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Avalanche Forecast

Archived

Mar 24th, 2016–Mar 25th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

Olympics.

The avalanche danger will vary in the Olympics based on recent snowfall and wind affects seen since Wednesday night. Fresh wind slab will continue to be a primarily hazard on Friday near and above treeline. Loose snow avalanches will be likely on steeper slopes. Human triggered storm slabs are possible as new snow becomes more cohesive with daytime warming on Friday. 

Detailed Forecast

Orographic showers in cool NW flow aloft Thursday night will wind down Friday morning followed by with partial clearing in the afternoon. The avalanche danger will vary in the Olympics based on recent snowfall and wind affects seen since Wednesday night.    

Fresh wind slab will continue to be a primarily hazard on Friday near and above treeline. By avoiding obviously wind loaded slopes, you can enjoy some fine late season conditions. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

We will flip which loose snow avalanche we identify as the primary problem with more sunshine expected Friday afternoon versus Thursday. Loose wet avalanches will be likely on steeper solar slopes by mid-day or afternoon. Loose dry avalanches should be small but likely on steeper non-solar slopes. Be aware of terrain traps where even a small loose avalanche could have unintended consequences in the wrong terrain.    

Human triggered storm slabs are possible as new snow becomes more cohesive with daytime warming on Friday. Watch for graupel layers received Thursday night to become potential bed surfaces for storm slabs. 

Recently formed cornices have grown large. If traveling along ridgelines, be aware that cornices break much further back than expected and you don't want to go for a ride with a chunk of cornice. Despite the cool weather, cornice releases can be unpredictable during the spring.

Snowpack Discussion

Weather and Snowpack

About 2-3 feet of snowfall accumulated at Hurricane March 9-15th.

A combination of sun, mild temperatures and then some rain was seen for several days ending about Sunday 3/20. This weather caused about 10 inches of consolidation of the recent snow at Hurricane which is usually a sign of a strengthening snowpack.

Older winter avalanche problems of wind and storm slab in the Olympics will have mostly settled and stabilized during the mild weather.

A low pressure system crossed the Northwest on Monday and Tuesday. NWAC stations along the west slopes and Hurricane Ridge accumulated a few inches above 4000 feet during this time. Light rain was seen on Wednesday in the below treeline band before a cold front swept through Wednesday night. About 3-6 inches of snow accumulated above 3500 feet Wednesday night and Thursday. 

Frequent March storms have built large cornices along ridges in many areas.

The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

No recent observations have been received since last weekend. It is not known if west winds Wednesday night and Thursday have built new wind slab to the same degree near and above treeline as seen along the west slopes of the Cascades. 

Hurricane Weather Station

Internet communications were restored to the station on 3/23!  Thank you for your patience. 

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.

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.