Avalanche Forecast

Issued: Mar 16th, 2016 9:13AM

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

South Columbia.

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

On Tuesday, several natural or human triggered wind slabs to size 2.5 were observed on a variety of aspects at treeline and in the alpine. Persistent slab avalanches continue to fail on the late February weak layer. A sledder was killed on Sunday in a size 2 slab avalanche in the Monashees just north of Shuswap Lake. The avalanche occurred on a west facing convex roll at 1830m. The slab was 40-80cm deep, 60m wide and 65m long. The subject was found after more than an hour of probing as rescuers were not able to obtain a transceiver signal. Although this avalanche occurred only a few kilometers north of the regional boundary in the North Columbia region, similar conditions exist in the South Columbias. This was indicated by another avalanche in the southeast corner of the region (see the Mountain Information Network post near Kokanee Glacier). The avalanche, which resulted in a partial burial, was remotely triggered and was in the size 2 range. 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 promoted a melt-freeze cycle on some sun-exposed slopes. 60-110cm 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 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 very large avalanches. Below this interface, the snowpack is generally gaining strength. 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.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 6

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.>Be alert to conditions that change with aspect, elevation and time of day.>

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.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

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