Avalanche Forecast

Issued: Mar 17th, 2017 4:45PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs, Deep Persistent Slabs and Cornices.

cgarritty, Avalanche Canada

Lizard-Flathead.

Saturday's weather puts all the ingredients in place for a natural avalanche cycle to generate large, destructive avalanches. Extreme caution is required for any travel in avalanche terrain.

Summary

Confidence

Moderate -

Weather Forecast

Friday night: Wet flurries bringing approximately 10 cm of new snow to higher elevations. Rain below about 1700 metres. Strong to extreme southwest winds. Saturday: Periods of snow and rain bringing 15-30cm of new snow to higher elevations. Rain below about 1800 metres. Strong to extreme southwest winds. Freezing level to 2200 metres with alpine temperatures of 0 to +1. Sunday: Sunny with cloudy periods. Moderate west winds. Freezing level to 1500 metres with alpine temperatures around -6. Monday: A mix of sun and cloud Light southeast winds. Freezing level to 1700 metres with alpine temperatures around -5.

Avalanche Summary

Reports from Thursday show a continuation of the recent avalanche cycle, with storm slabs releasing naturally to Size 2 and explosives controlled deep persistent slabs to Size 3. North to northeast aspects have been the most active. Most crown fractures have measured about one metre but one impressive storm slab featured a three metre fracture depth.Reports from Wednesday showed widespread natural avalanches up to Size 3.0. Most of these were reported to be loose wet avalanches gouging and entraining mass as they travelled down the path. The heightened avalanche activity shown by the above reports should be expected to persist on Saturday.

Snowpack Summary

5-10 cm of new snow fell over Thursday night. Below it, recent heavy rain to mountain tops has soaked the upper snowpack and caused rapid settlement of our recent storm snow. Below freezing temperatures since the rain event have refrozen the wet snow into a crust, which has been reported to be supportive above about 1700 metres. The existence of this crust may not have much of a stabilizing effect on the snowpack, especially as freezing levels rise again on Friday through Saturday. Isolated basal facets still exist in shallow snowpack areas and can produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls, sustained warming, or storm slab avalanches.

Problems

Storm Slabs

A potentially heavy snowfall will combine with intense winds to form touchy new storm slabs at high elevations on Saturday. Rain may fall as high as 1800 metres and promote loose wet avalanches. Both problems have the potential to trigger deep slabs.

If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

2 - 3

Deep Persistent Slabs

The lack of an overnight refreeze will make the impact of Saturday's 2200m freezing levels even stronger. Warming aside, new snow, wind, and rain are set to provide ample natural triggers for deep persistent slabs.

Avoid overhead exposure during heavy loading from new snow, wind, and rain.Wind slabs, cornices, or loose wet avalanches may trigger deep layers and result in large avalanchesRecognize and avoid avalanche runout zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Cornices

Cornices are huge and are ripe for releasing after sustained warm temperatures. Cornice falls are an excellent trigger for large persistent slab avalanches.

Maintain constant awareness of overhead hazards.Even small cornice falls may trigger larger avalanches.Avoid exposure to overhead hazard from cornices.

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Mar 18th, 2017 2:00PM