Avalanche Forecast

Issued: Feb 10th, 2019 4:41PM

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

dsaly, Avalanche Canada

South Columbia.

Watch for wind slabs in unusual locations. Conditions are trickier at treeline and below where buried surface hoar is still capable of producing large human triggered avalanches. Check out the Forecaster Blog here.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

SUNDAY NIGHT: Clear periods. Alpine temperatures near -18C. Ridgetop winds light from the south.MONDAY: Mix of sun and cloud with isolated flurries, trace accumulation. Alpine temperatures near -15C. Ridgetop winds light from the south.TUESDAY: Cloudy with scattered flurries, 5-10 cm accumulation. Alpine temperatures near -10C. Ridgetop winds moderate from the south.WEDNESDAY: Cloudy with scattered flurries, 5-10 cm accumulation. Alpine temperatures near -8C. Ridgetop winds light to moderate from the southeast.TUESDAY: Broken cloud cover, freezing level at valley bottom, around -20 C in the alpine, light variable wind at most elevations with moderate to strong southwest wind at ridgetop, a few centimeters of snow possible.

Avalanche Summary

Strong to extreme wind Friday night into Saturday initiated a natural wind slab avalanche cycle. Wind slab avalanches to size 2.5 were reported on all aspects and occurring above 2000 m. Check out this MCR report of a skier triggered wind slab from an east facing aspect at 2370 m in the adjacent Glacier National Park region on Saturday.A persistent weak layer that was buried in mid-January continues to be reactive to human triggers. This layer is sensitive enough for avalanches to trigger remotely (from a distance). Activity on this interface continued through Friday as skiers triggered avalanches to size 1.5 on north through northeast facing terrain between 1650 and 1900 m. At higher elevations (2000-2300 m) small wind slabs were reactive to skier traffic on all aspects including a size 2 skier triggered avalanche on a west aspect while skiing over a roll.Human triggered avalanches size 1.5 to 2.5 were widespread last week on a variety of aspects at treeline and below.

Snowpack Summary

20-70 cm of recent new snow sits on wind slab, surface hoar (feathery crystals), facets (sugary snow) and a crust on sun-exposed slopes. In many areas, recent winds have formed wind slabs on all aspects due to shifting wind directions. The most notable feature in the snowpack at this time is a persistent weak layer that was buried in mid January, which is now buried 40-90cm. This layer consists primarily of surface hoar, however there is also a crust associated with it on sun-exposed slopes. This layer is the most prominent at treeline and below, and continues to produce avalanches.

Problems

Wind Slabs

20-70 cm of old storm snow continues to be redistributed by arctic wind out of the north and east. Wind slabs forming at treeline have the potential to step down to the buried surface hoar resulting in large avalanches.

Wind from a variety of directions has formed wind slabs in unusual locations at and above treeline.Avoid freshly wind loaded features.If triggered, wind slabs may step down to deeper layers and result in even larger avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

40-90 cm of snow sits above a weak layer of surface hoar (feathery crystals) and crust. This layer continues to be reactive to human triggers. The trees are not a safe haven right now, in fact, treeline may be the most dangerous elevation.

Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Any steep opening in the trees should be treated as suspect.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 11th, 2019 2:00PM