Avalanche Forecast

Issued: Mar 17th, 2019 4:57PM

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

jsmith, Avalanche Canada

Purcells.

Overhead hazards, such as large avalanche paths and cornices will be a major concern over the next few days. Sporadic, very large natural avalanches may run full path to valley bottoms. Avoid all avalanche terrain during periods of rapid warming.

Summary

Confidence

Moderate -

Weather Forecast

SUNDAY NIGHT: Clear / Light, northeasterly winds / Alpine low -2 / Freezing level 1500 m.NOTE: Sunday night is the last night of the forecast period that freezing levels are expected to drop at night. This will significantly increase the impact of day time warming on the snowpack.MONDAY: Sunny / Light, northeasterly winds / Alpine high 4 / Freezing level rising to 2700 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 6 / Freezing level rising to 3000 m.WEDNESDAY: Sunny / Light, southeasterly winds / Alpine high 7 / Freezing level 3000 m.

Avalanche Summary

On Saturday, several naturally triggered, persistent slab avalanches up to size 3 were reported on a variety of aspects in the alpine. Natural avalanche activity and size of avalanches are expected to increase during the next few days.On Friday, a natural size 2.5 and explosive triggered size 3 persistent slab avalanches were reported on north aspects in the alpine. Human triggered persistent slab avalanche activity is expected to increase with the forecast sunshine and rising freezing levels.

Snowpack Summary

15-30 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 a weak layer of surface hoar (weak, feathery crystals) buried in mid-January can be found approximately 50-90 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 in low elevation areas such as steep cutblocks and large open glades.The base of the snowpack is composed of facets (weak, sugary snow) that sit on a crust. Very large avalanches failing on this persistent weak layer will become more likely with the forecast sunshine and rising freezing levels.

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

Expected Size

1.5 - 2.5

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

Possible - 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 exposure to terrain traps where the consequences of a small avalanche could be serious.Avoid steep, sun exposed slopes when the solar radiation is strong.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

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