Avalanche Forecast

Issued: Mar 19th, 2014 9:41AM

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

jlammers, Avalanche Canada

Purcells.

Watch the temperature and solar warming! Heat and cornices are two great ways to shake-up the snowpack over the next couple of days

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

Wednesday night and Thursday: Light snowfall in the north. Up to 15cm in the south / Moderate west-northwesterly winds / Freezing level at 700mFriday: Light snowfall / Light to moderate northwesterly winds / Freezing level at surfaceSaturday: Mix of sun and cloud / Light northwesterly winds / Freezing level at 900m

Avalanche Summary

On Monday explosives control produced several slab avalanches to size 2.5 with a couple reaching the size 3 range. Explosives control also produced cornice fall to size 2. In a nearby region with a similar snowpack a size 3 natural persistent slab avalanche was triggered by solar warming. The avalanche occurred on a south facing slope at 2100m and destroyed timber in the run out.On Tuesday explosives control in the north of the region triggered a size 2.5 deep persistent avalanche which failed on basal facets in unsupported, rocky terrain.

Snowpack Summary

Up to 45cm of settled storm snow has been redistributed into wind slabs in some exposed terrain. These recent storm accumulations sit above crusts on previously sun-exposed slopes and small surface hoar in shaded terrain. Rain from a few days ago has saturated the snowpack at lower elevations and surfaces may now exist as a refrozen crust. Up to 95cm below the surface you may find surface hoar and crusts buried at the beginning of March. This interface is still touchy in some areas, particularly in the north of the region. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been highly variable in terms of reactivity and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Problems

Storm Slabs

Recently formed storm slabs may be gaining strength; however, more recent wind events have likely redistributed surface snow into touchy wind slabs. Watch for triggering in gullies, and in the lee of terrain breaks and ridge crests

Choose conservative lines and watch for clues of instability.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

There are a number of persistent layers in the mid to upper snowpack which have professional operators concerned. These layers, which include recently buried crusts and surface hoar, continue to be touchy, especially in the north of the region.

Dig down to find and test weak layers before committing to a line.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Deep Persistent Slabs

The early February interface is variably reactive and has produced deep and destructive avalanches in a nearby region with recent solar warming. Possible triggers include cornice fall, thin spot triggering or solar warming.

Be aware of the potential for large, deep avalanches.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Mar 20th, 2014 2:00PM