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Avalanche Forecast

Archived

Mar 18th, 2017–Mar 19th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

The avalanche danger should decrease Sunday as a wet snowpack refreezes. Fresh but shallow wind slab will mostly likely be found above treeline. Shallow loose wet slides are likely on steeper solar aspects in the afternoon.

Detailed Forecast

Decreasing snow showers along with rapid cooling Saturday night through Sunday morning should transition to mostly sunny skies by Sunday afternoon. Freezing levels will be on the cool side Sunday but late March sunshine will help bump up temperatures to near or above freezing at lower and mid-elevations. Winds are forecast to be fairly light on Sunday.

The avalanche danger should decrease Sunday as a wet snowpack refreezes.

Generally small loose wet avalanches are likely at lower elevations and on solar slopes. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases.

Fresh but shallow wind slabs have likely built on NW to SE aspects, mainly above treeline. Watch for firmer wind transported snow on other aspects, especially in areas of complex terrain.

Although the likelihood of wet slab or glides avalanches has greatly decreased with the cooling trend, these avalanche problems may still occur 24 to 48 hours following a heavy rain event. Continue to avoid unsupported slopes, especially where you know there is a smooth underlying surface or slopes with glide cracks. Wet slab or glide avalanches will not be listed as an avalanche problem in the Olympics due to less rainfall and increased cooling versus areas in the Cascades. 

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. 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 was seen 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. 

Recent Observations

NPS rangers at Hurricane Ridge reported about 5 inches of wet snow Saturday morning with little sign of recent wind transported snow. 

Problems

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.

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.