Avalanche Forecast

Issued: Jan 14th, 2013 10:25AM

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

ghelgeson, Avalanche Canada

Purcells.

I’ve based this forecast on a weather model that shows rapidly increasing alpine temperatures on Tuesday. If it doesn’t warm up, then these danger ratings are one notch too high. See the forecasters blog for warming details.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Tuesday: Winds out of the NW at extreme values. Freezing level rising to 2500m+ around lunch time.Â No snow/rain. Clearing skies.Wednesday: Freezing level stays high around 2300m.Â Strong/Extreme NW winds persist.Â No precip expected.Thursday: Freezing level comes down to 2000m.Â Winds switch to westerly strong.Â Increasing to westerly extreme in the afternoon.

Avalanche Summary

Most of the region did not see any activity on Sunday. The exception was around the bugaboos where several natural size 2.5's came out of the alpine on a piece of west facing terrain.Â

Snowpack Summary

40 - 90 cm of settled storm snow rests on the January 4th interface which consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas and sun crust on steep south and west facing slopes. This interface has gained a significant amount of strength.Â The concern is that it will spring back to life when the warm temperatures and direct solar come into play midweek. Recent tests on this interface show shears trending towards Resistant Planar. Professionals operating in the region are most concerned about slopes that have not yet avalanched. Wind slabs formed during the last storm are getting old and tired.The deep crust/facet combo from early November is till evident but it is inactive at this point.?

Problems

Wind Slabs

NW winds are forecasted to be screaming (extreme) at ridgetop. Watch for wind slab formation in exposed terrain in both the alpine and treeline vegetation bands.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

I suspect this layer will spring back to life when the warm temps and sunshine come out Tuesday. Slopes that didn't slide in the last cycle are of particular concern. Pull back to simple terrain without overhead hazard as soon as it warms up.

As the sun comes out and the temperatures rise the potential for large avalanches failing on the buried surface hoar will quickly increase.>Avoid traveling on slopes which are becoming wet due to sun and warm temperatures.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Valid until: Jan 15th, 2013 2:00PM