Avalanche Forecast

Issued: Mar 16th, 2019 4:38PM

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

jsmith, Avalanche Canada

Purcells.

Warming temperatures have settled the recent storm snow into a cohesive slab sitting on weak facets (sugary snow) that is ripe for human triggers; intense solar radiation will increase the likelihood of natural and human triggered avalanches.

Summary

Confidence

Moderate -

Weather Forecast

SATURDAY NIGHT: Mostly clear / Light, northwesterly winds / Alpine low -4 / Freezing level valley bottom.NOTE: Saturday 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.SUNDAY: Sunny / Light, northerly winds / Alpine high 4 / Freezing level rising to 2100 m.MONDAY: Sunny / Light, northeasterly winds / Alpine high 7 / Freezing level rising to 2600 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 8 / Freezing level rising to 2800 m.

Avalanche Summary

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.On Thursday, several rider triggered persistent slab avalanches up to size 2 were reported on a variety of aspects at treeline elevations.On Wednesday, numerous naturally triggered wind slab avalanches up to size 2.5 and a few human triggered wind slabs up to size 1.5, were reported primarily on easterly aspects at treeline and above.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 2.5

Cornices

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

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Loose Wet

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

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.Reduce exposure to over-head hazards such a large cornices during periods of strong solar radiation.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 1.5

Valid until: Mar 17th, 2019 2:00PM