Avalanche Canada cgarritty, Avalanche Canada

South Coast Avalanche Forecast

Jan 15th, 2020 4:00PM

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

Continuing snowfall and potentially extreme winds will maintain dangerous avalanche conditions in the South Coast. Natural avalanche activity is expected to become increasingly widespread in wind-exposed areas.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: Increasing snowfall bringing 15-25 cm of new snow. Strong to extreme south winds.

Thursday: Cloudy with continuing flurries bringing 10-15 cm of new snow. Moderate to strong south/southwest wind, easing over the day. Alpine high temperatures around -9.

Friday: Mainly cloudy with isolated flurries and a trace of new snow, increasing overnight. Light southwest winds, increasing overnight. Alpine high temperatures around -9.

Saturday: Cloudy with snowfall bringing 15-25 cm of new snow, increasing a bit overnight. Strong south winds. Alpine high temperatures reaching -2 as freezing levels rise to 1100 metres by afternoon.

Avalanche Summary

No new avalanches were reported in the region on Tuesday or Wednesday.

On Monday two small slabs were triggered on steep features near the summit of Hollyburn.

On Sunday storm slabs were quite touchy, more details in these MIN reports. Natural storm slab avalanches with crowns up to 40 cm in depth were also reported.

Looking forward, another round of potentially heavy snowfall paired with extreme winds will ramp up avalanche danger in the region again for Thursday. Touchy storm slabs are expected to form quickly and be very reactive to human triggering.

Snowpack Summary

25-40 cm of new snow is expected to accumulate in the region by the end of Thursday under the influence of strong to extreme south winds. This will bury previously wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.

The new snow will add to about 100 cm of snow from the last few days. This previous snow has been affected by moderate to strong winds from both south and north. It rests on a hard melt hard melt-freeze crust below 1500 m. 

In some areas a weak layer of surface hoar exists above the crust. Recent snowpack tests on the North Shore have given variable, sometimes quite sudden results at this interface, particularly where this combination of crust and surface hoar was identified.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Very Likely-Almost Certain

Expected Size

1 - 2.5

Another round of snowfall and high winds over Wednesday night and Thursday will refresh storm slab problems in the region. Up to 40 cm of new snow in the forecast could bring us to 140cm above a hard crust that is present below 1500 m in elevation. There may be pockets where surface hoar sitting on this crust permits very deep storm slab releases.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Jan 16th, 2020 5:00PM