Avalanche Forecast

Issued: Nov 25th, 2012 9:00AM

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

swerner, Avalanche Canada

South Columbia.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the Forecasters Blog for further details on interpreting early season bulletins.

Summary

Confidence

Poor - Due to limited field observations on Wednesday

Weather Forecast

Monday-Tuesday will see patchy valley cloud in the mornings with clear, sunny skies in the afternoon. No precipitation is expected, ridgetop winds will be light from the NW. Alpine temperatures will remain near -5 with freezing levels generally sitting near 900-1200 m. Wednesday should start to see a change as the next system sets up. Timing and intensity of Wednesdays system is uncertain. Freezing levels may climb to 1500 m, and winds will switch out of the South.

Avalanche Summary

On Friday a widespread cycle occurred during the recent storm. Natural avalanches up to 2.5 ran on all aspects with good propagation. Slab depths were 40-60 cm deep and mainly confined to N- NE aspects on alpine slopes. Natural activity is likely over now, but I'm still concerned that human triggers will be a factor over the next couple days.Recently, several loose size 1.5-2.0 natural avalanches have occurred in the northern part of the region.

Snowpack Summary

Recent storm snow accumulations across the region vary from 25-50 cm. Storm slabs and wind slabs have formed and add an additional load to the snowpack. During this dry, cool period the new snow should start to settle out, and bond to the upper pack but loose dry sluffing may occur from steeper, larger terrain features.Some persistent weak layers linger deeper in the snowpack. A buried surface hoar layer has been reported. Not sure how wide spread it is across the region, but the average depth is down 60 cm and found in specific, sheltered locations. Below this (down 80-110 cm) sits the early November crust. Tests have been showing easy to moderate SP (sudden planar) pops on weak facetted crystals at this crust interface, or within the crust sandwich.The snowpack depth in the alpine ranges from 130-225 cm. Treeline near 150 cm. A sharp transition is still seen below treeline, where the snowpack peters out around 1300 m.

Problems

Storm Slabs

Recent storm snow has built storm slabs. Mod-strong SW winds have developed wind slabs in the alpine on N-E aspects. If the solar influence is high today, watch steeper solar aspects as the avalanche danger may increase.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Use ridges, ribs or knolls to avoid pockets of wind loaded snow.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

A surface hoar layer sits on avg. down 60 cm. This may react to human triggers. A variable facetted crust exist lower in the snowpack at ALP and in the TL. Easy to moderate SP (sudden planar) pops on weak facetted crystals at this crust interface.

Be aware of the potential for large avalanches due to deeply buried weak layers.>It may be low probability to trigger this slab, but result in high consequences.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Nov 26th, 2012 2:00PM