Avalanche Forecast

Issued: Feb 27th, 2016 7:39AM

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

Purcells.

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 1400-1600 m. Ridge winds are moderate from the S-SW. Monday: Cloudy with sunny breaks and a chance of flurries. The freezing level rises to 1000-1200 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 consisted mainly on loose wet sluffs on steep sun-exposed slopes and natural cornice falls to size 2. On Thursday, numerous natural loose avalanches up to size 2.5 were reported from steep sun exposed slopes. Explosives triggered a bunch of cornices up to size 2.5 and a couple natural cornices releases was also reported. Most of these cornices were on north aspects at treeline and in the alpine. Two cornice releases slabs on the slopes below. One was a 35cm thick wind slab on north aspect at 2600m and the other was 60cm thick slab on a north aspect at 2100m. Wind slabs were reported to be reactive to ski cutting in immediate leeward features in the far north of the region.

Snowpack Summary

A dusting of new snow overlies a melt-freeze crust on solar aspects and lower elevation terrain, and might be covering a layer of surface hoar on shady and sheltered slopes at treeline and in the alpine. New wind slabs are expected to form over the weekend with forecast moderate southwest winds in the alpine. The surface hoar and/or crust layer which was buried February 10 is now down 40-70cm and has been responsible for some 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. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on this layer has become unlikely but it still has isolated potential to produce very large avalanches with a heavy trigger. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Problems

Wind Slabs

Thin new 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.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

The likelihood of triggering the weak crust/surface hoar layer down 40-70cm is decreasing with colder temperatures but may still be triggered with heavy triggers like cornice falls or smaller avalanches stepping down.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Cornices

Large fragile cornices could weaken 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.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

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