Avalanche Forecast

Issued: Mar 10th, 2016 8:08AM

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

jlammers, Avalanche Canada

Purcells.

The timing and intensity of solar radiation on Friday is uncertain. If the sun makes an appearance, the snowpack could destabilize quickly and the Avalanche Danger may be HIGH.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A ridge of high pressure will keep the region mainly dry and sunny for the early part of Friday. Over the weekend a series of frontal systems will make their way across the region bringing 5-10cm of new snow each day. Ridgetop winds will be light on Friday, increasing to moderate and southwesterly for the weekend. Freezing levels will hover around 1500m on Friday, climb to about 1800m on Saturday, and then drop to about 1500m by Sunday.

Avalanche Summary

On Tuesday, several large (size 3) avalanches were reported from south-facing slopes near Golden. The avalanches were thought to be solar-triggered and could have failed on any of the persistent weak layers mentioned in the snowpack discussion section. At the time of publishing no new avalanches were reported, but I'm sure that speaks more to the lack of observations rather than actual conditions. I expect a good round of wind/storm slab activity took place in response to new snow and strong winds on Thursday. I also expect ongoing potential for human triggering on Friday. Sun may also be the driver for avalanche activity on Friday. With that, you can add cornices and loose wet avalanches to the mix. Solar warming will also increase the likelihood of avalanches failing on deeper persistent layers.

Snowpack Summary

Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 30-70 cm recent storm snow overlies a prominent weak layer buried on or around Feb-27. The deepest snow amounts appear to be in the west central area near Kootenay Lake. The Feb-27 weak layer comprises surface hoar and a crust. It has been widely reported but recent snowpack test results are mixed, with some tests indicating this layer is gaining strength, while others indicating it can still fail with sudden "pop" results. A deeper weak layer from mid-February is now down 50-80cm. The early January surface hoar/facet layer is typically down 70-120cm. 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.

Problems

Storm Slabs

Recently formed storm slabs are expected to remain sensitive to light triggers on Friday. Strong winds have encouraged hard slab formation and wide propagations are possible. If the sun comes out on Friday, large loose wet avalanches will be likely.

Be cautious as you transition into wind affected terrain.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A crust/surface hoar layer buried approximately 60 cm below the surface is triggerable by people on sleds or on skis. This layer could also avalanche naturally during periods of solar radiation and produce large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Cornices

Cornices have become large and weak, and may fail naturally with solar radiation forecast for Friday. A cornice fall could also be the trigger for a destructive avalanche on the slope below.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Stay well back from cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 11th, 2016 2:00PM