Avalanche Forecast

Issued: Nov 23rd, 2011 8:49AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Persistent Slabs, Wind Slabs and Storm Slabs.

User, Avalanche Canada

Sea To Sky.

Avalanche danger is expected to increase as another intense storm hits the coast.

Summary

Confidence

Poor - Due to limited field observationsfor the entire period

Weather Forecast

Thursday: Snow starting mid-morning and increasing throughout the day with 10-20cm possible by late afternoon. Freezing levels around 900m and strong to extreme southeasterly winds shifting to westerlies and easing off in the evening.Friday: Mostly cloudy with flurries bringing 3-5cm. Freezing levels around 500m, and strong northwesterly winds becoming westerlies late in the day.Saturday: A warm intense Pacific frontal system brings heavy precipitation, extreme winds, and freezing levels possibly into alpine elevations.

Avalanche Summary

Recent reports confirm a widespread destructive natural avalanche cycle during the intense storm overnight Monday. More recent human-triggered whumpfing and large remote avalanches were reported to be associated with the mid-pack crust/facet complex at upper treeline and lower alpine elevations.

Snowpack Summary

Newly formed surface hoar is now buried by 50-70cm of recent storm snow. A persistent weakness of facets, with an associated crust at upper treeline elevations, can be found down 70-150cm. This weakness seems to be particularly touchy between 1800 and 2000m where it is very sensitive to human triggers and has a high propensity to propagate fractures. Buried surface hoar has also been spotted just below this crust, and sitting on top in some locations. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.

Problems

Persistent Slabs

Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m. Potential for remote triggering means that even low-angle terrain may not be safe if there is exposure from above.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Wind Slabs

Near ridgecrests and terrain breaks, and in cross-loaded gullies. Wind slab avalanches can be especially large and destructive.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Storm Slabs

Any open slope with enough snow to smooth out ground roughness. Fluctuating freezing levels created a weak 'upside-down' storm snow structure.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Nov 24th, 2011 8:00AM