue through the forecast period, however size and magnitude may decrease with cooler temperatures.

Snowpack Summary

20-30 cm of new snow fell at upper elevations and up to 40 mm of rain below treeline. The new snow fell onto a variety of old snow surfaces consisting of surface hoar, facets and melt freeze crusts. Strong SW winds have likely built thick wind slabs on leeward aspects and a poor bond currently exists.At lower elevations (Some treeline and below treeline), the snowpack is moist and/ or wet, saturated and weak. Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm. The early February crust/facet/surface hoar combo is down 150 - 200cm. Recently, these layers have become overloaded with the new load from snow, rain and warmer temperatures. They must remain on your radar.

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 are large and weak.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 7

Loose Wet

With warmer temperatures, limited overnight re-freeze and rain forecast, loose wet avalanches are likely.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3