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Avalanche Forecast

Archived

Mar 7th, 2016–Mar 8th, 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.

Regions

Olympics.

Be wary of unstable layers created during periods of rapid accumulation Monday that would make shallow wind or storm slabs more likely to trigger. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. 

Detailed Forecast

Update Monday morning: The ranger at Hurricane reports 11.5 inches of new snow on Monday morning with small natural avalanches on the road cut banks. The danger forecast has be updated to considerable near and above treeline for new storm and wind slab on Monday.

Be wary of unstable layers created during periods of rapid accumulation Monday that would make wind or storm slabs more likely to trigger. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. Wind slabs are possible at higher elevations but will not be specially listed following this storm cycle. 

Cornices formed over the last week may still be weak from the recent mild weather so be aware of the overhead hazard and give cornices a wide berth while traveling along ridgelines. 

Snowpack Discussion

Weather and Snowpack

The last week has been wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds. The heaviest snowfall and precipitation occurred late Sunday 2/28 and Tuesday 3/1. The latter half of the week including the weekend has featured more rain than snow at NWAC sites along the west slopes and Olympics. With the mild temperatures this week, storm related instabilities have most likely been quick to settle out. For perspective, the averaged freezing level measured in March thus far has been 5700 ft at Forks. 

Several inches of new snow accumulated late Saturday night through Sunday with moderate southerly transport winds. 

The mid and lower snow pack along the west slopes and Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Note: The NWAC weather station at Hurricane Ridge is temporarily down due to communication issues and we hope to have it restored next week. 

Recent Observations

NPS rangers indicated widespread wind-affected snow in the Hurricane Ridge area with powdery snow in non-wind affected terrain Saturday morning. Cornices had grown fairly large and were sensitive to triggering.  

Problems

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.

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.