Avalanche Forecast

Issued: Jan 4th, 2014 8:56AM

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

Avalanche Canada ghelgeson, Avalanche Canada

While humans crave simplicity the current situation is anything but. The answer to the avalanche problem this weekend is staying conservative with terrain selection.

Summary

Confidence

Fair - Freezing levels are uncertain on Monday

Weather Forecast

A strong, stable northwesterly flow will prevail over the province while a strong upper ridge remains offshore. The mountain top winds should ease Sunday as the upper ridge moves over the coast. The ridge will then weaken somewhat on Monday but will still protect the province from Pacific systems.Sunday: Freezing Level: Valley Bottom; Precip: Nil; Wind: Light, Variable. Strong NW at ridgetop.Monday: Freezing Level: Valley Bottom with chance of an Above Freezing Layer from 1500 2500m. Precip: Nil; Wind: Light Variable, Mod NW at ridgetop.Tuesday: Freezing Level: Valley Bottom; Precip: Trace; Wind: Lht Variable.

Avalanche Summary

Lot's of avalanche activity on Friday as the snowpack adjusted to the new load. Avalanches were running naturally to size 3.5 with many reports of runouts filled with debris. Skiers triggered avalanches both intentionally and accidently to size 2.5. Sounds like the long propagations across small terrain features surprised a few folks. While the large avalanches likely dug into deeply buried weak layers, it appears as though much of the activity was limited to the storm snow or the mid December surface hoar. Saturday's clear skies should provide great visibility and more insight into the latest avalanche cycle.

Snowpack Summary

Thursdays storm delivered 20 - 50 cm of new snow bringing the average regional depth to 160 - 240cm.This new snow lies on top of old wind slabs, a thin melt freeze crust below 2100m and numerous weak layers. Down 40 -100cm is the mid December layer comprised of surface hoar, stellars and/or a crust. Around 70 -140cm down is the early December surface hoar, faceted snow and/or crust.There are two deeper layers of note. The late-November persistent weak layer consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas and is now buried 90-160cm below the surface. The October deep persistent weak layer consists of a layer of facets sitting on a crust at the base of the snowpack. This layer is predominantly found on northerly aspects at treeline and in the alpine. The depth of both these layers makes directly triggering an avalanche on them unlikely (maybe a heavy load on a thin spot in steep terrain). Their presence could, however, increase the size of a potential avalanche through step-down.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and fresh wind slabs lie over two different persistent weak layers in the upper meter of the snowpack. Wind exposed lee slopes at and above treeline will likely remain touchy Sunday.
Avoid freshly wind loaded features.>This problem will take extra time to settle out given the presence of persistent weak layers.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

An icon showing Persistent Slabs
The presence of persistent weak layers increases the likelihood of larger avalanches that could release to a depth of a meter or even more. The distribution and reactivity of persistent weak layers is highly complex at the present time.
Choose well supported terrain without convexities and avoid slopes with a thin or variable snowpack.>Resist venturing out into complex terrain, even if you observe no obvious signs of unstable snow.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Valid until: Jan 5th, 2014 2:00PM