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Avalanche Forecast

Archived

Feb 14th, 2020–Feb 17th, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

North Rockies.

It's time to back off this weekend as new snow & wind continue to fuel storm slabs that are expected to remain sensitive to both human and natural triggering. Stick to simple avalanche terrain and avoid overhead hazard. Careful in the trees, buried weak layers exist there too.

Confidence

High -

Weather Forecast

We’re in store for another stormy weekend in the North Rockies.

FRIDAY NIGHT: Freezing level at valley bottom, moderate to strong southwest wind, 15 to 20 cm of snow expected.

SATURDAY: Overcast, freezing level at valley bottom, moderate to strong west/northwest wind, 5 to 15 cm of snow expected.

SUNDAY: Broken cloud cover, freezing level at valley bottom, light to moderate west/northwest wind, 5 to 10 cm of snow expected.

MONDAY: Broken cloud cover, freezing level at valley bottom, moderate west/northwest wind, trace of snow possible.

Avalanche Summary

Throughout the storm there has been a widespread natural avalanche cycle to size 2 within the storm snow. Continued snow and wind are expected to continue to fuel this avalanche cycle.

Snowpack Summary

Wednesday, Thursday and Friday produced 50 (Kakwa) to 100 (Torpy) cm of storm snow under mild temperatures and moderate wind from the south, southwest and southeast. Easy sudden planar shears and wide spread storm slabs have been observed in all of the new snow. The presence of buried surface hoar about 50 cm below the surface has been confirmed in both the Pine Pass and Torpy zones, it may be more widespread throughout the region too. 

Below all the recent storm snow there is a thin rain crust from the warm, wet storm on Feb 01. This rain crust has been reported to exist up to treeline elevations around 1700 m. Initially this layer was described as reactive and was the focus of a number of avalanches. With up to a meter of new snow on it it could become active again this weekend.

Deep in the the mid-pack there may still be a layer of surface hoar buried in late December. It's gaining strength, but should remain a concern since snowpack tests still demonstrate this layer has the potential to slide, albeit in isolated areas and/or with very large triggers.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Be aware of the potential for remote triggering and large, deep avalanches due to the presence of buried surface hoar.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Cornice failure may trigger large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.