Avalanche Forecast

Issued: Mar 17th, 2019 4:37PM

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

jsmith, Avalanche Canada

South Columbia.

A widespread natural avalanche cycle is forecast for Monday. Travel in avalanche terrain is NOT recommended.

Summary

Confidence

Moderate -

Weather Forecast

NOTE: Freezing levels are forecast to remain elevated overnight throughout the forecast period. This will significantly increase the impact of day time warming on the snowpack.SUNDAY NIGHT: Clear / Light, northeasterly winds / Alpine low 0 / Freezing level 2500 m.MONDAY: Sunny / Light, northeasterly winds / Alpine high 5 / Freezing level rising to 3000 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 7 / Freezing level 3000 m.WEDNESDAY: Sunny / Light, southeasterly winds / Alpine high 8 / Freezing level 3000 m.

Avalanche Summary

On Saturday, numerous naturally triggered, persistent slab avalanches were reported on all aspects at treeline and above. Additionally, a snowcat triggered a size 1.5 avalanche on a steep road bank which reportedly failed on the surface hoar layer buried in mid-January. This is notable because it may indicate that this weak layer that has been dormant for many weeks is being brought back to life by the rapid warming of the snowpack.On Friday, numerous natural loose wet and persistent slab avalanches up to size 2 were reported on solar aspects at all elevations. A skier triggered, persistent slab, size 2 avalanche was reported on a south aspect at 2000 m. Human triggered persistent slab avalanche activity is expected to increase with the forecast sunshine and rising freezing levels.

Snowpack Summary

There is 30-60 cm. of recent storm snow is sitting on a pile of facets (sugary snow), as well as a crust on sun exposed slopes. The recent storm snow has settled into a cohesive slab and is ripe for human triggering. This persistent slab is currently our primary concern.At lower elevations below treeline, a weak layer of surface hoar (weak, feathery crystals) buried in mid-January can be found approximately 60-120 cm. deep and may be combined with a crust on south facing slopes. This layer has recently been unreactive, however, the forecast warming event may awaken this layer, resulting in large, destructive avalanches. Steep cutblocks and large open glades at lower elevations are the most likely places to trigger this layer.The lower snowpack is generally considered to be strong in most areas; except for rocky areas in the alpine with a shallow snowpack where multiple days of intense sunshine and warming could trigger sporadic very large avalanches running to valley bottoms.

Problems

Persistent Slabs

Warming temperatures have settled the recent storm snow into a cohesive slab sitting on weak facets (sugary snow) that is ripe for human triggers; especially at treeline and above.

Avoid convex slopes on rocky terrain with a variable snow depth.Use extra caution on solar aspects where the new snow is sitting on a crust.Avoid steep terrain where the snow feels moist or slabby.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1.5 - 3

Cornices

Sunshine and rising freezing levels will elevate the potential for cornice failures resulting in large avalanches.

Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.Cornice failures have the potential to trigger large avalanches on deeply buried weak layers.Avoid exposure to cornices and sun exposed slopes when the solar radiation is strong.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 3

Loose Wet

Pin-wheeling snow below cliffs is a common sign that loose wet avalanches are becoming more likely.

Reduce exposure to over-head hazards such a large cornices during periods of strong solar radiation.Avoid steep, sun exposed slopes when the solar radiation is strong.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Valid until: Mar 18th, 2019 2:00PM