Avalanche Forecast

Issued: Mar 29th, 2016 9:15AM

The alpine rating is considerable, the treeline rating is moderate, 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

A ridge of high pressure dominates for the rest of the week. Sunny and dry conditions are expected for Wednesday through Friday. Freezing levels are expected to be above 3000m each afternoon, with cooling overnight. Light to moderate outflow winds are expected in the alpine for the forecast period.

Avalanche Summary

No new avalanches were reported on Monday. On Sunday, a skier triggered a size 1.5 persistent slab avalanche on a steep roll on a northeast aspect at 1400m elevation. The slab was typically 40cm thick and released on a layer of surface hoar that was buried on March 23. A ski cut at the top of a steep north facing chute at 1100m elevation triggered a size 2 persistent slab which failed on a crust. A helicopter remotely triggered a size 1.5 wind slab from 150m away on an east aspect. Natural cornice releases were reported to have triggered slabs up to size 3.5 which were stepping down to ground. Point releases were reported up to size 2 and glide cracks up to size 2.5. Explosives also triggered a couple size 2 wind slabs on north aspects around 1500m. All of this activity was reported from north of Stewart. On Wednesday, continued warming and sun exposure may result in natural cornice releases, deep persistent slab releases, and loose sluffing.

Snowpack Summary

10-30cm of recent storm snow has accumulated in sheltered areas at higher elevations. In exposed terrain, southerly winds have formed soft slabs in leeward features. A weak crust/surface hoar layer which was buried last week 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 metre. These layers still have the potential to produce large avalanches, especially with a large trigger such as a cornice fall. Extra caution is required during periods of substantial warming and intense solar radiation, as this is when these layers have the biggest potential to wake up. At treeline and below, spring melt-freeze conditions are already being reported. These conditions are expected to extend well into the alpine this week with the forecast warming and sun.

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

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.

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: 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.

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

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 30th, 2016 2:00PM