Avalanche Forecast

Issued: Mar 23rd, 2014 9:43AM

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

ghelgeson, Avalanche Canada

Purcells.

Sunny breaks on Monday could reactivate weaknesses in the snowpack with the potential for very large natural avalanches.

Summary

Confidence

Fair - Freezing levels are uncertain on Tuesday

Weather Forecast

Synopsis: An upper ridge passes over the region Monday ahead of a pacific frontal system that should force the freezing level to rise under cloudy skies Tuesday. The warming will likely be most dramatic over the Southern Purcells. Look for some precipitation on Wednesday.Monday: Freezing Level: 1000m -1300m; Precipitation: Trace; Treeline Wind: Light, NE | Ridgetop Wind: Light, WTuesday: Freezing Level: 1700m - 2200m; Precipitation: 0:5mm - 0:5cm; Treeline Wind: Light, S | Ridgetop Wind: Moderate, SW Wednesday: Freezing Level: 900m - 1200m; Precipitation: 3:10mm - 4:15cm; Treeline Wind: Light, NE | Ridgetop Wind: Moderate, SW

Avalanche Summary

The Purcell snowpack is a strange beast at the moment:On Saturday an anomalous sized 3.5 avalanche released naturally out of a SE facing feature at 2700m in the central portion of the region. No other activity was reported on Saturday.On Friday while most of the region reported no avalanche activity, a widespread cycle to size 2.5 occurred in the mountains west of Kimberley. Sounds like some of the activity was induced by natural cornice fall.We've received reports of size 2.5 and size 3 natural slab avalanches which occurred a few days ago in the Quartz Creek area. The slides occurred on southwest facing alpine terrain with solar warming as a trigger.

Snowpack Summary

15 - 25cm of light density snow has fallen over the last few days. This snow is settling nicely and likely being formed into soft wind slabs immediately lee of ridge crest.Numerous crust can be found in the upper 30 cm of the snowpack on south facing slopes. These crusts produce sudden collapse failures in snowpack tests. A moderate shear persists down 30 - 50cm on the March 15 crust/surface hoar interface. Down 70 - 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. It also continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, now down 100 - 180cm, seams to be more active in this region than any other in the province and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive. It continues to produce large destructive natural avalanches every few days.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Problems

Wind Slabs

Recent accumulations have likely been blown into pockets of wind slab by generally moderate southwest winds. Watch for triggering in gullies, and in the lee of terrain breaks and ridge crests.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

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 produce sudden failures in snowpack tests.

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

Expected Size

2 - 4

Deep Persistent Slabs

The deeply buried early February interface should stay on your radar as activity on this layer would be large and destructive. 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 24th, 2014 2:00PM