Avalanche Forecast

Issued: Mar 20th, 2014 9:44AM

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 Deep Persistent Slabs.

rbuhler, Avalanche Canada

Cariboos.

Expect to see sunny breaks over the next few days. Brief periods of solar radiation could be enough to trigger stubborn persistent slabs or cause cornice failures. Conservative route selection remains crucial at this time.

Summary

Confidence

Fair

Weather Forecast

A cool and unstable NW flow should bring light scattered flurries to the region on Friday. A ridge of high pressure builds on Saturday before a weak upper trough crosses the region Saturday night into Sunday morning.Friday: Cloudy with sunny breaks, scattered flurries 1-3cm, freezing level am: surface, pm: 500m, ridgetop wind: light NW-NSaturday: A mix of sun and cloud, mainly dry, freezing level am: surface, pm: 500m, ridgetop wind: light variableSaturday Night: Flurries 1-4cm, freezing level surface, ridgetop wind: light variableSunday: Cloudy with sunny breaks, mainly dry, freezing level pm: 800m, ridgetop wind: light W-NW

Avalanche Summary

On Wednesday, we received reports sluffing from steep terrain features.Â Also reported were four natural size 2 storm slab avalanches at treeline.Â These released down 30-40cm.We continue to see large natural avalanches stepping down to the deeply buried persistent weak layers. On Tuesday there was one report of a size 2.5 remotely triggered avalanche where a group of skiers felt a massive whumpf at the top of a slope and realized that they triggered an avalanche on an adjacent slope almost 500m away. We're still seeing relatively small inputs, like periods of strong winds or brief sunny breaks, trigger deeper persistent slab avalanches. Many of these events have occurred on southerly aspects from slopes in the alpine or at treeline. Extra caution is advised when the sun is out.

Snowpack Summary

Around 30-40 cm of recent storm snow has fallen in the past few days. There may be a variety of layers within the storm snow from thin sun crusts, to graupel balls, and maybe even recently buried surface hoar from brief clearings overnight. Also, expect fresh wind slabs in exposed lee and cross-loaded terrain. This new snow now sits on a surface hoar and/or sun crust layer. Some recent snowpack tests give moderate "pops or drops" shears on the interface between the recent storm snow and previous surface. A couple other notable persistent weaknesses remain a concern in the mid-snowpack. The surface hoar/sun crust combo buried in early March is now down around 60-80 cm. The early-February surface hoar/facet/crust combo is down 90-150cm and widespread throughout the region. Surface avalanches in motion and cornice fall have the potential to initiate an avalanche on this deeply buried weak layer. The mid and lower snowpack remains weak and facetted in areas with a relatively shallow snowpack.

Problems

Storm Slabs

Weaknesses exist within or under the recent storm snow and could be triggered by the weight of a rider, particularly in steep wind-loaded terrain.

Be cautious as you transition into wind affected terrain.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

The early March sun crust/ surface hoar combo should not be underestimated. While there's a lot of uncertainty and complexity surrounding this layer, it's important to note that human triggering is most likely at treeline.

Minimize exposure to sun exposed slopes when the solar radiation is strong.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

The early February Persistent Weak Layer is still active and has produced some stunning avalanches recently. Very large avalanches may result from a surface avalanche in motion, a cornice fall or a rider finding the sweet spot.

Be aware of the potential for large, deep avalanches due to the presence of deeply buried weak layers.>Avoid rock out croppings, large convexities and anywhere the snowpack is thin and/or variable.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 21st, 2014 2:00PM