Avalanche Forecast

Issued: Mar 16th, 2016 9:07AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Persistent Slabs, Loose Wet and Cornices.

jlammers, Avalanche Canada

Purcells.

As stormy weather tapers-off and a dry ridge builds over the province, solar radiation will become the driver for natural avalanche activity. Watch your overhead hazard as avalanches could travel farther than anticipated.

Summary

Confidence

High

Weather Forecast

A dry ridge of high pressure will develop over the region bringing clear skies for Thursday and Friday. Increased cloud is forecast for Saturday. Ridgetop winds will be light to moderate from the northwest on Thursday morning, and then become light for the rest of the forecast period. Freezing levels will hover around 1200m on Thursday, 1500m on Friday and 2100m on Saturday.

Avalanche Summary

Explosives control on the west/central part of the region produced slab avalanches to size 3 on Tuesday. In many cases, avalanches failed within the recent storm snow; however, a few of the bigger avalanches stepped down to the late February weak layer. A size 2 persistent slab avalanche was also noted on Sunday in the Dogtooth Range. The avalanche, which failed on a northeast aspect at 2200m, started as a smaller wind slab and stepped-down to the late February layer. This illustrates the touchy conditions in some areas. As stormy weather tapers-off and a dry ridge builds over the province, solar radiation will become the driver for natural avalanche activity.

Snowpack Summary

On lee features at treeline and in the alpine light amounts of new snow overlie older wind slabs while intermittent sunny skies have likely promoted a melt-freeze cycle on some sun-exposed slopes. 35-80 cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer, which was buried on February 27th, seems variably reactive. In other words, it's still really touchy in some places while in other places it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential for large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger or significant warming. At ridgetop, cornices are huge and could be become increasingly touchy with forecast solar radiation.

Problems

Persistent Slabs

The late February layer is becoming less likely to trigger, but it continues to surprise riders with large avalanches. I'd aim for well-supported slopes without convexities, and I'd be increasingly cautious as solar radiation comes into play.

Choose well supported terrain without convexities.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 5

Loose Wet

As the sun comes out, surface avalanche conditions will include a mix of wind slabs in high elevation lee terrain, and pushy loose wet activity on steep, sun-exposed slopes. Loose wet avalanches may also trigger deep and destructive slab avalanches.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Sluffs may trigger deeper instabilities.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Cornices

Daytime warming and solar radiation will promote large cornice failures which could, in turn, trigger a large avalanche on the slope below.

Pay attention to overhead hazards like cornices.>Stay well back from cornices.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Mar 17th, 2016 2:00PM