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Avalanche Forecast

Archived

Feb 1st, 2015–Feb 2nd, 2015

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.
Below Treeline
Natural avalanches unlikely.

Regions

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Shallow storm slabs are possible Monday mainly near and above treeline. Watch for new snow received Sunday and Monday afternoon that has bonded poorly to old surface crusts or in areas of preserved surface hoar.

Detailed Forecast

Generally very little precipitation is expected Monday morning, with light rain and snow increasing during the afternoon along the west slopes. The Cascade Passes will locally stay cooler through Monday afternoon thanks to cool easterly flow. A frontal passage is expected later Monday afternoon, switching the Pass winds to westerly and popping snow levels up to free-air levels of 5500 ft.

Shallow storm slabs formed Sunday and Monday may have bonded poorly to old surface crusts especially near and above treeline. New storm slabs, still very shallow, may also fail on surface hoar that was recently buried on shaded aspects generally below treeline. Small loose wet avalanches can't be ruled out below treeline Monday afternoon. 

The Mt. Baker area will have a higher avalanche danger and will be broken out from the other west side zones. 

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. A frontal system crossed the PNW on Sunday, producing generally light amounts of new snow, except moderate amounts in the Mt. Baker area above 4-4500 feet. Moderate S - SW winds likely built new wind slab near and above treeline in the Mt. Baker zone as well.  

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 should mainly consist of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.

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.