Avalanche Forecast

Issued: Mar 24th, 2017 4:20PM

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

mgrist, Avalanche Canada

South Rockies.

Watch out for fresh wind slabs at upper elevations. Avoid lingering in the runout of avalanche paths as wind loading and cornice fall could trigger large avalanches.

Summary

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

There is significant uncertainty regarding precipitation amounts for Friday into Saturday. Unsettled weather and isolated flurries Sunday onwards. SATURDAY: 5-15cm possible Friday overnight with strong southwest winds. Light flurries easing off throughout the day on Saturday. Freezing level 1600m, alpine temperature around -4 C. SUNDAY: Sunny with some cloudy breaks, moderate southwest wind, freezing level 1700m. MONDAY: Isolated flurries with 2-4 cm possible. Moderate southwest wind, freezing level around 1900 m with alpine temperature around -3 C.

Avalanche Summary

On Thursday, several small Size 1 wind slabs were ski cut on north through east aspects between 1700 and 2200m. Evidence of a large natural avalanche cycle during last week's storm has been reported around the Crowsnest Pass / Sparwood area as well as around Waterton (typically size 2.5 deep persistent slabs). A fresher size 3 avalanche in the Alexander Creek drainage was possibly triggered by a cornice fall on Sunday. Widespread natural activity in the neighboring Kananaskis region suggest conditions may be touchier north of Elkford.Looking ahead, the primary concern is the potential for large deep persistent slab avalanches triggered by natural triggers such as a cornice fall. See the forecaster blog for advice on managing a low probability - high consequence problem (here) and the accompanying photos (here).

Snowpack Summary

Over the past two days we've had 5-15 cm of heavy snow at higher elevations, which sits on a thick hard crust that is quite solid above 1700m. In some locations winds have been strong from the southwest, creating wind slabs on northerly aspects, and isolated features at treeline. Rain has soaked the snow below about 2000 m. Recent rain and sun have left a variety of crusts that are thicker and most supportive in open south facing terrain. Below the new snow and crusts, roughly 50-90 cm of snow sits above the February crust and facet interfaces. In some areas there may still be a poor bond to these interfaces. The bottom third of the snowpack is composed of weak facets and full-depth avalanches over this basal weakness remain a concern.

Problems

Wind Slabs

Strong (southerly) winds will be forming fresh wind slabs throughout the day in the lee of exposed terrain.

Be alert to conditions that change with elevation and aspect.If triggered, wind slabs may step down to deeper layers and result in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

Heavy triggers such as a cornice fall or wind loading are potential triggers for large avalanches on deep weak layers. Stay aware of overhead hazard when traveling at lower elevations.

Recognize and avoid avalanche runout zones.Minimize exposure to sun exposed slopes when the solar radiation is strong.Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 25th, 2017 2:00PM