Avalanche Forecast

Issued: Jan 14th, 2014 9:47AM

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

slemieux, Avalanche Canada

Sea To Sky.

We're dealing with an unusual snowpack right now on the Sea to Sky. Check out the recent Forecasters Blog post for a more detailed discussion

Summary

Confidence

Good

Weather Forecast

Tonight and Wednesday: An inversion will bring fog patches over the low lands and clear conditions up high. Later, a trace to light precipitation is expected with the passage of an unstable airmass with moderate to strong winds from the W shifting from the NW. Freezing levels should lower back to 1300 m. overnight and rise back up again tomorrow to 2000 m. Expect a bit of sun over the region during the day. Thursday: A ridge of high pressure is well in place. Sunny skies and continuing rising freezing levels starting at 2000 m until 3000 m on Friday. Light winds from the W. Friday overlook: Ridge is still dominating the pattern with clear skies and warm temperatures.

Avalanche Summary

Explosive control resulted in avalanche up to size 2.5 some of which ran in the upper storm snow and another in the deep persistent slab on a NE aspect slope. NorthEast of the Sea to Sky region, a significant natural avalanche cycle happened yesterday with the morning heating . Avalanches up to size 3.5 released in the depth hoar basal layer many of which were remotely triggered or naturally triggered. These mostly occurred on N and E facing slopes. Numerous natural avalanche up to size 2.5 are suspected to have released in the late November persistent weak layer.

Snowpack Summary

Past and forecasted moderate to strong winds from the SW-W and NW have formed large windslabs in the alpine and at treeline and scoured windward slopes. I suspect these are bonding rapidly with the present mild temperatures. These windslabs and the old storm snow in sheltered terrain could possibly become more reactive and create moist avalanches as freezing levels rise up tomorrow. This is especially the case for steep slopes getting hit by solar radiation. What is not healing so rapidly is the underlying deep persistent weak layers of facets around crusts and basal facets. At higher elevations, where the snowpack was deeper, the facets likely co-exist with a crust. At lower elevations, or in thin rocky alpine features, more widespread facets exist down near the ground. This makes for a low probability high consequence avalanche scenario that is more commonly associated in the interior of the province. In glaciated terrain open and poorly bridged crevasses are everywhere although now they are hiding under a meter of unsupportive storm snow.

Problems

Deep Persistent Slabs

Recent avalanche activity confirms that weak and reactive layers are lurking deep in the snow pack. Avoid slopes that were shallow and rocky before this last storm. Don't let improving riding conditions tempt you into bigger terrain.

Choose the deepest and strongest snowpack areas on your run.>Be aware of thin areas that may propogate to deeper instabilites.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Wind Slabs

The forecasted temperature rise and solar radiation will weaken the snowpack in the short term especially on steep S facing slopes in the alpine and on all aspects at treeline and below treeline.

Use ridges or ribs to avoid pockets of wind loaded snow.>Enter your line well below ridge crests to avoid wind loaded pillows.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Jan 15th, 2014 2:00PM