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Avalanche Forecast

Archived

Dec 26th, 2022–Dec 27th, 2022

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

The new, heavy storm slab is overloading the weak, early-season facets, resulting in a natural avalanche cycle.

There will be significant whumpfing, settling, and remote triggering of avalanches over the next few days.

Stick to conservative terrain choices and manage your overhead hazards wisely!

Confidence

Moderate

Avalanche Summary

A large natural avalanche cycle ripped through Rogers Pass Xmas Eve. Numerous avalanches from sz 2 to 3-3.5 were observed from Tupper, Macdonald, and other highway paths.

Artillery control on Xmas and Boxing Day left deposits on the highway as well, with evidence of step-down avalanches on the persistent weak layers.

Avalanches have significant potential to increase in size once they gather up the lower elevation facets and persistent weak layers.

Snowpack Summary

Up to 60cm of new snow/storm slab sits on a generally weak and facetted snowpack.

There are several persistent weak layers buried, which are most prevalent at and near treeline. These layers can be found ~60cm (Dec 16 surface hoar), ~80cm (Dec 5 surface hoar), and ~100cm (Nov 17 surface hoar/suncrust/facets) below the surface. They are responsible for the significant whumphing under your feet, as well as the large avalanches above you in the mountains.

Weather Summary

Here it comes, more sloppy snow!! A warm Pacific front marches through our area, bringing high freezing levels (FZL), gusty winds, and moisture.

Tues: snow, 15cm, Alp high -1*C, moderate SW winds, 1800m FZL

Wed: scattered flurries, 5cm, Alp high -5*C, moderate W winds, 1300m FZL

Thurs: sunny periods, trace snow, Alp high -10*C, light winds, 500m 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.