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Avalanche Forecast

Archived

Mar 8th, 2020–Mar 9th, 2020

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

Regions

Lizard-Flathead.

Storm slabs and loose avalanches were touchy Sunday and are expected to remain that way Monday as the storm snow feels the strong March sun for the first time. The new snow needs a bit of time to stabilize before we start gunning for the bigger objectives.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Enjoy the sun Monday.

SUNDAY NIGHT: Freezing level at valley bottom, light southwest wind, trace of snow possible.

MONDAY: Clear skies, freezing level rising to about 1300 m, light southwest wind, no significant precipitation expected.

TUESDAY: Clear skies in the morning becoming cloudy after lunch, freezing level rising to about 1600 m, moderate west/southwest wind, no significant precipitation expected during the day, potential for 5 to 10 cm of snow at upper elevation Tuesday night.

WEDNESDAY: Broken cloud cover, freezing level holding at 1500 m, light west/northwest wind, trace of snow possible.

Avalanche Summary

On Sunday loose dry and soft slab avalanches were sensitive to human triggering and control work to size 1.5. Avalanches have been 10 to 20 cm in depth, running fast and far. The storm snow is expected to remain sensitive to human triggering Monday.

Snowpack Summary

The Friday/Saturday storm produced 20 to 35 cm of new snow which buried heavily wind affected surfaces in exposed areas as well as a sun crust that is present to ridge top on solar aspects. Temperature crusts extend up to 1900 m on other aspects. This storm snow has not yet bonded to the old surfaces and is touchy.

A thick rain crust that has facets associated with it sits 30-60 cm below the surface and can be found up to ridgetops. We have only seen one avalanche on this layer since February 17th. The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • The new snow could use a day or two to settle and stabilize before we start to tee up the bigger lines.
  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Extra caution is needed around cornices under the current conditions.

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.