Avalanche Forecast

Issued: Mar 30th, 2016 9:30AM

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

rbuhler, Avalanche Canada

South Coast.

A special warning has been issued for the substantial warming and sun this week. Extra caution is required around and below cornices, and on steep sun exposed slopes during the heat of the day. Deep persistent avalanches may also become possible.

Summary

Confidence

Moderate

Weather Forecast

The ridge of high pressure is expected to persist until Saturday morning. Thursday and Friday should be sunny with light alpine wind from the northwest and afternoon freezing levels above 3000m. Increasing cloud cover is expected on Saturday with moderate alpine wind from the southwest and freezing levels dropping below 2000m. Light scattered flurries are possible Saturday afternoon.

Avalanche Summary

On Tuesday, widespread natural loose wet sluffing was reported on solar aspects up to size 2.5 A natural size 2 wind slab avalanche was also reported in large open icefield area caused by down flowing wind. Natural cornice failures up to size 2.5 were also observed. On Monday, skier triggered avalanches up to size 1.5 were reported. The recent storm snow overlying a melt-freeze crust was reactive to triggering in wind affected terrain. Loose sluffing was also reported from steep southerly slopes. On Thursday, continued warming, sun exposure, and limited overnight recovery means natural cornice releases and loose sluffing are expected to continue. As the warm temperatures continue, deep persistent weak layers have the potential to become reactive and produce very large slab avalanches.

Snowpack Summary

A moist snow surface is reported to be widespread to mountaintops except for shaded true north aspects at the highest elevations. Warm overnight temperatures means there was a limited refreeze of the snow surface. A thin crust may have formed in some areas but is expected to quickly break down in the morning. Wind affected surfaces are reported in exposed alpine terrain in response to recently strong northerly winds. Large cornices are lingering and are expected to become very weak with the sustained warming this week. Below the snow surface, there are two layers of concern in the northern half of the region. Professionals are tracking a melt freeze crust down around 40cm and a thick layer of facets down 120cm. As the snowpack continues to heat up this week, these layers have the potential to wake-up and produce very large avalanches.

Problems

Cornices

Large cornices are expected to get weak with warming and sun exposure, and natural cornice releases are possible in the afternoon. They can be destructive by themselves, and may also become the trigger for a slab avalanche on the slope below.

Give cornices a wide berth when traveling on or below ridges. >Extra caution needed around cornices with current conditions. >Cornices become weak with daytime heating, so travel early on exposed slopes. >

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Loose Wet

Loose wet sluffing is expected on sun exposed slopes during the heat of the afternoon. Very high freezing levels may increase the size and run length of natural sluffing.

Be cautious of sluffing in steep terrain.>Start and finish early before the surface crusts melt. >Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Deep Persistent Slabs

There is concern that buried weak layers may wake-up with the warming this week, especially in the northern half of the region. Pros are tracking a crust down 40cm and a facet layer down 120cm. Very large avalanche may be possible in isolated areas.

Be aware of the potential for large, deep avalanches due to the presence of buried weak layers. >Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Cornice releases have the potential to trigger deeply buried weak layers. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 31st, 2016 2:00PM