Avalanche Forecast

Issued: Jan 21st, 2014 8:54AM

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

jfloyer, Avalanche Canada

Cariboos.

If more than 5 cm falls and the wind is strong enough to blow snow around, elevate, alpine danger to Considerable for Wednesday.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain on Wednesday

Weather Forecast

A weak disturbance is expected to bring light precipitation for Tuesday night/Wednesday morning before the ridge rebuilds once again.Wednesday: Expect around 5 mm with the storm overnight Tuesday and into Wednesday morning with ridgetop winds 20-30 km/h from the NW. Alpine temperatures are expected to fall (max of -4C expected) and the inversion temporarily disappears.Thursday: Dry. Alpine temperatures should stay cool, around -4C, but rising late in the afternoon. Ridgetop winds around 20-30 km/h from the NW.Friday: Dry. The inversion returns with an above freezing layer from around 2200 to 3200m. Valley cloud and alpine sunshine likely. Winds 20-30 km/h from the NW.

Avalanche Summary

On Tuesday, two size 2.5 avalanches released on the same slope about 50 m apart. They failed to ground and it is thought that one released naturally and the other released sympathetically in response to the first. These have been the only avalanches reported since Saturday, when a size 2.5 deep persistent slab avalanche was reported to have failed naturally on a southeast facing slope at about 2300m. The avalanche failed on basal facets. On the same day, a snowmobiler triggered what appears to be at least a size 2 slab avalanche form a rocky alpine slope in the Allen Creek area. Little is known about this avalanche.

Snowpack Summary

Snowpack depths vary, but in general there is now 200 to 250cm of snow at tree line and as much as 300 cm in select places in the alpine. In the south and to the east of the region, there are still areas with a relatively thin snowpack. Roughly 100cm of well settled storm snow exists as a stubborn hard wind slab in many areas. Heavy wind scouring is reported to have occurred on many exposed windward slopes. Steep, sun exposed features are most likely seeing a daily melt-freeze cycle while surface hoar has been growing in shaded terrain. Below the recently formed storm slab, you may find surface hoar buried around January 8th, especially on shady slopes below treeline. A basal facet/crust combo (weak sugary snow above and below a crust) near the ground is still a concern in some areas, and was the culprit with some of the very large recent avalanches. Likely triggers at this interface would include cornice fall, rapid temperature changes or thin spot triggering on an unsupported alpine or treeline elevation slope.

Problems

Wind Slabs

Fresh wind slabs are expected in alpine and exposed treeline locations with expected new snow and wind. The bond between the new snow and old surface is expected to be poor.

Be aware of the potential for wide propagations due to the presence of hard windslabs.>The recent snow may now be hiding windslabs that were easily visible before the snow fell.>Avoid freshly wind loaded features.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

Although deep persistent slab avalanches have become less likely, the consequences of a release would be severe. Possible triggers include cornice fall, rapid temperature change or a heavy load over a thin spot.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid convexities or areas with a thin or variable snowpack.>Conditions have greatly improved, but be mindful that deep instabilities are still present.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Jan 22nd, 2014 2:00PM