Avalanche Forecast

Archived

Feb 2nd, 2015–Feb 3rd, 2015

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.

Regions

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Storm and wind slabs remain possible Tuesday, especially on lee aspects near and above treeline. Watch for wind transported new snow received Sunday and Monday, especially higher terrain.

Detailed Forecast

Little or no precipitation is expected early Tuesday, with light rain and snow increasing in the afternoon along the west slopes.

Shallow storm slabs formed Sunday and Monday may be poorly bonded to old surface crusts, especially near and above treeline on lee aspects.

Snowpack Discussion

The weekend of Jan 24-25th, a warm and wet weather system caused high snow levels and rain and allowed for extensive snowpack settlement. Last week, high pressure aloft caused abundant sunshine and mild temperatures. This weather has now caused a thick, strong near surface crust. A series of weak frontal systems crossed the PNW on Sunday and Monday, producing generally light amounts of new snow along with moderate S - SW winds. This has likely built some areas of new wind and storm slab mainly near and above treeline. Mostly shallow wet snow conditions exist below treeline.

On Monday in the Stevens Pass area, shallow, but touchy loose wet avalanches were noted by NWAC observer Jeff Ward..

Prior to the Sunday's system, the snowpack was dominated by strong surface crusts, limiting the avalanche potential. There had been surface hoar growth last week on shaded terrain mainly below about 5000 feet, along with some near surface faceting(NSF) on non-solar slopes. Surface hoar/NSF were likely buried by the light snowfall and initial cool temperatures Sunday.

See Jeff's video from the Steven's Pass area below.

The snowpack west of the crest mainly consists of the generally shallow recent storm snow over stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.

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.