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Avalanche Forecast

Archived

Mar 20th, 2017–Mar 21st, 2017

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

Regions

Olympics.

Above treeline, the avalanche danger should slightly increase Tuesday due to shallow fresh wind slabs near ridges. At lower elevations, shallow wet snow conditions should maintain the possibility of loose-wet avalanches. Watch for overhead hazard, such as recently formed large cornices.

Detailed Forecast

A weak disturbance will spread increasing light rain and snow at gradually rising freezing levels overnight Monday. Only light amounts of precipitation are expected overnight. This should begin to wet and weaken shallow surface snow layers.

Another band of moisture Tuesday should bring periods of generally light rain and snow at moderate freezing levels.  Southerly winds should be moderate along the ridges Tuesday.

These conditions should build some shallow fresh wind slabs at higher terrain along ridges, mainly on NW-NE-E facing terrain. Watch for firmer wind transported snow on all aspects, especially in areas of complex terrain. 

At lower elevations, light rain should maintain shallow wet snow conditions and make loose-wet snow avalanches possible.

Avoid areas with terrain traps where a small loose wet avalanche could have unintended consequences. 

It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.

Snowpack Discussion

Weather and Snowpack 

The first week or so of March was very cool and snowy. NWAC stations along the west slopes of the Cascades and Olympics piled up about 3 to 8 ft of snow with the most at Mt Baker.

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately these systems delivered far more rain than snow. At least two regional avalanche cycles occurred during the stretch including a very active avalanche cycle in the Hurricane Ridge area 3/9 through 3/10 with large or very large natural and human-triggered avalanches reported. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. 

After a short respite from the active weather pattern on Thursday, another strong low pressure system brought several inches of rain to the west slopes of the Cascades and Olympics. Several inches of snow accumulated early Friday night before continued warming pushed snow levels above Hurricane Ridge with moderate rain seen through early Saturday morning. Rapid cooling later Saturday morning was followed by generally light snow showers with little in the way of new snow accumulation. Sunday was cool with light winds and mostly sunny skies.

Recent Observations

NPS rangers at Hurricane Ridge reported about 5 inches of wet snow Saturday morning with little sign of recent wind transported snow.  A public observation from the Obstruction Point Road noted ongoing wind transport, a supportable rain crust and lingering giant cornices along N-NE aspects of ridge-lines Saturday. 

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.