Avalanche Forecast

Issued: Mar 17th, 2019 4:27PM

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

North 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, northerly winds / Alpine low -1 / Freezing level 2000 m.MONDAY: Sunny / Light, northerly winds / Alpine high 5 / Freezing level rising to 3000 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 6 / Freezing level 3000 m.WEDNESDAY: Sunny / Light, southeasterly winds / Alpine high 7 / Freezing level 3000 m.

Avalanche Summary

On Saturday, numerous naturally triggered, persistent slab avalanches up to size 3 were reported on all aspects/elevations. Natural avalanche activity and size of avalanches are expected to increase during the next few days.On Friday, several persistent slab avalanches up to size 2.5 were reported on a variety of aspects at treeline and above. The avalanches were failing on facets below the recent storm snow. Human triggered persistent slab avalanche activity is expected to increase with the forecast sunshine and rising freezing levels.On Thursday, a rider triggered size 2.5 persistent slab avalanche was reported on a west aspect at 2000 m. Another size 2, persistent slab avalanche on a southwest aspect at 2300 m. was triggered by a skier from 50 m. away from the slope that avalanched. This suggests that recent storm snow is still very sensitive to human triggers in specific locations.

Snowpack Summary

There is 40-60 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 buried in mid-January can be found approximately 70-120 cm. deep. This layer consists of surface hoar and facets, 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.Avoid steep terrain where the snow feels moist or slabby.Use extra caution on solar aspects where the new snow is sitting on a crust.

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