Avalanche Forecast

Issued: Mar 30th, 2016 8:10AM

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

rbuhler, Avalanche Canada

Northwest Coastal.

A special warning has been issued for the substantial warming and sun this week. Deeply buried weaknesses within the snowpack are expected to wake-up and produce very large avalanches. It is best to avoid avalanche terrain during the heat of the day.

Summary

Confidence

Moderate

Weather Forecast

The ridge is expected to persist until Friday evening. Thursday should be sunny with light alpine wind and freezing levels reaching around 3500m in the afternoon. Increasing cloud cover is expected on Friday but mostly sunny conditions are expected for most of the day with freezing levels above 3000m. Alpine winds are expected to increase on Friday evening as the ridge breaks down. A mix of sun and cloud is currently forecast for Saturday with freezing levels dropping to around 1500m and moderate southwest winds in the alpine. Light scattered flurries are possible on Saturday.

Avalanche Summary

On Tuesday, a skier triggered a size 1.5 wet slab avalanche on a steep roll on an east aspect at 1400m elevation. The slab was 10-30cm thick and slide on a crust. A natural size 3.5 was reported north of Stewart on a north aspect at 2200m. This was 3-4m thick and failed on the ground on a steep glaciated feature. Numerous natural cornice failures and loose wet avalanches were reported up to size 2. No new avalanches were reported on Monday. On Thursday, continued warming , sun exposure, and limited overnight recovery means natural cornice releases, deep persistent slab releases, and loose sluffing are expected to continue. Very large avalanches will remain a serious concern for the next few days.

Snowpack Summary

Moist surface snow is being reported to ridgetop on all aspects with wet surface snow below 1500m. 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. A weak crust/surface hoar layer which was buried over a week ago is down 30-40cm in the north of the region. A widespread crust/facet layer buried in early February and a lingering surface hoar layer from January can now be found down over a meter. These old weak layers still have the potential to produce large avalanches, especially with a large trigger such as a cornice fall. Extra caution is required during this period of substantial warming and intense solar radiation, as this is when these layers have the biggest potential to wake up.

Problems

Deep Persistent Slabs

Deeply buried weak layers which have been dormant recently are expected to wake up this week with the substantial warming and sun exposure. Very large avalanches are expected this week.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >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

Possible - Likely

Expected Size

3 - 6

Cornices

Large lingering cornices are expected to become weak with the substantial warming and sun exposure this week. They can be destructive by themselves, and may also become the trigger for a large slab avalanche on the slope below.

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

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 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 - 3

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