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Avalanche Forecast

Archived

Feb 27th, 2017–Feb 28th, 2017

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

Regions

Olympics.

Watch for fresh shallow wind slabs, mainly near ridges or cross loaded features near and above treeline. Fast moving loose-dry avalanches continue to be a problem in many areas, especially in steep terrain of consequence.

Detailed Forecast

A break between disturbances is expected during the day Tuesday before the next weather system arrives Tuesday afternoon. Cold temperatures, light winds and increasing light snow showers by late Tuesday afternoon, should allow for recent storm snow to very slowly settle. 

Watch for fresh, generally shallow wind slabs on lee aspects and cross loaded features. Any recently formed wind slabs should mainly be confined to the terrain above treeline, but in some areas wind slabs may have formed in the upper elevations of the below treeline, so evaluate the snow and terrain carefully Tuesday.

Watch for loose dry avalanches on steeper slopes in non-wind affected terrain. Be especially wary of fast running loose dry avalanches near terrain traps. 

Give cornices a wide berth when traveling along ridgelines and avoid lingering on slopes below cornices as they may fail at any time.

Snowpack Discussion

Weather and Snowpack

Heavy rain to high elevations arrived on Valentines Day 2/14 and subsequently formed the uppermost, very strong rain crust within the snowpack. 

A pair of storms deposited about a foot of snow in most areas by Monday 2/20. This was combined with periods of moderate to strong W-SW winds, forming wind slabs at the time. A slightly unstable weather pattern last week caused a mix of sun and light snow showers with sun crusts forming on solar aspects.

Cool NW flow has brought an additional 8-10 inches of snow in a snow showers from Saturday through Monday, with cold temperatures and generally light winds.  NPS Rangers reported that the most recent rain crust was supportable in many areas and aspects around Hurricane Ridge.

Older wind slabs have stabilized while generally 10-15 inches of low cohesion snow over the crust have made for some nice touring conditions of late. 

Recent Observations

No observations have been received from the Olympics in the past few days.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.