Avalanche Forecast

Issued: Feb 27th, 2016 7:45AM

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

pmarshall, Avalanche Canada

South Columbia.

Forecast snowfall and wind on Sunday could build fresh and touchy wind slabs in exposed terrain. Choose your lines carefully and avoid exposure to terrain traps.

Summary

Confidence

Moderate

Weather Forecast

Sunday: Cloudy with light snow 5-10 cm. The freezing level is around 1400-1500 m. Ridge winds are moderate from the S-SW. Monday: Up to 10 cm overnight then cloudy with sunny breaks and a chance of flurries. The freezing level rises to 1200-1400 m during the day. Ridge winds are light. Tuesday: A mix of sun and cloud. The freezing level jumps up to 1500 m and winds remain light.

Avalanche Summary

Avalanche activity on Friday mainly consisted of loose wet or dry sluffs (depending on aspect) and natural cornice falls. There was also a few reports of natural and skier-triggered wind slabs up to size 1.5 in exposed north-facing terrain. On Thursday, natural and skier-triggered persistent slab avalanches were reported as well as large natural cornice releases and loose sluffing up to 2.5 on solar aspects. A skier triggered a size 2 slab on a northeast aspect convexity at 2150m which released on the February 21 surface hoar layer down 40cm. Two size 1 soft slab avalanches were reported from a northwest aspect which released down 20cm on a layer of surface hoar (buried Feb. 21). A couple natural cornice falls also triggered size 3 persistent slabs on north-facing slopes in the alpine.

Snowpack Summary

Up to 10 cm of new snow sits on a sun crust on solar aspects and surface hoar on shady and sheltered slopes. This new snow may have undergone a melt-freeze cycle on solar aspects on Saturday. New wind slabs are expected to form over the weekend with forecast moderate southwest winds in the alpine. A weak layer of surface hoar and/or a sun crust buried February 21 can be found 15-60cm below the surface. This layer is reported to be increasing in reactivity in the deeper snowfall areas as the week old storm snow continues to settle into a cohesive slab with recent warm temperatures. The surface hoar and/or crust layer which was buried February 10 is now down 60-100cm and has been responsible for some very large avalanches recently. This layer is expected to become much less reactive over the weekend with cooling temperatures. Large cornices have recently been a concern but should also gain strength will colder temperatures.

Problems

Wind Slabs

Fresh wind slabs may develop with forecast snowfall and moderate southwesterly winds. An underlying sun crust or surface hoar layer may increase the reactivity of these slabs.

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

The likelihood of triggering the weak crust/surface hoar layer down 50-90cm is decreasing with colder temperatures. In the Monashees, a patchy layer of surface hoar down 30-40cm may still be reactive to skier triggering.

Minimize exposure to sun exposed slopes when the solar radiation is strong.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Caution around convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Cornices

Large fragile cornices could become weak during afternoon sunny breaks. Not only are they a hazard in themselves, but also a heavy trigger for slabs on the slope below.

Extra caution needed around cornices with current conditions.>Cornices become weak with daytime heating. >

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Feb 28th, 2016 2:00PM