Avalanche Forecast

Issued: Mar 20th, 2012 10:20AM

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

Avalanche Canada triley, Avalanche Canada

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Snow is expected to continue during the day on Tuesday and taper off during the night, bringing an additional 5-10 cm for the interior regions by Wednesday morning. A weak upper ridge is forecast to build over the southern interior on Wednesday that should cause light southwesterly winds and scattered flurries. There may be periods of sun in the eastern Monashees and Selkirks, and in the northern Purcells. A weak upper trough is forecast to push up from the U.S. border on Thursday bringing moderate precipitation to the southern and Eastern regions. Freezing levels are expected to climb up to about 1800 metres as the trough advances. The upper flow is expected to shift to the southeast with light alpine winds, broken skies with sunny periods, and freezing levels up to 1800 metres in the south and east regions of the interior.

Avalanche Summary

We have one report from Monday of natural avalanches up to size 3.5 on southerly aspects failing down about 100-150 cm on the mid-february persistent weak layer (PWL). Avalanches releasing on this layer are becoming less frequent. Large triggers like cornice fall may initiate a release on the PWL.

Snowpack Summary

Strong southerly winds combined with new snow to develop thin new windslabs in the alpine and at treeline. Sunny breaks on Sunday caused moist snow up to about 2400 metres on solar aspects and up to about 1500 metres on all aspects. The recent storm snow is reported to have settled and bonded in most areas. Recent cornice growth has made cornices unstable. The new snow has added to the well consolidated storm slab that overlies weak surfaces that formed early February. This interface, which lies between 1 and 2 metres below the surface, includes a widespread surface hoar instability that, depending on aspect and elevation, may exist in combination with facets or crusts.

Problems

Wind Slabs

An icon showing Wind Slabs
Recent southwest wind and new snow have developed windslabs in the alpine and at treeline. These windslabs may take a few days to settle and bond.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Cornices

An icon showing Cornices
Cornices are very large. Forecast new snow and strong winds may cause new weak growth that may fall off naturally.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
The mid-February weak layer of facets, surface hoar, and crusts has been buried for about six weeks. Reports of avalanches releasing on this layer are becoming less frequent. Avalanches that do release on this layer may be very large and destructive.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 7

Valid until: Mar 21st, 2012 9:00AM