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Avalanche Forecast

Archived

Feb 2nd, 2023–Feb 3rd, 2023

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 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.

Regions

Glacier.

Hazard will remain elevated as rising winds and temps form reactive storm slabs through out the park.

Confidence

Moderate

Avalanche Summary

Expect loose dry sluffing in steep terrain.

Thursday/Wednesday: Natural avalanche cycles throughout the highway corridor of loose and slab avalanches failing in the recent storm snow. Avalanches were mostly size 1.5-2, with isolated size 2.5-3.

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

Snowpack Summary

Warming temperatures and moderate winds will encourage slab formation in the recent 30-40cm of low-density storm snow. Below this snow is old wind-affected surfaces in the alpine/treeline and a melt freeze crust below treeline.

The early Jan surface hoar layers are buried 60-90cm 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

A break between storms on Friday, moderate to strong SW winds continue. The next storm arrives Friday night into Saturday bringing light to moderate precipitation and seasonal temperatures.

Tonight: Clear, Alp Low -6*C, Fz lvl valley bottom, Mod SW winds.

Fri: Flurries, 5 cm, Alp High -5*C, Fz Lvl 1300 m, Mod SW winds.

Sat: Flurries, 7 cm, Alp High -5*C, Fz lvl 1200 m, Mod gusting to strong SW winds.

Terrain and Travel Advice

  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Minimize exposure during periods of heavy loading from new snow, wind or rain.

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.