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Avalanche Forecast

Archived

Feb 19th, 2020–Feb 20th, 2020

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

Regions

Lizard-Flathead.

The sun is getting higher in the sky at this time of year and can pack a punch so be ready to step back from steep south aspects showing signs of solar warming.

Confidence

High -

Weather Forecast

Wednesday night: Clear. Light southwest winds. Alpine low -16 C. Freezing level 1000 m.

Thursday: Sunny. Light west wind increasing to strong at ridgetop. Alpine high -2 C. Freezing level 1300 m.

Friday: Sunny. Moderate west wind, strong at ridgetop. Alpine high -2 C. Freezing level 1400 m.

Saturday: Sunny. Moderate west wind, strong at ridgetop. Alpine high -1 C. Freezing level 1500 m.

Avalanche Summary

Explosive control work Monday and Tuesday produced mostly size 2 cornices, some triggering thin slabs on slopes below.

There have been two reports of avalanches running on the early February rain crust. Explosive control work produced a size 2 with crown depth up to 80 cm on Tuesday. A skier triggered size 2 on a southeast aspect is described in this MIN report from Sunday.

Snowpack Summary

A thin sun crust may be found at the surface on steep solar aspects. Variable wind affect in the alpine and near treeline with soft slabs in immediate lees.

A thick rain crust sits 30-60 cm below the surface, up to 2100 m. Recent avalanche activity has been observed at the faceting interface between this crust and overlying snow.

The bottom 20 cm of the snowpack consists of basal facets and decomposing crusts that have not been an active avalanche problem since December, but could reemerge as a problem after sustained warming.

Terrain and Travel

  • Avoid exposure to slopes that have cornices overhead.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.