Avalanche Forecast

Issued: Dec 29th, 2015 7:59AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs, Persistent Slabs and Loose Wet.

jlammers, Avalanche Canada

Northwest Coastal.

Recent winds have been highly variable, and so is the reactivity of recent storm snow. Make observations continually as you travel.

Summary

Confidence

Moderate - Wind effect is extremely variable on Wednesday

Weather Forecast

The current ridge of high pressure will deliver clear skies for Wednesday and Thursday while increased cloud is expected on Friday. An inversion will develop over the forecast period with above-freezing alpine temperatures expected by late Thursday and Friday. Ridgetop winds should be light and northeasterly on Wednesday increasing to strong and southwesterly on Thursday and Friday

Avalanche Summary

Evidence of natural storm slab avalanches to size 2 was observed in the wake of Saturday's storm. Natural avalanche storm slab activity has tapered-off with the current clearing trend. However, human-triggered avalanches will remain a concern for the forecast period, especially at elevations or in parts of the region where recent storm accumulations have settled into a cohesive slab. Small solar-induced loose wet avalanches have also been reported. The likelihood and size of loose wet avalanches will increase with warmer alpine temperatures expected during the forecast period.

Snowpack Summary

Last weekend, between 25cm and 40cm of new snow fell. Wind speed and direction during, and since, the storm have been highly variable. In areas where the wind was strong, there may be a cohesive and reactive storm slab. In areas where the winds were light, you're more likely to find loose powder. The recent storm snow overlies a touchy layer of loose facets and well-developed surface hoar which is reported to exist on most aspects and elevations. Due to the persistent nature of these underlying crystals, newly formed storm slabs may remain reactive for some time. Solar radiation has also come into play, and depending on the time of day, steep solar aspects may be moist or refrozen.Professionals in the region are still keeping an eye on a few other surface hoar layers that developed throughout December which are now buried in the top 100cm. Although these layers may be gaining some strength, they are worth investigating, especially in steep, unsupported terrain.

Problems

Storm Slabs

Up to 40cm of recent storm snow overlies a weak mix of facets and surface hoar. I'd be extra cautious in areas where wind or warming has caused these accumulations to settle into a cohesive slab.

The new snow will require several days to settle and stabilize.>Be cautious as you transition into wind affected terrain.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A few buried surface hoar layers exist in the top 100cm of the snowpack. I would keep these on my radar on steep unsupported slopes, especially at treeline and below.

Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Loose Wet

Temperature inversions and solar radiation forecast for the next few days will promote loose wet avalanche activity, especially on steep, sun-exposed slopes.

Watch for clues, like sluffing off of cliffs, that the snowpack is warming up. >Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be alert to conditions that change with aspect, elevation and time of day.>

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 30th, 2015 2:00PM