Avalanche Forecast

Issued: Nov 25th, 2012 9:05AM

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

Avalanche Canada swerner, Avalanche Canada

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 for the entire period

Weather Forecast

Monday-Tuesday will with clear with sunny skies.  No precipitation is expected, ridgetop winds will be light from the NW. Alpine temperatures will remain near -10 with freezing levels generally sitting near 800 m rising to 1100 m Tuesday. 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

No new information today. However, if the recent load did not produce avalanches, I would keep in mind that human triggering is likely. If you and your friends have been out riding in the backcountry, and have observations to share, please send an email to forecaster@avalanche.ca

Snowpack Summary

The region received 15 to 30 cm of snow in the recent storm. Storm slab and wind slabs instabilities exist; however, with the current cooling dry trend this new snow may start to settle and bond. Wind loaded slopes that haven't produced avalanches already are my main concern for human triggering since two fairly deep persistent weak layers are found on all aspects and in the alpine and at treeline. The surface hoar layer is buried under approx. 60 cm, and the early season November crust is deeper, near the bottom of the snowpack ranging from 80 to 100 cm. The facet-crust layer is less reactive, however we do not have recent information about the sensitivity of the surface hoar layer.  There is still a sharp transition in snow depth from treeline to below treeline making backcountry travel more challenging under the 1300 m range.

Problems

Persistent Slabs

An icon showing Persistent Slabs
Two persistent layers exist through the region. A surface hoar layer buried 40-80cm down, and an early Nov crust buried near the base of the snowpack. The weight of a skier, or sledder hitting the sweet spot could trigger these slabs.
Be aware of the potential for triggering a large avalanche due to the presence of buried surface hoar.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Wind Slabs

An icon showing Wind Slabs
Moderate SW winds have redistributed recent storm snow and has formed touchy wind slabs. Wind slabs exist on open leeward slopes and behind terrain features. It may take several days for them to start bonding with the rest of the snowpack.
Use caution on cross loaded slopes at or above treeline.>If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

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

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