Avalanche Forecast

Issued: Nov 23rd, 2012 8:32AM

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

swerner, Avalanche Canada

South Rockies.

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

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

A Pacific frontal system is moving through the interior regions Friday and extending into Saturday. This will bring strong ridgetop winds, and light-moderate amounts of snow. After the front passes, a weak ridge of high pressure will push into the region bringing dryer, cooler, and clearing conditions that will last through the weekend. Freezing levels will stay in the valley bottom through the period.

Avalanche Summary

Reports of audible large avalanches were heard around the Harvey Pass zone yesterday. Several crowns were spotted on North through East aspects with wide propagation. If you and your friends have been out exploring and riding in the backcountry, and have some observations to share please send us an email to forecaster@avalanche.ca.

Snowpack Summary

Snowpack observations and information are extremely limited, and conditions across the region vary. Building storms slabs and wind slabs likely exist in the alpine and at treeline elevations. An early season (Nov 8) rain crust has been reported to exist around 2000 m and above on NW-NE aspects. A recent field test from the Harvey Pass area shows an ECTN 18 down 85 cm on top of the crust, ECTP22 down 75 cm on last weeks storm interface. In the alpine I suspect 100 + cm of snow, and treeline seeing an average around 90 cm. Below treeline snow levels could be reaching threshold.

Problems

Wind Slabs

Wind slab instabilities exist and may be touchy to rider triggers. Wind slabs can be found on lee slopes and behind terrain features. Storm slab instabilities may still exist on all aspects, and require a couple days to settle out.�

Avoid cross loaded slopes at or above treeline.>Use ridges or ribs to avoid pockets of wind loaded snow.>Be alert to conditions that change with elevation.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

The early Nov. crust is buried down approximately 80 cm of snow near the base of the snowpack. It is a suspect sliding layer that may have caused large avalanches recently. The weight of a skier or sled may be able to trigger this slab.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Ride slopes one at a time and spot for your partners from safe locations.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 5

Valid until: Nov 24th, 2012 2:00PM