Avalanche Forecast

Issued: Mar 19th, 2017 4:25PM

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

cgarritty, Avalanche Canada

Lizard-Flathead.

We're in a period of uncertainty as cooling temperatures gradually stabilize the snowpack. Continue avoiding large avalanche paths and overhead hazards.

Summary

Confidence

Moderate -

Weather Forecast

Monday: Cloudy with sunny periods early in the day. Light east winds. Freezing level to 1500 metres with alpine temperatures around -6. Tuesday: Cloudy with scattered flurries bringing approximately 5 cm of new snow, mainly in the evening. Light southeast winds. Freezing level to 2000 metres with alpine temperatures around 0. Wednesday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Strong southwest winds. Freezing level to 2000 metres with alpine temperatures around 0.

Avalanche Summary

Reports from Saturday included observations of one naturally triggered Size 3 deep persistent slab as well as numerous natural storm slab releases occurring on northeast to northwest aspects just west of Fernie. Reports from Friday showed 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.Looking forward, recently formed storm slabs and cornices in the high alpine will likely remain reactive to natural and human triggering on Monday, especially while the sun is out. The heightened avalanche activity shown by the above reports is expected to gradually decrease, but the scale and extent of this activity demands that backcountry users take caution with that assumption.

Snowpack Summary

Stormy weather on Saturday formed fresh storm slabs at high alpine elevations while rain once again saturated the snowpack at lower alpine elevations and below. Lower temperatures have since formed a roughly 10 cm thick crust at the rain soaked surface, which will tend to break down with daytime warming at lower elevations and on solar aspects. Isolated basal facets still exist in shallow snowpack areas and still carry the potential to produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls and storm slab avalanches, which may trigger naturally with daytime warming.

Problems

Deep Persistent Slabs

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

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Storm Slabs

All the rain that soaked lower elevations fell as snow above about 2200 metres. Expect reactive 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

Minimize exposure to sun exposed slopes when solar radiation is strong.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.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Recent warm, stormy weather has seen cornices become huge and they are ripe for releasing when the sun hits them on Monday. 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

Expected Size

1 - 3

Valid until: Mar 20th, 2017 2:00PM