Avalanche Forecast

Issued: Mar 21st, 2014 9:45AM

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

South Columbia.

The snowpack remains complex due to stubborn buried weak layers. Very large, destructive avalanches are still possible. Conservative route selection remains crucial at this time.

Summary

Confidence

Good

Weather Forecast

A weak frontal system should bring light precipitation to the interior midday Saturday. A ridge of high pressure builds in its wake on Sunday and should persist through Monday. The next system is expected for Tuesday.Saturday: Light precipitation 3-5mm, freezing level am: surface pm: 800m, ridgetop wind light SW-WSunday: Mostly sunny, dry conditions, freezing level am: 400m pm: 1200m, ridgetop wind light W-NWMonday: A mix of sun and cloud, dry conditions, freezing level am: 500m pm: 1500m, ridgetop wind light SW-W

Avalanche Summary

Reports from Thursday include numerous natural and skier triggered avalanches up to size 2.5. These occurred on all aspects and elevation bands, and typically released down 30-40cm. One avalanche stepped down to the early-March layer. In the N. Columbia region, one avalanche stepped down to the early-February layer.Generally, we are 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

30-60 cm of recent storm snow sits on the mid-March interface, which is commonly described as a sun crust/surface hoar sandwich. Recent snowpack tests show variable results on this weakness, with mostly hard shears where the storm snow overlies surface hoar. Periods of gusty SW-NW winds have redistributed some of the new snow forming soft wind slabs in exposed lee terrain.The early March persistent weak layer, which is a crust mixed with facets or surface hoar in places, is now down around 80-120 cm. This layer has been most reactive on southerly aspects. The mid-February crust/facet/surface hoar layer is widespread throughout the region, but the depth varies significantly. It still producing sudden "pops or drops" results in snowpack tests where it is less than 150 cm deep. The biggest concern with this interface is being able to trigger it where it is less deep and having it propagate into thick snowpack areas producing very deep and large avalanches. Cornices are also large and fragile at this time and could pop off during sunny breaks.

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

The early February 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 thin areas that may propogate to deeper instabilites.>Be aware of the potential for large, deep avalanches due to the presence of deeply buried weak layers.>Avoid rock outcroppings, large convexities and anywhere the snowpack is thin and/or variable.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Mar 22nd, 2014 2:00PM