Avalanche Forecast

Issued: Feb 15th, 2013 9:48AM

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

triley, Avalanche Canada

South Columbia.

Forecast new snow is expected to add a new load above the recent storm snow that may cause the buried February 12th weak layer to continue to be reactive.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

Overnight and Saturday: Moderate Westerly winds are expected as the ridge of high pressure flattens and a trough moves into the interior from the Northwest. Alpine temperatures should stay a few degrees warmer than seasonal overnight as the warm front delivers 5-10 cms. Moderate snow fall should start sometime in the early afternoon when the trailing cold front moves across the region. Expect 10-15 cms with cooler temperatures and gusty West winds.Sunday: Unsettled cool air will be left behind as the next ridge of high pressure builds over the interior. Expect light Northerly winds and alpine temperatures down to about -10.0.Monday: Mainly cloudy as the weak ridge of high pressure moves to the East.

Avalanche Summary

The storm slab continued to be reactive on Thursday. Skiers controlled avalanches up to size 1.5 and accidentally released avalanches up to size 2.0. Explosives control in the highway corridor resulted in avalanches up to size 2.5 on North aspects at 2000 metres. There were also a couple of natural cornice falls up to size 2.0

Snowpack Summary

There is a lot of variability in the depth of the new snow slab and the new wind slabs. Areas that received 30-40 cms of new snow have developed thick new wind slabs at higher elevations that may be triggered by light additional loads. The storm slab in these areas has been reported to be reactive to skiers, as it slides easily on a layer of surface hoar that developed just previous to the latest storm. In some areas there is a sun crust that developed during the sunny weather last weekend that is a smooth and fast sliding layer for the new storm slab. Deeper weak layers continue to show planar results in snow profile tests down about 70 cms and also at about 100 cms. These deeper layers are less likely to be triggered by skiers, but cornice falls or other large triggers may step down and result in large avalanches.

Problems

Storm Slabs

A new soft slab is developing above the recent buried crusts, wind slabs, and weak surface hoar crystals. This new slab may be very easy to trigger on steep rolls and unsupported terrain features.

The new snow will require several days to settle and stabilize.>Choose conservative lines and watch for clues of instability.>Avoid steep slopes below cornices.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Wind Slabs

Strong Northwest winds have created thick new windslabs that may be triggered by light additional loads. Wind slab fractures may propagate quickly due to the presence of buried surface hoar and/or sun crusts.

Avoid freshly wind loaded features.>Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

There are older layers of buried surface hoar and crusts that are unlikely to be triggered by the weight of a skier or sledder, but may be triggered by large additional loads like cornice fall or wind/storm slab avalanches in motion.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Feb 16th, 2013 2:00PM