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Avalanche Forecast

Archived

Feb 1st, 2023–Feb 2nd, 2023

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

Regions

Glacier.

Strong SW winds and rising temperatures will elevate danger levels in the Alpine, and potentially Treeline as well if wind values exceed the forecast.

Confidence

Moderate

Avalanche Summary

No new avalanche activity observed in the hwy corridor Wed.

Several human-triggered sz 1-1.5 avalanches were reported over the weekend on Avalanche Crest, Hermit Slide path, and Swiss Couloir.

A natural cornice failure triggered a size 3 deep persistent slab on the SE slope of Grizzly Peak on Saturday.

Snowpack Summary

25-30cm of low-density storm snow sits atop old wind-affected surfaces in the alpine and treeline.

The early Jan surface hoar is buried 50-80cm and is most prevalent at treeline. The November 17th facet weakness can still be found near the base of the snowpack in many areas.

Weather Summary

Strong SW winds and warming on Thurs/Fri will elevate the danger levels in the short term.

Thurs: mix of sun and cloud, Alp high -6*C, 1100m FZL, mod/strong SW winds

Fri: mainly cloudy, scattered flurries, 5cm, Alp high -5*C, 1400m FZL, moderate/strong gusty SW winds

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.