Avalanche Forecast

Issued: Mar 22nd, 2014 9:39AM

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.

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

Light flurries Sunday morning are expected to taper off early in the day. A weak ridge of high pressure will build Sunday night and should persist for most of Monday. Some weak disturbance may bring light flurries for Monday night but Tuesday is expected to be mainly dry. The next organized system is expected Tuesday night or Wednesday morning. Freezing levels during the forecast period are expected to be higher in the southern part of the region.Sunday: Mostly cloudy, flurries 0-2cm, freezing level am: surface pm: 800-1200m, ridgetop wind: light NWMonday: Mostly sunny, freezing level am: surface pm: 700-1000m, ridgetop wind: light variableMon. Night/Tuesday: Flurries overnight 3-6cm, freezing level am: 600m pm: 1800m, ridgetop wind: light SW

Avalanche Summary

Reports from Friday include natural storm slab activity up to size 2 on south facing slopes triggered during the afternoon sun.Â Several human-triggered and explosive-triggered storm slabs up to size 2 were also reported.Â These avalanches were typically releasing 15-30cm deep within the storm snow. In the North Columbia region, several avalanches were stepping down to deeper layers.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

Recent storm snow has settled into a 40-60cm slab that sits on the mid-March interface, which is commonly described as a sun crust/surface hoar sandwich. Recent snowpack tests suggest that the reactivity of this layer is becoming more isolated but many areas still have the potential for human-triggering.Â 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. Also, expect some loose wet activity on solar aspects when the sun is out.

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 - 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.

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 weak layer is still active and has produced some stunning avalanches recently. Very large avalanches may result from smaller avalanches stepping down, a cornice fall, or a rider finding the sweet spot.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Mar 23rd, 2014 2:00PM