Avalanche Forecast

Issued: Mar 20th, 2013 8:13AM

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.

Parks Canada Sylvia Forest, Parks Canada

Cornices are large and unsupported.  A few have failed recently, causing large avalanches.  The new storm snow will be a concern everywhere, however solar aspects are most problematic due to buried sun crusts.

Summary

Weather Forecast

A low will bring increasing precipitation today, with most intense accumulations occurring mid-day.  Upslope (westerly) locations will receive locally heavy amounts, accompanied by strong southerly winds.  Freezing levels will rise to 1300 m today, and drop tomorrow as a cold front follows.  Unsettled conditions will remain for tomorrow and Friday.

Snowpack Summary

Storm snow slabs exist in the alpine, but are sporadic.  Reports from north aspects (Dome Glacier) indicate the upper snow is well bonded; however avalanches to size 2.5 were observed yesterday from solar aspects in the Connaught drainage.  Where storm slabs rest on a buried suncrust-surface hoar combo (March 11), wide propagations can be expected.

Avalanche Summary

Numerous slabs were seen yesterday, mostly in the top 30-40cm.  Skiers on Mt. Sifton yesterday were able to cut a cornice to check the slope, and released a size 2.5-3 avalanche on a south aspect, 40cm deep x 100m wide.  Another size 2.5-3 slab was seen in the Asulkan drainage on Mt. Abbott. 

Confidence

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

Problems

Storm Slabs

An icon showing Storm Slabs
Another 8-10cm of snow overnight has added load to last weeks storm interface.  More snow, moderate winds and warm temps today will add to this problem, especially on solar aspects where buried suncrusts are providing good failure planes.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Avoid steep slopes below cornices.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Wind Slabs

An icon showing Wind Slabs
Isolated wind slabs in the alpine and near ridge crests surprised a few skiers yesterday.  These failures could break down to deeper instabilities.  Cornices are very large and unsupported.
Be careful with wind loaded pocketsAssess start zones carefully and use safe travel techniques.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
It will likely take a large trigger, like a cornice or another avalanche to trigger the surface hoar/crust layer from February 12, now down 1-1.5m. The resulting avalanche would be very large and destructive if triggered.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Mar 21st, 2013 8:00AM