Avalanche Forecast

Issued: Nov 26th, 2018 4:34PM

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

kdevine, Avalanche Canada

North Columbia.

As the storm continues, keep in mind that the hazard will increase in areas experiencing heavy snowfall, warm temperatures and high winds. Conservative terrain selection and minimizing overhead hazard is recommended.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Forecast snowfall amounts vary greatly throughout the North Columbia, with the highest amounts predicted in the Monashees. MONDAY NIGHT - Snow, 5-15 cm / moderate southerly winds / freezing level 1200 metresTUESDAY - Snow, 10-15 cm / moderate southerly winds / freezing level 1400-1800 metresWEDNESDAY - Cloudy with flurries, up to 5 cm / light to moderate southwest winds / freezing level 1300-1500 metresTHURSDAY - Cloudy with sunny periods and isolated flurries, up to 5 cm / light to moderate southwest winds / freezing level 1200 metres

Avalanche Summary

One natural storm slab avalanche was reported on a northwest aspect at 2700 m on Sunday.Several size 1 rider triggered storm slab avalanches were reported on Monday afternoon.Of note, a size 3 human triggered avalanche that likely ran on the October crust was reported on Saturday, November 24 in the South Columbia region. The avalanche reportedly occurred on a northwest aspect, on a lee feature in the alpine. The full report can be found on the Mountain Information network. Click here to read the report

Snowpack Summary

Ongoing snowfall since Sunday night brings total recent storm snow amounts to anywhere from 30-70 cm by Tuesday morning. As the snow is forecast to continue throughout the day, total accumulations could reach 40-85 cm by Tuesday evening. This new snow sits on top of a weak layer of surface hoar (feathery crystals) and sun crust on steep south facing slopes. The surface hoar is most pronounced at treeline and below, but it may be found in wind sheltered alpine areas.At the base of the snowpack is a crust that formed in late October. There have been no reports of reactivity on this layer in the North Columbia region, however with additional snow, strong winds and rising freezing levels, this layer could come into play during this storm. Storm slab avalanches may have the potential to trigger avalanches on this deeper layer.Total snowpack depths vary greatly with elevation. Recent reports show depths of 120-210cm in the alpine, 80-150 cm at treeline and 10-120 cm below treeline.

Problems

Storm Slabs

30-70 cm sits on a weak layer of surface hoar (feathery crystals) and sun crust. The likelihood of triggering this layer will increase with heavy snowfall, rising freezing levels and wind.

If triggered, the storm slabs may step down to deeper layers resulting in large avalanches.Watch for signs of instability such as whumpfing, cracking, and recent avalanchesBe careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

A crust at the base of the snowpack will result in large avalanches if triggered. Storm slab avalanches may have the potential to step down to this layer.

Minimize overhead exposure during periods of heavy loading from new snow, wind.Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Nov 27th, 2018 2:00PM