Avalanche Forecast

Issued: Apr 20th, 2014 8:35AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs, Loose Wet and Cornices.

rbuhler, Avalanche Canada

Sea To Sky.

Avalanche danger can rise quickly with afternoon warming and solar radiation. Be aware of changing conditions and overhead hazards.For more insight into spring danger ratings, check out this Blog Post.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Light precipitation is expected to continue for Monday and Tuesday. A weak ridge of high pressure should bring at least partially sunny conditions for Wednesday. There is some model uncertainty and a possibility that the ridge could build over the south coast on Tuesday.Monday: Precipitation 2-4mm, freezing level am: 1200m pm: 1700m, ridgetop wind: light S-SWMon. Night/Tuesday: Light precipitation 3-6mm, freezing level am: 1200m pm: 1500m, ridgetop wind: light SWWednesday: A mix of sun and cloud, convective flurries possible, freezing level am: 1000m pm: 1600m, ridgetop wind: light SW

Avalanche Summary

On Saturday, explosive control released a cornice which triggered a size 2.5 slab that released to ground. A natural size 1 cornice and isolated size 1 soft slabs from leeward features were also reported.On Friday, several storm slab avalanches up to size 2 were reported. These were triggered both by skiers and explosives and released down 10-50cm. Natural soft slab avalanches up to size 2.5 were also reported in the region releasing in the storm down 20-35cm with good slab propagation. Natural sluffing from steep features to size 1.5 was also reported.

Snowpack Summary

A highly variable spring snowpack exists across the region and conditions can change rapidly throughout the day. At lower elevations below-treeline, the snowpack is isothermal and melting rapidly. At mid elevations, between roughly 1500 and 2000m (and higher on sunny slopes), the snowpack is undergoing daily melt-freeze cycles. In the mornings, a refrozen surface generally means good stability. In the afternoon when the surface melts, the stability can deteriorate quickly, especially on sunny slopes. The recent storm has produced dry snow in the alpine resulting in the formation of storm slabs and wind slabs which sit on an old crust. The stability of these slabs has generally been improving but on the first really sunny day, stability is expected to deteriorate rapidly and natural avalanche activity is likely, especially on sunny slopes. Large cornices remain a concern and are expected to become reactive during periods of solar warming. The early-Feb facet/crust layer (down ~2m) and a weak basal layer are both dormant but remain a concern during periods of intense warming, especially in thinner snowpack areas, when large spring avalanches may step down to these layers.

Problems

Wind Slabs

Strong S-SW winds have formed wind slabs in leeward alpine features.

Be cautious as you transition into wind affected terrain.>Use caution in lee areas in the alpine. Recent wind loading have created wind slabs.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 3

Loose Wet

Loose wet activity can be expected from steep features during periods of solar warming or rain. Isolated wet slabs may be possible under the same conditions where the recent storm snow is poorly bonded to the underlying crust.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Cornices

Large cornices may become reactive during periods of sun and warming. Cornice falls have the potential to trigger deep instabilities which could result in large, destructive avalanches.

Give cornices a wide berth when travelling on or below ridges.>Cornices become weak with daytime heating, so travel early on exposed slopes.>

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

Valid until: Apr 21st, 2014 2:00PM