Avalanche Forecast

Issued: Apr 23rd, 2013 8:00AM

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

Sylvia Forest, Parks Canada

Glacier.

VARIABILITY is the main issue right now. Large variation in snow depth across terrain from 20 cm to 2+ meters will make avalanche hazard tricky to assess. Wide swings in temperature will change a solid snowpack to a very weak one.

Summary

Weather Forecast

A weak disturbance in a NW flow will bring mostly cloudy skies today with a chance of convective flurries. A ridge is expected to move in late this afternoon, with clearing skies and rising freezing levels. Note that the wind direction could cause reverse loading in the alpine and along ridge features. Dry conditions are expected on Wednesday.

Snowpack Summary

In the alpine, due north aspects are maintaining dry snow conditions over multiple temperature crusts. Solar aspects have more crusts, and daytime warming is creating sticky, wet, and/or crusty conditions. At lower elevations (below 2200m), the snowpack is largely isothermal, but overnight re-freezing provides firm travel early in the morning.

Avalanche Summary

Large slab avalanches continue to be observed on all aspects. Many of these are associated with cornice triggers, and are failing on the April 3 surface hoar/sun crust PWL, down 40 to 80 cm. Several reports of moist surface sluffing from rocks, or from skiers, have been received. Moist or loose snow avalanches will be very temperature dependent.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Wednesday

Problems

Storm Slabs

20cm of new snow above 1900m may bond poorly to the various surfaces below. Slab avalanches occurred yesterday on slopes receiving direct sun. Solar triggered avalanches are possible today, especially late in the day, as clouds are expected to clear

Avoid travelling on ledges and cliffs where sluffing may have severe consequences.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Wind Slabs

Moderate S-SW winds have transported snow; forming large cornices, deep pockets and isolated windslabs on lee features. They are especially likely in the alpine where winds were highest, and may bond poorly where crusts exist.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Be aware of the potential for wide propagations due to the presence of hard windslabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

Large avalanches failing on deeper weak layers are still being human triggered. They are also sporadically occurring naturally, triggered by windloading, cornice fall and solar warming.

Avoid shallow snowpack areas where triggering is more likely.Be aware of the potential for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

2 - 3

Valid until: Apr 24th, 2013 8:00AM