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Avalanche Forecast

Archived

Dec 17th, 2024–Dec 18th, 2024

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

Regions

Glacier.

An intense Pacific storm will crash into Rogers Pass tonight, delivering 30-40cm of snow, warming temps, and strong to extreme winds. Avalanche activity is expected through the night and into Wednesday, necessitating avalanche control.

A visit to your local ski hill to sample the new snow is recommended.

Confidence

Moderate

Avalanche Summary

Natural activity is expected to ramp up overnight and continue throughout Wed with heavy snow, warming temps, and strong/extreme winds from the West.

Avalanches have the potential to step-down to the Dec 6 surface hoar layer, which would result in large, destructive slides to valley bottom.

Snowpack Summary

Incoming snow, strong/extreme W winds, and rising temps will build a surface storm slab. This lands on variable wind slabs already present in the Alpine and at Treeline.

A persistent weak layer is down 50-70cm. This interface consists of surface hoar in sheltered locations, a sun crust on solar aspects, and continues to produce moderate-hard sudden results in test profiles.

The snowpack's base is comprised of several early-season melt-freeze rain crusts.

Weather Summary

A strong frontal system arrives tonight, bringing heavy snow, rising temps, and strong winds.

Tonight Snow, 20cm, Alp low -7°C, mod S winds, Freezing level (FZL) 900m

Wed Snow, 15-20cm, Alp high -3°C, mod/gusting extreme W winds, FZL 1500m.

Thurs Cloudy/sunny periods, isolated flurries, trace amounts, Alp high -3°C, mod S winds, FZL 1300m

Fri Cloud, scattered flurries, 5cm, Alp high 2°C, light S winds, FZL 1700m

Terrain and Travel Advice

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent 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.