Avalanche Forecast

Issued: Nov 28th, 2014 8:44AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Loose Dry.

pgoddard, Avalanche Canada

South Rockies.

A Special Public Avalanche Warning is in effect. An intense burst of snow is forecast overnight Friday which may cause a spike in avalanche danger.

Summary

Confidence

Poor - Forecast snowfall amounts are uncertain

Weather Forecast

Very cold arctic air is heading southwards. At the boundary between this cold air and the current warm, moist air, an intense burst of snowfall snowfall is anticipated. Friday night: 20-40 mm precipitation, falling as snow (this could make deep dry snow). Temperatures plummeting. Strong SW winds easing by morning.Saturday: Light snow may continue through the day. Becoming cold and clear by the end of the day. Light winds.Sunday/Monday: Very cold and dry. Light winds.

Avalanche Summary

Explosives triggered two very large (size 2.5 and 3.5) slabs in the south of the region on Thursday around treeline. These failed on a weak layer of facets buried about a week ago. In the north of the region, numerous shallow size 1.5 slabs failed below treeline. Over in the neighboring Lizard/Flathead region, natural and human-triggered avalanches to size 2 have been reported this week. These either failed on basal facets or at the interface below the recent storm snow.

Snowpack Summary

As we begin our forecasting season, we are working with very limited field data. If you have been out in the mountains, we'd love to hear from you. Please email us at forecaster@avalanche.ca.The weather over the past month has created a snowpack full of problems! A weak layer (of facets over a crust) which formed during November's dry spell is now buried a metre or so down. Now it is overloaded with wind-deposited or just plain deep storm snow and we have started to see some very large avalanches in the south of the region. In the upper snowpack, changes in wind and temperature have led to storm slab development. In rain-soaked zones below treeline, the snowpack has been very weak while wet, but should lock up once the deep freeze hits. Add an incoming burst of heavy snow to low levels, and we are likely to see natural avalanches spilling down steep headwalls, with the chance of triggering one of these deeper weaknesses to create a very large avalanche. A good weekend to be cautious while the snowpack has a chance to settle down.

Problems

Persistent Slabs

A touchy weak layer is now buried a metre or so down in the snowpack. It may be reactive to the weight of new snow, wind-loading or the additional weight of a skier or sledder.

Choose regroup spots that are out of avalanche terrain.>Avoid freshly wind loaded features.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 6

Loose Dry

If the weather forecast holds true, expect loose dry and storm slabs to spill down steep headwalls and run in any steep terrain. There is a chance a surface avalanche could trigger something deeper.

Be cautious of sluffing in steep terrain.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Valid until: Nov 29th, 2014 2:00PM