Avalanche Forecast

Issued: Mar 18th, 2017 3:56PM

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

cgarritty, Avalanche Canada

Lizard-Flathead.

Temperatures may cool, but the snowpack is still warm and the sun will be out in full force on Sunday. There is no reason to expect a rapid drop in avalanche danger.

Summary

Confidence

Moderate -

Weather Forecast

Sunday: Sunny. Moderate to strong west winds. Freezing level to 1400 metres with alpine temperatures around -7. Monday: A mix of sun and cloud. Light east winds. Freezing level to 1500 metres with alpine temperatures around -6. Tuesday: Cloudy with isolated flurries and a trace of new snow. Light south winds. Freezing level to 2000 metres with alpine temperatures around 0.

Avalanche Summary

Reports from Friday show a continuation of the recent and ongoing avalanche cycle, with several observations showing explosives triggered persistent slabs (and one storm slab) running from Size 2.5-3. Crown fractures generally ranged from 100-200 cm. On Thursday, storm slabs were observed releasing naturally to Size 2, with explosives control yielding deep persistent slabs to Size 3. Most crown fractures measured about one metre but one impressive storm slab featured a three metre fracture depth. North to northeast aspects were the main performers over both days.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. Looking forward, recently formed storm slabs in the alpine will likely be reactive to human triggering on Sunday. The heightened avalanche activity shown by the above reports should gradually decrease as cooling temperatures begin to penetrate the snowpack.

Snowpack Summary

Stormy weather on Saturday has been forming storm slabs at high alpine elevations while rain continues to saturate the snowpack at treeline and below. Below the new snow accumulations, recent heavy rain to mountain tops 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. This crust will deteriorate at all elevations where rain is occurring before gradually reforming as temperatures cool again on Saturday night. 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 and storm slab avalanches.

Problems

Deep Persistent Slabs

Be careful not to overestimate the stabilizing effect of cooling temperatures on Sunday. Rain has saturated the snowpack with warmth and deep persistent slabs still have the potential to release naturally or with a sufficient trigger on Sunday.

Recognize and avoid avalanche runout zones.Storm slabs, cornices, or a rider's weight may trigger deep layers and result in large avalanches.Avoid exposure to overhead hazards when solar radiation is strong.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Storm Slabs

All the rain that soaked lower elevations fell as snow above about 2000 metres. Expect touchy storm slabs that thicken with elevation in the alpine and be aware that they are an overhead hazard to lower elevations, especially when the sun comes out.

Be alert to conditions that change with elevation.If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Minimize exposure to sun exposed slopes when solar radiation is strong.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

2 - 3

Cornices

Recent warm, stormy weather has seen cornices become huge and ripe for releasing as the sun hits them on Sunday. Cornice falls are an excellent trigger for large persistent slab avalanches.

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

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Mar 19th, 2017 2:00PM