Avalanche Forecast

Issued: Jan 15th, 2014 9:19AM

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

jlammers, Avalanche Canada

Purcells.

Warm temperatures and sunny skies forecast for the next few days will have a significant weakening effect on the snowpack. If solar radiation is particularly strong, the avalanche danger could rise to HIGH.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

Generally clear skies are expected for the forecast period as a ridge of high pressure becomes established over much of the province. Winds are forecast to be light to moderate from the northwest becoming southwesterly on Saturday. Daytime alpine temperatures are expected to hover between 0.0 and +5.0.

Avalanche Summary

Natural and explosive-triggered avalanches to size 3.5 were observed in the region on Tuesday. Many of the avalanches started within the recent storm snow, and then stepped down to basal facets at ground level. In 2 cases, natural cornice fall was the trigger.I would add loose wet avalanches to the mix with forecast warming. Warming may also promote ongoing persistent slab activity.

Snowpack Summary

Recent snowfall amounts were highly variable throughout the forecast area, with the western parts of the range getting as much as 90cm in the past week. The new snow sits on a variety of snow surfaces including older wind slab, a soft layer of facetted snow and/or surface hoar buried in early January.In the mid pack you may find a surface hoar layer buried in mid December. Further down you may also find the December facet/crust combo. Both interfaces give variable results in snowpack tests, but professional operators are treating them with caution.A big concern throughout the region is a layer of weak sugary depth hoar at the base of the snowpack. These crystals lie above a crust which formed in October. Several large avalanches in the past few weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, and an alarming tendency for seemingly disconnected slopes to propagate over a wide area and produce large avalanches.

Problems

Persistent Slabs

A number of persistent weakness exist in the snowpack, the most notable being weak, sugary facet crystals at ground level. Forecast warming may promote ongoing avalanche activity at this interface with the potential for large, destructive avalanches.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Loose Wet

Forecast warming will likely produce loose wet avalanches in steep, sun-exposed terrain. A loose wet avalanche in motion may also "step down" triggering deep and destructive slab avalanches.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Avoid exposure to solar aspects overhead, large avalanches may reach the end of run out zones.>Sluffs may trigger deeper instabilities.>

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Storm Slabs

Although storm slabs may be gaining strength, they may be particularly reactive in steep, wind-affected terrain, or in areas where they overlie buried surface hoar.

Be cautious as you transition into wind affected terrain.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Jan 16th, 2014 2:00PM