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Archived

Avalanche Forecast

Nov 26th, 2012–Nov 27th, 2012
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Purcells.

This bulletin is based on a very small amount of stale data. Local variations in conditions are likely to exist. Check out the Forecasters Blog for further details on interpreting early season bulletins.

Confidence

Poor - Due to limited field observations

Weather Forecast

Tuesday should produce fairly benign weather.  Hi cloud with the occasional sunny break is the most likely scenario.  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 [email protected]

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 challenging below 1300 m.

Avalanche Problems

Persistent Slabs

Two problem layers exist: A surface hoar layer 40 - 80 cm below the snow surface and the early Nov. crust near the ground.  It's possible for a rider to trigger these weak layers, especially in areas where the snowpack is thin and/or rocky.
Avoid convexities or areas with a thin or variable snowpack.>Avoid thin, rocky or sparsely-treed slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 5

Wind Slabs

Moderate SW winds associated with the recent storm formed windslabs that are likely diminishing in rider "triggerability."  Be wary of wind exposed terrain at and above treeline. 
Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 4