Avalanche Forecast

Issued: Apr 4th, 2014 9:45AM

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

bcorrigan, Avalanche Canada

Purcells.

New snow amounts and rising temperatures are driving the hazard these days. Cornices will become weak as temperature rise. Check out the latest Forecasters Blog.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Synopsis: A slow moving frontal system will bring precipitation into BC.Tonight: Cloudy with clear periods, precipitation should taper off. No overnight freeze and freezing levels up to 1600m. Winds moderate, gusting to strong from the south west.Saturday: Cloudy with flurries. Trace of precipitation, daytime freezing level around 1600m, winds light to moderate from the south west.Sunday: Cloudy with flurries. 5 to 10 cm of precipitation in the forecast, daytime freezing level around 1600m, no overnight freeze, winds, light to moderate from the south west.Monday: Sunny with some cloudy periods. No precipitation in the forecast, freezing levels may climb to 2400 metres, winds light to moderate from the south west.

Avalanche Summary

Reported avalanche activity has slowed down, but there are still reports of cornice failures producing large ( size 2 ) avalanches. Some stepping down to known persistent weak layers. We expect to see natural avalanche activity rise with the precipitation and winds associated with the incoming storm system today and tonight ( Friday ) along with periods of sun and increasing air temperatures later in the week.

Snowpack Summary

The snowpack is highly variable across the forecast region. The last snow fall is well settled now, although there may still be wind slabs on the lee sides of ridge crests mostly north and north east. Moist snow during the day on all solar aspects below 1800 metres, crusts later in the day when the solar aspects become shady, Crust on north aspects in the middle elevations, and surface hoar has formed on protected north aspects.Numerous crusts can be found in the upper snowpack on south facing slopes. A March 15 crust/surface hoar interface is down approximately 50-80cm in most parts of the forecast area. At 60 to 120cm below the surface you may find surface hoar and crusts that were buried at the beginning of March. This interface is still touchy in some areas, and continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, is now down 80 to 180 cm, and still reactive in test pits. An avalanche on any of these deeper, persistent interfaces would be large and destructive. Weak basal facets exist in many areas, but triggering is unlikely, without a big load.

Problems

Wind Slabs

Incoming storm with associated south west winds may build wind slabs on north and eastern lee slopes. Solar aspects can be tricky in the afternoon. Cornices are a big concern with rising temperatures and recent strong winds.

The new snow will require several days to settle and stabilize.>Use ridges or ribs to avoid pockets of wind loaded snow.>Cornices become weak with daytime heating, stay well back from corniced ridges>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

The February and March persistent weak layers could "wake up" if subjected to a large load ie: new snow, a cornice fall, or daytime heating on solar aspects.

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

2 - 6

Valid until: Apr 5th, 2014 2:00PM