Avalanche Forecast

Issued: Dec 23rd, 2014 7:48AM

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

rbuhler, Avalanche Canada

Sea To Sky.

A storm slab sitting on a touchy weak layer means conditions will remain tricky over the next few days. Continue to make conservative decisions and have a safe holiday.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Conditions on Wednesday will be unsettled as the storm is replaced by a ridge of high pressure that will establish itself for Thursday and Friday. The freezing levels on early Wednesday are expected to drop before the precipitation ends so we may see some snow at lower elevations. By Wednesday afternoon the precipitation should have ended but scattered flurries are possible. Freezing levels should drop to around 800m and alpine winds should taper off to light from the NW. Thursday is expected to be mostly sunny with freezing levels around 700m and light alpine winds. Friday will be similar with a mix of sun and cloud, freezing levels around 800m, and light alpine winds.

Avalanche Summary

On Monday, reported avalanche activity was limited to one natural cornice release that did not trigger a slab as well as loose sluffing from steep terrain. On Sunday, explosive control produced storm slabs size 1-2. On Saturday, reports of natural storm slab activity up to size 2 at treeline and in the alpine. Ski cutting and explosive control also produced numerous storm slab avalanches, some of which stepped down to an old crust layer in the middle of the snowpack. The deepest slab released was reported to be around 1m thick. I expect with the new storm loading on Tuesday and Wednesday morning that we will see new storm slab activity throughout the region.

Snowpack Summary

The new snowfall is sitting on the storm snow from the weekend which is typically 40-60 cm deep and sits above the mid-December crust/facet/surface hoar layer. This layer extends at least up to treeline and possibly lower parts of the alpine. Strong winds over the weekend created wind slabs which may still be a concern and current strong winds will create new wind slabs which will likely be touchy. The November crust is deeply buried near the ground and while triggering this layer is generally unlikely, the likelihood of triggering does increase during the storm with the additional weight of the new snow.

Problems

Storm Slabs

The new storm snow is adding to the storm loading from the weekend. In many areas, these storm slabs are sitting on a touchy weak layer. Strong SW winds are loading leeward slopes in exposed terrain.

Travel in avalanche terrain is not recommended with current conditions.>Use conservative route selection, stick to low angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Deep Persistent Slabs

The increasing load of new storm snow may increase the likelihood of triggering the deeply buried weak layer from early November.

Avoid shallow snowpack areas where triggering is more likely.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Dec 24th, 2014 2:00PM