Avalanche Forecast

Issued: Feb 23rd, 2018 4:19PM

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

Avalanche Canada jmcbride, Avalanche Canada

New snow (possibly up to 20 cm by Sunday) and wind will continue to build slabs and cornices at upper elevations. Sloughing, and cracking around skis and sleds are signs that the new snow is bonding poorly to the old surface.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Light flurries. Accumulation up to 5 cm. Ridge wind moderate to strong, west. Temperature -16. Freezing level valley bottom.SATURDAY: Mainly cloudy, light flurries increasing overnight. Accumulation up to 5 cm. Ridge wind moderate, southwest. Temperature -8. Freezing level valley bottom.SUNDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind moderate to strong, west. Temperature -8. Freezing level valley bottom. MONDAY: Cloudy, flurries. Accumulation trace. Ridge wind moderate to strong, southwest. Temperature -6. Freezing level valley bottom.

Avalanche Summary

On Wednesday a size 2, natural cornice release was reported on a southeast aspect at 1900 m in the northern part of the region.Tuesday there was a report of a skier triggered size 1.5 soft, wind slab release (25-50 cm deep) on a northeast-facing open, treeline slope at 1900 m.Last weekend (Feb 17 & 18),natural wind slab activity to size 3 was reported on south / east aspects from 1250m right up to 2400m elevation, as well as reports of a large avalanche running on a deeply buried weak layer with 1.5m crown and good propagation on east-facing, steep open terrain below treeline. See this MIN post for a good example of these avalanches. Although deeper, persistent avalanche activity has become less frequent over the past week, light triggers in shallow rocky areas, as well as large triggers such as a cornice collapse or step down from a wind slab release, still have the potential to result in large destructive avalanches.

Snowpack Summary

A light dusting of new snow on Friday now covers 20-40cm of storm snow from last week that has been redistributed by previously strong winds creating reactive hard wind slabs in open areas on downwind features. These accumulations overlie an interface that was buried mid-February and consists of; a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, and surface hoar on sheltered slopes.Below the snow surface, several persistent weak layers make up a complex snowpack that is starting to show signs of improving but still remains suspect. In the top 100-150 cm of the snowpack, two surface hoar layers buried in January can be found. Expect to find at least one of these layers on all aspects and elevations.Deeper in the snowpack (150-200 cm deep) is a facet/crust/surface hoar layer from December that is most prevalent at treeline and below.Near the base of the snowpack is a crust/facet combo from late November.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and wind are adding to existing wind slabs in many areas in the alpine, as well as open areas at lower elevations. These slabs vary from soft to hard and have been reactive to human triggers.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Watch for whumpfing, hollow sounds, and shooting cracks.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
Buried weak layers exist within the snowpack and may be reactive to large triggers such as a cornice or wind slab release. Human triggering may also be possible in shallow or thin, rocky, unsupported terrain.
Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Feb 24th, 2018 2:00PM

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