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Avalanche Forecast

Archived

Mar 27th, 2014–Mar 28th, 2014

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

Regions

Olympics.

The likelihood of triggering shallow new storm slab near and above treeline especially on lee slopes and wet loose avalanches at lower elevations on all aspects should increase Friday.  

Detailed Forecast

A Pacific frontal system approaching from the west should bring increasing rain and snow along with rising winds and snow levels Thursday night through Friday.  While not strong by Pacific Northwest standards, this weather system should cause an increase in the avalanche danger during the day as shallow storm and wind slab build denser snow over initially colder and lower density snow from the morning.  Expect the highest precipitation totals on the southern slopes of the Olympics Friday. 

Rising snow levels will also mean the potential for rain at lower and mid elevations and the increasing chance for generally shallow wet loose on all aspects throughout the day. 

Remember to evaluate snow and terrain carefully throughout Friday. Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches.  Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences. 

New or recent small areas of wind slab should also be possible Friday mainly above treeline on lee slopes. Watch for signs of cracking or firmer wind transported snow.  

Snowpack Discussion

Last weekend some shallow wind slab on lee slopes near and above treeline was reported as stubborn, but reactive to ski tests last Sunday, as noted by professional observer Katy Reid.  Also noted last Sunday were loose dry slides on shaded slopes and loose wet avalanches on solar aspects. Much warmer weather and sunshine late Sunday and Monday likely produced more widespread wet slides by Monday.  

Cooling and a frontal passage Tuesday deposited about 8-12 inches of new snow in the north Olympics as of Wednesday morning.  Showers Wednesday afternoon and night added a few inches to these storm totals.  Winds near tree line have remained relatively light, however stronger winds above treeline may have formed new shallow wind slab on lee slopes from NW through SE aspects.  Light showers at moderate snow levels were seen on Thursday. 

 

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.