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Avalanche Forecast

Archived

Mar 10th, 2017–Mar 11th, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Olympics.

The snowpack may remain reactive and dangerous on Saturday and is only beginning the spring stabilizing process. Backcountry travel in avalanche terrain is not recommended on Saturday.

Detailed Forecast

Another front will cross the Northwest on Saturday. This will bring another day of increasing strong alpine winds and increasing rain or snow to the Olympics and Cascades. Snow levels should rise up to about 5000 feet in the Olympics.

Wind slab should be suspected mainly above treeline on all aspects but is most likely on NW to SE aspects due to recent SW to W winds. Watch for firmer wind transported snow on varied aspects especially in areas of complex terrain.

New sensitive storm slab is most likely above treeline in areas that receive more than a few inches of rapidly accumulating snowfall.

Further loose wet avalanches are most likely in the near and below treeline due to moderate to heavy rain that should affect those areas.

Avoid travel on ridges near where cornices may have formed and avoid steep slopes below cornices that may fail at any time. Cornices have been reported as large in many areas. They will have been loaded and weakened during the recent storms.

Although not listed as an avalanche problem wet slab avalanches are possible in areas that receive significant rain on Saturday.

The snowpack may remain reactive and dangerous on Saturday and is only beginning the spring stabilizing process. Higher precipitation intensities could trigger avalanches. Avalanches may step down or entrain deeper layers and be large and dangerous especially if they reach the Valentine's Day crust layer.

Backcountry travel in avalanche terrain is not recommended on Saturday.

 

 

Snowpack Discussion

Weather and Snowpack

The first week or so of March was very cool and snowy. It looks like Hurricane had about 40-50 inches of snowfall.

A strong frontal system brought increasing precipitation and winds along with a warming trend to the Olympics and Cascades on Thursday. On Thursday night rain probably pushed up to about 5000 feet in the Olympics. By Friday morning Hurricane had about .5 inches of WE which looks like it fell as rain.

Note that he snow and avalanche conditions are rapidly changing in the Olympics and Cascades!

Recent Observations

Reports by NPS rangers early Sunday 3/5 and a report listed on the NWAC Observations page indicates there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday 3/4, including the areas known as Maggies, Hurricane Hill and Sunrise Face.

The Hurricane rangers report that a snow boarder triggered a cornice release on Friday which in turn triggered a very large slab avalanche on the locally named Pit Bull path on a NE slope at about 5000 ft. A loose wet avalanche near the summit of Mt Angeles in turn triggered a large slab avalanche on S-SE slopes at about 6000 ft. Other loose wet avalanches from S-SE slopes crossed the main road below the level of Hurricane Ridge.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.