Avalanche Forecast

Issued: Apr 4th, 2018 4:01PM

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

jonas hoke, Parks Canada

Jasper.

Good skiing can be found in sheltered terrain.Persistent weak layers continue to show isolated signs of reactivity, this problem will likely persist for some time.

Summary

Weather Forecast

A westerly flow in the upper atmosphere is pushing a series of weak frontal systems over our area, giving cool temps and light flurries.Up to 5 cm of snow will fall overnight into Thursday, with moderate SW ridgetop winds (tapering to light mid-morming). Alpine temps will be cold, with an overnight low of -18C, and a daytime high of -10C.

Snowpack Summary

Recent storm snow has been blown in to a wind slab up to 30cm thick. This has added to the previous slab sitting on a sun-crust on solar aspects and facets on polar aspects - these are now buried as deep as 60cm. Underneath the variable slab in the upper snowpack, as well as in shallow areas, the snowpack is generally facetted and weak.

Avalanche Summary

On Tuesday, avalanche control at Marmot Basin using explosives produced several size 2 slab avalanches. These were on Northerly alpine slopes, and failed on persistent weak layers. A recent MIN report from the Bald Hills has a good photo of an avalanche that occurred on an alpine NE aspect (from the photo it looks to have been skier triggered).

Confidence

Due to the number of field observations

Problems

Persistent Slabs

Persistent slabs sit on facets on polar aspects (more reactive recently), and a hard melt-freeze crust on solar aspects. Use a cautious approach in open terrain and assess the bond at these interfaces carefully before committing to a slope.

Avoid shallow snowpack areas where triggering is more likely.Watch for signs of instability such as whumpfing, or cracking.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Wind Slabs

In most cases this interface presents as a manageable surface instability and is expected to go dormant pretty quickly.

Use caution on open slopes and convex rolls If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Cornices

Cornices continue to grow with fresh snow and wind. Several failures were noted in the past week, in most cases triggering a slab below.

Give cornices a wide berth when travelling on or below ridges.Minimize exposure during periods of loading from new snow and wind.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Apr 5th, 2018 4:00PM