Avalanche Forecast

Issued: Nov 28th, 2018 5:09PM

The alpine rating is considerable, 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.

With few field observations, uncertainty exists around the buried, weak surface hoar layer. We suspect that the potential for human triggered avalanches remain high. Please post your observations to the Mountain Information Network.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

The weather trend will start to stabilize as a high pressure system sets up through the forecast period. THURSDAY: Mostly cloudy with new snow 5-10 cm/Â alpine temperatures near -7/Â generally light winds from the southeast/ freezing level 900mFRIDAY: Cloudy with a trace of new snow/Â alpine temperatures near -9/Â ridgetop winds light from the southeast/Â freezing levels 1400 mSATURDAY: Mix of sun and cloud/Â alpine temperatures -11/Â ridgetop winds light from the northeast/Â Freezing levels near 800 m

Avalanche Summary

Numerous natural loose dry avalanches up to size 1 from steeper terrain features were reported on Tuesday with less action Wednesday. With little avalanche observations and low confidence of the surface hoar distribution, I suspect that human triggered avalanches remain possible, especially where deeper deposits of storm snow sit above the buried weak layer.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.Â Check outÂ the MIN report here.

Snowpack Summary

The early season snowpack is highly variable in this region. Approximately 20 cm new snow fell in this area during the most recent storm, which may have been blown into wind slabs on exposed northerly and northeasterly slopes. 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 - Likely

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 storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Nov 29th, 2018 2:00PM