Avalanche Forecast

Issued: Dec 19th, 2017 4:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Loose Dry.

grant statham, Parks Canada

Little Yoho.

An upslope storm is crossing the region tonight with additional snow and strong east winds. More snowfall is expected in areas to the east (Banff Park). Be wary as additional load develops over the Dec 15 persistent weak layer.

Summary

Weather Forecast

Northeast flow affects the regions tonight with another 10-15 expected, mostly in the southern part of the forecast region (SSV). Less snow north (Bow Summit). N and E winds up to 70 km/hr expected overnight, with temperatures remaining cool at -12 to -15. Storm ends Wednesday morning with scattered flurries through Thursday. Sunshine for Xmas...

Snowpack Summary

10-30 cm of soft snow now covers the Dec 15 persistent weak layer of surface hoar, sun crust or facets (depending on location). An additional 5-10 cm and strong NE winds are expected overnight Tuesday and may create windslabs in unusual locations (reverse loading). These will be very sensitive to triggering soft slab avalanches.

Avalanche Summary

Widespread small soft slab avalanches were observed on Monday, and to a lesser extent on Tuesday at the local ski areas. Generally these have been size 1 avalanches with little mass, but we expect their size to grow with the additional snow. Loose snow avalanches have also been observed in steep gullies.

Confidence

Forecast snowfall amounts are uncertain on Wednesday

Problems

Wind Slabs

Strong NE winds will easily transport the 25 cm of recent snow into windslabs on S and W aspects (backwards from usual). Avoid freshly wind loaded rolls and slopes and study the snowpack distribution from this upslope storm.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Loose Dry

Climbers in steep gullies be prepared for spindrift and loose snow running down the climb. Put in lots of ice screws. Any avalanches will likely be small, but could knock you off your feet.

Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 1

Valid until: Dec 20th, 2017 4:00PM