Avalanche Forecast

Issued: Nov 30th, 2018 4:02PM

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

swerner, Avalanche Canada

Purcells.

Wind slabs may be more reactive to human triggers where they sit above a buried weak layer. The alpine has its own uncertainties. Check out the New forecaster blog HERE.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

Mostly cloudy skies, cooling temperatures and dryer conditions into the weekend. SATURDAY: Mostly cloudy with a trace of new snow/ alpine temperatures near -7/ generally light winds from the northeast/ freezing level 900 mSUNDAY: Mix of sun and cloud/ alpine temperatures near -12/ ridgetop winds light from the northeast/ freezing levels 700 mMONDAY: Cloudy with sunny periods/ alpine temperatures -11/ ridgetop winds light from the northeast/ freezing levels valley bottom

Avalanche Summary

No recent reports on Friday. On Thursday, reports indicated that the weight of a skier could trigger small, isolated pockets of wind slab up to size 1 from steeper terrain features. With little for avalanche observations and low confidence of the buried surface hoar distribution, I suspect that human triggered avalanches remain possible, especially where deeper deposits of storm snow or wind slabs sit above a buried weak layer. I also suggest keeping the basal crust on your radar. Steeper, thin-thick rocky alpine features are more suspect.Last Saturday, a large human triggered avalanche was reported in the South Columbia forecast region. The size 3 avalanche occurred on a steep, north aspect in the alpine and failed to ground, likely on the October crust. This avalanche is notable for the Purcells where we have a similar, but shallower snowpack than in the South Columbia, resulting in a higher possibility of impacting a weak layer near the ground. Check out the MIN report here.

Snowpack Summary

The early season snowpack is highly variable in this region. Approximately 20 cm of recent snow fell earlier this week which may have been blown into wind slabs on exposed northerly and northeasterly slopes. Expect loose dry, unconsolidated snow sluffing from steeper, rocky terrain features. In most places, there are two layers of feathery surface hoar being reported, one around 20 cm below the surface and one down 35 cm. One or both of these may be associated with a crust on south aspects. The most likely places to trigger one of these layers is in deeper snow areas in shady spots on smooth slopes. A prominent feature of the snowpack is a combination of a crust and underlying sugary, faceted snow found near the base of the snowpack. It may still be possible to release an avalanche on smooth slopes in the alpine.

Problems

Wind Slabs

Recent new snow and wind will have set up wind slab problems that are most likely found on steep, smooth, north to east facing slopes. They could be more reactive where they sit above a weak, feathery surface hoar layer.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Caution in lee and cross-loaded terrain near ridge crests.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

A nasty combination of crust and sugary, faceted snow exists at the base of the snowpack in the alpine. This layer could produce avalanches on steep, smooth slopes in the alpine.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Large alpine slopes with a thin-thick, rocky snowpack are suspect to triggering.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Dec 1st, 2018 2:00PM