Avalanche Forecast

Issued: Feb 20th, 2021 4:57PM

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

Tim Haggarty,

Little Yoho.

A significant storm will arrive Sunday. Expect conditions to change during the day. By Monday, a significant step back in terrain choice will be warranted.

Summary

Weather Forecast

Continued light snowfall overnight Saturday as winds reach strong west. Sunday, 15 cm of snowfall is expected as a warm front arrives midday. Freezing levels will approach 1800m and alpine winds will reach 70-80km/h. A cold front Monday will bring up to 35cm of snow, peak winds and cooling as it sweeps N to S.

Snowpack Summary

Extensive wind effect with a few thin wind-slabs and fresh cornice growth developing in the alpine. At treeline and below the snowpack is well settled except the surface snow which is facetted and sluffs in steep terrain although wind effect is starting to creep down. A facet and sun crust layer buried Jan 27 persists at treeline down 30-40 cm.

Avalanche Summary

Moderate wind transport at ridge top led to a least one small cornice triggered avalanche in Kootenay NP today. Sunshine Village reported working with fresh cornice growth and small fresh wind slabs at ridge crests and into isolated treeline areas. Thursday, Sunshine triggered a very large cornice that initiated a size 2.5 persistent slab.

Confidence

Intensity of incoming weather systems is uncertain on Sunday

Problems

Wind Slabs

Winds will be Strong out of the west overnight Saturday and reach Extreme as the storm arrives Sunday. Expect the small wind-slabs in the alpine to develop further and extend to treeline elevations especially as fresh snow and warming temps are added

Use caution in lee areas. Recent wind loading has created wind slabs.
Pay attention to overhead hazards like cornices which could trigger slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Storm Slabs

New snow, intense winds and warm temperatures associated with the storm arriving midday Sunday will promote slab development at all elevations as snowfall continues through Tuesday. Expect the new slabs to be touchy over the current faceted surfaces.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.
The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Feb 21st, 2021 4:00PM