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Avalanche Forecast

Archived

Feb 24th, 2021–Feb 26th, 2021

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

Regions

Yukon.

Stick to simple terrain free of overhead hazard as the next wave of storms breaks over the mountains. Up to 60 cm of aging storm snow from last weekend likely remains sensitive to human triggering and more snow with plenty of wind is incoming Wednesday Night into Thursday.

Confidence

Low - Uncertainty is due to the limited number of field observations. Forecast snowfall amounts are uncertain.

Weather Forecast

The territory continues to be in the storm track through the weekend.

WEDNESDAY NIGHT: Overnight low around -10 C, moderate to strong south/southeast wind, 3 to 8 cm of snow expected.

THURSDAY: Overcast, daytime high around -6 C, moderate northwest wind, 2 to 4 cm of snow expected.

FRIDAY: Clear skies at dawn with cloud cover building to broken throughout the day, daytime high around - 8 C, moderate southwest wind with potentially strong west wind at ridgetop, no snow expected.

SATURDAY: Broken cloud cover, daytime high around - 4 C, strong southwest wind, 2 to 5 cm of snow expected during the day with 5 to 15 cm Saturday night.

Avalanche Summary

There is evidence of a recent storm slab avalanche cycle to size 2, and slopes that have not yet avalanched are likely primed for human triggering.

This MIN report outlines conditions at the end of last weekend. 

Snowpack Summary

Last weekend's storm produced 60+ cm of new snow which rests on heavily wind affected and faceted snow in exposed terrain and perhaps a weak layer of surface hoar in sheltered areas, as found here and here. 

While our best weather stations are currently down, we have observations from Wednesday that suggest southwest wind has redistributed the aging storm snow into slabs in wind exposed terrain.

The lower snowpack is strong around White Pass, but inland areas like the Wheaton Valley likely have a thinner and weaker structure.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Stick to simple terrain or small features with limited consequence.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

Problems

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.

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.