Avalanche Forecast

Issued: Mar 10th, 2017 5:37PM

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

shorton, Avalanche Canada

South Rockies.

Dangerous conditions are expected this weekend. New snow and warming will contribute to the storm slab and deep slab problems. Conservative terrain choices are essential.

Summary

Confidence

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

Weather Forecast

SATURDAY: Clear skies in the morning with increased cloud in the afternoon and light flurries, 30-50 km/h southwest winds, alpine temperature around -6 C.SUNDAY: Overnight snowfall of 5-10 cm easing off throughout the day, 30-40 km/h southwest winds, alpine temperatures around -4 CMONDAY: Chinook conditions, cloudy with sunny breaks, 50-70 km/h winds, freezing level spiking to 2000 m.

Avalanche Summary

Reports from Friday include several size 2 natural storm slabs in steep northerly terrain and numerous ski cut storm slabs in the size 1-1.5 range (and one size 2 skier triggered avalanches). Storm slabs will likely remain reactive to human triggers over the weekend.On Thursday, explosive avalanche control along the White River (in the northwest corner of the region) produced over 10 deep persistent slab avalanches releasing on basal facets. Most of the avalanches were size 3, included several than ran full path to valley bottom taking mature forest and blocking the river with up to 8 m of debris. An older size 2 natural avalanche failing on basal facets was also reported in the Crossing Creek area. Looking ahead, dramatic warming will likely wake up the deep persistent slab problem and create the potential for very large avalanches.

Snowpack Summary

Friday's storm delivered about 15-30 cm of heavy snow that settled into a touchy slab thanks to mild temperatures and moderate winds. Strong southwest winds are expected to shift these accumulations into much deeper deposits in exposed lee terrain. The overall storm total since the start of the month now stands at roughly 50-90 cm. In some areas, the resulting slab may have a poor bond to the old snow interface which consists of stiff wind slabs, crusts, and facets. The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above this weak layer of sugary, rotten facets that developed in December. This remains a concern and should be on your radar, especially with the recent loading and upcoming warming.

Problems

Storm Slabs

Fresh storm slabs formed on Friday and will remain reactive to human triggers throughout the weekend. They'll be extra touchy in wind-exposed terrain.

Be alert to conditions that change with elevation and time of day.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

Recent activity on deep layers suggest deep persistent slabs should be on your radar. Likely triggers include storm loading, cornice falls or solar radiation, all of which are expected over the next few days.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Avoid steep convexities or areas with a thin or variable snowpack.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 11th, 2017 2:00PM