Avalanche Forecast

Issued: Mar 3rd, 2016 7:34AM

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

pmarshall, Avalanche Canada

Purcells.

Storm slabs are highly reactive to human-triggering and conservative terrain selection remains critical for the next few days. Extra caution is required on south-facing slopes in the afternoon if the sun pokes out.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

FRIDAY: A mix of sun and cloud in the morning with light precipitation starting late in the day. Freezing levels reach 1800-2000 m with moderate to strong southwesterly ridgetop winds. SATURDAY: Cloudy with flurries bringing another 3-5cm, followed by sunny breaks. Freezing levels steady around 1800-2000 m and moderate to strong southwesterly ridgetop winds. SUNDAY: A mixed bag sun, cloud, and flurries. The freezing level is around 1800 m and winds ease to light.

Avalanche Summary

Reports from Tuesday and Wednesday include a few explosives and rider triggered storm slab avalanches up to Size 2. Wind and storm slabs should increase in size and likelihood throughout the week with continued light snow and moderate ridge winds. Late last week there were a couple reports of failing cornices triggering persistent slabs up to 60 cm deep on slopes below.

Snowpack Summary

15-30 cm of recent storm snow is bonding poorly to a melt-freeze crust on previously sun-exposed slopes and lower elevation terrain, and/or a layer of surface hoar on shady and sheltered slopes at treeline elevations. Thicker and touchier fresh wind slabs are lurking in exposed lee and cross-loaded terrain. The surface hoar and/or crust layer buried in mid-February is now down 40-70cm. This layer was less reactive over the weekend with cooler temperatures. Large weak cornices remain concerning and have recently triggered persistent slabs on slopes below. 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

Storm Slabs

Fresh storm slabs are primed for human triggering. Particularly touchy wind slabs are lurking below ridge crests, behind terrain features and in cross loaded gullies.

Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Heavier triggers such as cornice falls, groups of people, or smaller avalanches stepping down, or lighter triggers (such as a person) in the wrong spot may be enough load to trigger a crust and/or surface hoar layer down around a 60cm.

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: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Cornices

Warm temperatures, strong winds, and possible sunny breaks are all factors that could weaken large droopy cornices.

Extra caution needed around cornices with current conditions.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

Valid until: Mar 4th, 2016 2:00PM