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Archived

Avalanche Forecast

Dec 19th, 2017–Dec 20th, 2017
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Banff Yoho Kootenay.

An upslope storm is crossing the region tonight bringing more snow to southern areas and strong east winds. Be wary as additional load develops over the Dec 15 persistent weak layer.

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

Avalanche 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