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Avalanche Forecast

Archived

Feb 9th, 2019–Feb 10th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

Strong to extreme wind has formed reactive wind slabs in the last 24 hours in unusual locations and it's NOT better below treeline where a touchy persistent slab is capable of producing large human triggered avalanches. Forecaster blog here.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Cold, dry, arctic air continues to dominate the weather pattern for the foreseeable future.SATURDAY NIGHT: Freezing level at valley bottom, around -20 C in the alpine, light variable winds at all elevations, no significant snowfall expected.SUNDAY: Clear skies at dawn with cloud cover increasing throughout the day, freezing level at valley bottom, around -20 C in the alpine, light variable wind at valley bottom, light south/southwest wind in the alpine, no significant snowfall expectedMONDAY: Scattered cloud cover, freezing level at valley bottom, around -20 C in the alpine, light southerly wind at all elevations, no significant snowfall expected. A trace of snow possible Monday night.TUESDAY: Broken cloud cover, freezing level at valley bottom, around -20 C in the alpine, light variable wind at most elevations with moderate southwest wind at ridgetop, a trace of snow possible.

Avalanche Summary

On Friday a natural size 2 wind slab avalanche was observed on an east facing aspect near 3000 m. Strong to extreme wind Friday night into Saturday may have initiated a natural wind slab avalanche cycle. 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.The North Columbias are the hotspot for human triggered persistent slab avalanches as a weak layer that was buried in mid January continues to be sensitive to human triggers. This layer is touchy enough for avalanches to be triggered remotely (from a distance). SKIER AND SNOWMOBILE TRIGGERED AVALANCHES SIZE 1.5 TO 2.5 HAVE BEEN REPORTED ON ALL ASPECTS AT AND BELOW TREELINE ALMOST EVERYDAY FOR THE LAST TWO WEEKS. The bulk of this activity is occurring below 1900 m. This MIN report from Monday does a great job of illustrating the sensitivity of this weak layer.

Snowpack Summary

30-80 cm of recent new snow sits on surface hoar (feathery crystals), facets (sugary snow), wind slabs and a crust on sun-exposed slopes. In many areas, recent winds have redistributed the new snow, forming 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 50-100 cm. 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 be produce avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.