Avalanche Forecast

Issued: Feb 16th, 2017 5:26PM

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

Ruari Macfarlane, Parks Canada

Waterton Lakes.

Travel was Tricky below Treeline on Thursday - our skis repeatedly punched through wet old Storm Slab and crusts, into hollow feeling facets below. The snowpack structure remains less than ideal - dig deep and do snowpack tests.

Summary

Weather Forecast

Snowfall Thursday night (but rain below 1700m) tapers off Friday morning. Friday: Freezing Level 1500m, Clearing trend, Moderate - Strong Westerlies easing.Saturday: Cold initially, freezing level rises to 1700m. Light SE winds, snowfall beginning later.Sunday: Snowfall ending early, sky clearing for a time. Moderate S wind. Freezing level 1700m.

Snowpack Summary

Upto 12mm rain below 1800m Thursday, and more forecast. The upper snowpack is wet below 1800m. Storm slabs are forming up higher. A older, cohesive slab keeps producing Moderate, Sudden test results on a Persistent Weak Layer down 60-90cm (crust on sunny slopes, facets in sheltered areas from 1700-2150m, basal facets in shallow snowpack areas.)

Avalanche Summary

On Thursday, several small-large (Size 1 - size 2) avalanches were observed in steep paths Below Treeline. They were mainly Loose Wet, triggered by steady rainfall. One was a Deep Persistent Slab, releasing on ground in a thin snowpack area. Starting small, it gouged wet snow in its track, finishing large.

Confidence

Forecast snowfall amounts are uncertain

Problems

Storm Slabs

Fresh Storm Slabs are forming, specifically lee to SW winds. These overlie a widespread, stubborn older slab (70cm thick). This sits on a facet-crust combo on solar aspects below 2100m, and on hollow facets (slowly healing) in sheltered/treed areas.

Ride slopes one at a time and spot your partners from safe locations.Dig down to find and test weak layers before committing to a line.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

Several large avalanches have been observed in the front ranges and/or windward terrain, where storm snow fell on shallow facets over ground. Rain on Thursday triggered an avalanche on the basal facets, in a shallow snowpack area Below Treeline.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 4

Valid until: Feb 19th, 2017 4:00PM