Avalanche Forecast

Issued: Mar 10th, 2017 5:03PM

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

shorton, Avalanche Canada

Lizard-Flathead.

Dangerous conditions are expected this weekend. New snow and warming will contribute to the storm slab, cornice, and deep slab problems.

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 10-15 cm easing off throughout the day, 30-40 km/h southwest winds, alpine temperatures around -4 CMONDAY: Cloudy with sunny breaks, 40-60 km/h southwest winds, freezing level spiking to 1800 m.

Avalanche Summary

A natural storm slab avalanche cycle occurred on Friday, mostly in the size 2-2.5 range. Storm snow was also reactive to skiers, producing several size 1-2 avalanches on a variety of terrain. Cornices are large and remain easy to trigger. A great image from Sunday illustrates just how surprising the results can be. Click here for details. A size 3.5 deep persistent slab avalanche likely occurred on Wednesday a northeast facing alpine slope on Mt Hosmer. It's thought to have been cornice-triggered and ran a distance of about 900m. This event highlights the isolated, yet destructive, nature of the deep persistent avalanche problem which should become more prevalent as we head into spring.Storm slabs will remain primed for human triggering on the weekend, while the warming trend will increase the likelihood of cornice failures and deep slab releases.

Snowpack Summary

Friday's storm delivered about 25 cm of heavy snow that settled into a touchy slab thanks to mild temperatures and moderate winds. The overall storm total since the start of the month now stands at roughly 70-120 cm. At times, strong southwest winds have extensively redistributed the snow forming large brittle cornices. An interface consisting of surface hoar, facets, stiff wind slabs, sun crusts, and a rain crust below 1900 m was buried in the middle of February. Little is known about the reactivity of this interface, but it may have the potential for large and destructive avalanches. Isolated basal facets still exist in shallow snowpack areas and can produce destructive full-depth avalanches. Likely triggers include intense storm loading, a cornice fall, or strong solar radiation.

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.Be cautious as you transition into wind affected terrain.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Cornices

Cornices are huge and are ripe for triggering. To avoid a nasty ride, give these monsters a wide berth when traveling along ridge crests.

Extra caution needed around cornices with current conditions.Minimize exposure to overhead hazard from cornices.Even small cornice falls may trigger larger avalanches.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

Once or twice a week we get a report of a large naturally-triggered deep persistent avalanche. Likely triggers for these destructive avalanches include storm loading, cornice falls or solar radiation, all of which are expected over the next few days.

Be aware of the potential for large, deep avalanches.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Pay attention to overhead hazards like cornices which could easily trigger deep slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

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