Avalanche Forecast

Issued: Mar 9th, 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, Cornices and Deep Persistent Slabs.

jlammers, Avalanche Canada

Lizard-Flathead.

Storm loading will promote touchy conditions on Friday. Expect the avalanche danger to increase throughout the day.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Thursday night: 10-15cm of new snow / Moderate southwest winds / Alpine temperature of -8Friday: 12-18cm of new snow / Strong to extreme southwest winds / Alpine temperatures of -3 (freezing levels at 1500m)Saturday: Clear skies in the morning with increased cloud in the afternoon / Light southwest winds / Alpine temperature of -3Sunday: Light flurries / Light southwest winds / Alpine temperature of -4

Avalanche Summary

Over the past few days, natural and human-triggered storm slab and loose dry avalanches to size 2 were reported on a variety of aspects. 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 also occurred on a northeast facing alpine slope on Mt Hosmer. The avalanche, which likely occurred on Wednesday, is 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.Looking forward, natural storm slab activity is expected to ramp-up again in response to new snow and wind on Thursday night and Friday.

Snowpack Summary

By Friday morning expect 10-15cm of new snow with lots more falling throughout the day. Strong southwest winds are expected to shift these accumulations into much deeper deposits in exposed lee terrain. The overall storm total for the last week or so now stands at roughly 80-130 cm. At times, strong southwest winds have extensively redistributed the snow forming large brittle cornices. In some areas the recent storm snow is settling into a cohesive slab which sits over a variety of old surfaces including surface hoar, facets, stiff wind slabs, sun crusts, and a rain crust below 1900 m. Little is known about the reactivity of this interface which was buried in the middle of February. Until we get a better feel for it, I'd assume it has 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

On Friday, new snow and wind will form touchy storm slabs which are expected to be most reactive in wind-exposed terrain. Watch for conditions that intensify throughout the day.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very 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.

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

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

Elevations: Alpine.

Likelihood

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 10th, 2017 2:00PM