Avalanche Forecast

Issued: Mar 6th, 2014 7:28AM

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

Peter, Avalanche Canada

Sea To Sky.

Friday should see a short lull in the weather before another strong Pacific frontal system delivers heavy snow, crankin' winds, and mild temperatures.

Summary

Confidence

Fair

Weather Forecast

Friday: Mainly cloudy with flurries and possible sunny breaks – 3-5 cm. The freezing level remains near 1500 m and ridgetop winds are moderate from the W-NW. Saturday: Moderate to heavy precipitation – 30-45 cm. The freezing level climbs to 1800 m and winds are very strong from the SW. Sunday: Continued moderate or heavy precipitation. The freezing level hovers around 1600-1800 m and winds moderate and gusty from the SW.

Avalanche Summary

I expect a fairly widespread natural avalanche cycle may have occurred on Thursday in response to heavy snow, strong alpine winds, and mild temperatures. Natural activity should taper off a bit on Friday as conditions dry out briefly. Several intentionally skier triggered slab avalanches up to size 1.5 were reported on Wednesday during and after the intense snowfall and strong wind. There was also one accidentally triggered size 1.5 avalanche from a steep wind loaded features that resulted in one rider getting buried up to their chest. A number of loose wet avalanches were also reported during a brief clearing later in the day.

Snowpack Summary

Another 30-60 cm of dense snow has fallen in the past 24 hours, accompanied by strong S-SW winds forming thick wind slabs in exposed lee terrain. This puts the early March melt-freeze crust down 60-120 cm. This melt-freeze crust was found on all aspects at treeline and below, and on all but North aspects in the alpine. Recent snowpack tests give easy to moderate "pops" shears on this layer, and show potential for wide propagation.The mid February crust/facet combo appears to be rounding and bonding in areas where it is buried 150 cm or deeper. Shallow snow pack areas, where the weak layer is buried lass than 100 cm deep, continue to give sudden planar shears in snow profile tests. Big un-supported alpine North aspects are the most likely place to find (and potentially trigger) a well preserved deeply buried February weak layer. Also, be aware of the potential for smaller avalanches to step down and trigger this layer producing a very large avalanche.

Problems

Storm Slabs

Fresh dense slabs have formed in the past couple days, particulary in wind-loaded north and east facing terrain. All this new snow is sitting on a melt-freeze crust buried in early March and was not bonding well initially.

Avoid freshly wind loaded features.>Choose well supported terrain without convexities.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 5

Persistent Slabs

Be aware of the potential for large, deep avalanches.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 7th, 2014 2:00PM