Avalanche Forecast

Issued: Jan 20th, 2013 4:00PM

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

garth lemke, Parks Canada

Jasper.

For Monday-Tuesday, if sun is intense and freezing levels rise rapidly, expect initiation potential, danger rating, and solar impacts to increase in the afternoon especially S aspects. Good skiing is hard to find so let us know if you found some.

Summary

Weather Forecast

Ridge of high pressure may shift slightly East allowing well above normal temps for Monday - Tuesday; however, there is low confidence in this. It will be cold at night and warming during the day. Monday-Tuesday will be mainly sun, NW40-70 ridge winds, 2000m afternoon freezing level. Wednesday will bring light snow and trending colder temperatures.

Snowpack Summary

Extreme NW winds stripped alpine to tree line fetch zones. Hard slabs are present on all lee slopes tree line and above. Surface hoar is found 10-40cm down depending on wind-loading patterns. Weak basal facets dominates thin snowpack areas. Below tree line, the old storm snow is over a rotten facet base. Colder temperatures helping stability.

Avalanche Summary

On Friday, numerous full depth natural slab avalanches occurred on thin, steep, lee alpine slopes. In the days preceding, we were seeing up to size 3 from wind loading. They ran far in paths with steep run outs. No new avalanches were observed on Saturday. No patrol occurred on Sunday.

Confidence

Freezing levels are uncertain on Monday

Problems

Wind Slabs

Extreme winds have developed hard wind slabs on a variety of lee aspects. It sporadically overlies a buried surface hoar from Jan 6th. Natural avalanches were initially observed on thin, steep, lee slopes in the alpine but now subsided.

Be careful with wind loaded pockets while approaching and climbing ice routes.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

Unlikely - Possible

Expected Size

1 - 3

Deep Persistent Slabs

Initiating the surface slab can trigger this deeper weakness. This will more likely occur in shallow snowpack areas. Less activity last 2 days due to cooler temperatures but expect some steep slopes where human triggering remains possible.

Be aware of thin areas that may propogate to deeper instabilites.Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 21st, 2013 4:00PM