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Avalanche Forecast

Archived

Feb 18th, 2016–Feb 19th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

The avalanche danger should increase Friday afternoon and evening due to building wind and storm slab. Cooler temperatures should limit the loose wet problem to below treeline but wet snow hazards will continue. Change your travel plans accordingly if local conditions differ from forecasted weather and/or snowpack conditions.

Detailed Forecast

Continued periods of light to moderate snow at cool temperatures, both Thursday night and renewing during the day Friday are expected, along with strong winds.

This weather should build wind slabs on lee slopes near and above treeline, especially by Friday afternoon. Watch for firmer wind transported snow, mainly on the lee slopes facing N to SE, below ridges. 

Heavier precipitation rates Thursday afternoon and evening, and again Friday should increase the storm slab likelihood.  

Despite the cooling trend, loose wet avalanches will remain possible below treeline Friday especially on steeper southerly facing slopes. Watch for wet surface snow deeper than a few inches that usually precede loose wet avalanches or other triggered or natural loose wet avalanches.  

Snowpack Discussion

Weather and Snowpack

Dry weather with the warmest temperatures of the winter occurred February 7-10th with mild temperatures and high freezing levels. 

About 6 inches of storm snow accumulated at Hurricane Ridge a week ago Thursday to Saturday.

Rain and mild temperatures predominated Sunday and Monday with 1.5 inches of rain before a brief cooling trend brought a few inches of snow by Tuesday morning. Mild temperatures and windy conditions were seen on Wednesday.

A few inches of snow fell Thursday, 2/18 at cooler temperatures with moderate winds.  

Recent Observations

Professional NWAC observer Matt Schonwald was at Hurricane Ridge on Friday, Feb 12th. Recent warmth and persistent winds had generally created a dense and homogeneous snowpack with no layers of concern. In the Hurricane Ridge area the snowdepth falls off rapidly below 4400 feet. Bare patches and/or thin snow cover are widespread along ridges and on south to west aspects. Matt and an NPS ranger did observe 2 glide avalanches that likely occurred the night of Feb 11th. The larger one, size D2.5, released in the 20th of June path down to a smooth shale bed. However, except in isolated terrain features, glide avalanches should not be a widespread concern in the Hurricane Ridge area. 

No direct snowpack or avalanche observations have been received mid-week, but the snowpack is likely still homogenous with wet grains dominating the upper snowpack with a few inches of the latest storm snow bonding well to the old surface as of Thursday afternoon 2/18.. 

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.