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Avalanche Forecast

Archived

Dec 24th, 2013–Dec 25th, 2013

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

Snoqualmie Pass.

Detailed Forecast

Mostly sunny days and fair nights are expected except some low clouds or fog in the lower elevation valleys. Winds should remain light with mild temperatures at higher terrain Christmas Day. This should allow for some surface snow melt on sun exposed terrain. Some shallow wet snow conditions may develop by late morning or afternoon on some of these steep sun facing slopes where caution should be exercised.  Previously formed wind slab near ridges should also continue to slowly stabilize. 

Snowpack Discussion

Warm wet weather December 13-14th followed by dry weather with high freezing levels helped to form crust layers and stabilize earlier persistent buried weak layers from earlier in December. Most recently a series of fronts over the past four days caused additional precipitation, mostly at moderate freezing levels causing rain or wet heavy snow at mid and lower elevations while depositing 30-60 cm (1-2 ft) of storm snow over most areas along the west slopes and volcanic peaks. This storm cycle while not powerful for northwest standards as caused some recent avalanche activity ranging from wet slabs, loose wet, storm slabs and wind slab releases.

Most recently on Monday 12/23 widespread natural and triggered wind slab releases where seen in the Mt Baker area. The slab releases ranged mostly from 40-60 cm (18-24 inches) and ran long distances with some sympathetic releases triggered remotely. These size 1.5-2 slides released on wind loaded northerly facing slopes below ridges but were extensive. 

A wet slab was reported below Chair Peak in the Alpental Valley Sunday near midday and ran a far distance.

Fluctuating freezing levels over the past several days was followed by a cold front late Monday that brought significant cooling by Monday night and early Tuesday. This cooling has likely helped to strengthen and consolidate previous wet snow or unstable storm slab layers helping to lower the current overall danger.     

Watch for areas where a locally deeper snow pack may exist. The most likely areas to find unstable conditions would be on steep generally northerly to east facing terrain below ridges and near or above tree line. These would be the areas most likely to have formed wind slab.  

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.

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.