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Avalanche Forecast

Archived

Feb 8th, 2017–Feb 9th, 2017

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

Regions

Olympics.

A mixed bag of avalanche problems should be expected on Thursday. Back country travel in avalanche terrain is not recommended through Thursday morning.

Detailed Forecast

A strong wet warm front will lift north over the Olympics and Cascades on Wednesday night to Thursday morning. Plan on rapid warming Wednesday night and heavy rain or snow with higher snow levels through Thursday morning. This should cause an avalanche cycle in the Olympics and Cascades which should test the snowpack. Small avalanches may step to deeper layers during the cycle.

A mixed bag of avalanche problems should expected on Thursday with wind slab and storm slab very likely at times in the above treeline band and loose wet avalanches very likely in the below treeline band with some over lap in between in the near treeline band. Back country travel in avalanche terrain is not recommended through Thursday morning.

Wet slab avalanches and cornice failures should also be likely in areas with heavy rain Wednesday night to Thursday morning.

The cold front should cross the Cascades Thursday late morning or midday. This should cause a change to showers and lowering snow levels. The avalanche danger should begin to decrease following the cold front Thursday afternoon.

  

Snowpack Discussion

Weather and Snowpack

A strong storm cycle was seen Friday through Monday with about 3 feet of snow accumulating at Hurricane. A cooling trend began Friday afternoon with a gradual decrease in overall snowfall intensities by Sunday morning.

High clouds and cool temperatures and some sunshine Tuesday has allowed for recent storm snow to settle and stabilize, as evidence by the 6 inches of snowpack settlement during the day Tuesday at the Hurricane Ridge study plot.

The older underlying snowpack should be settled and stable at Hurricane.

Increasing winds, snowfall and warming were generally seen on Wednesday as the next storm approached. 

Recent Observations

NWAC pro-observer, Matt Schonwald was at Hurricane last Friday (before most of storm snow arrived) and found scoured slopes or shallow new snow on E slopes and shallow building wind slab on SW slopes. He found no significant signs of instability, ski tracks still visible from last week and lots of surface roughness to fill in on lee slopes.

No observations were received since Saturday. 

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.

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.