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Avalanche Forecast

Archived

Dec 27th, 2022–Dec 28th, 2022

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

Regions

Glacier.

Underneath the new storm snow lurks a weak, sugary snowpack...and that sugar ain't sweet, if you know what I mean!

There may be some significant settlement of the snowpack in the coming days, with whumpfing and shooting cracks alerting you to dangerous conditions.

Confidence

Moderate

Avalanche Summary

Natural avalanche activity has reduced with the decreased snowfall/winds.

Artillery control on Xmas and Boxing Day had good results, with many avalanches observed in the sz 2.5-3.5 range. There was evidence of step-down avalanches on the persistent weak layers.

Be suspicious of slopes that do not appear to have avalanched in the last few days.

Snowpack Summary

The Xmas storm came in windy and warm, and now this dense, heavy storm slab is squishing down a below-average depth, weak, faceted snowpack.

The storm slab interface (down 55-65cm) was reactive in snowpack tests, while the persistent weak layers (PWLs) were stubborn in tests today at Fidelity.

The reaction of the PWLs to the overlying burden is the thing to watch the next few days. Dig down and test them.

Weather Summary

A gradual cooling and clearing trend sets up for Rogers Pass for the rest of the week.

Tonight: flurries, 5cm, Alp low -6*C, light SW winds, 1200m FZL

Wed: scattered flurries, trace snow, Alp high -6*C, moderate W winds, 1200m FZL

Thurs: sunny periods, trace snow, Alp high -9*C, light SW winds, 700m FZL

Terrain and Travel Advice

  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Storm slabs in motion may step down to deeper layers resulting in 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.