Avalanche Forecast

Archived

Feb 12th, 2016–Feb 13th, 2016

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Shallow wind slab avalanches are possible Saturday on lee slopes mainly near and above treeline. A warming trend during the day Saturday will increase the likelihood of unstable storm slab layers.

Detailed Forecast

Light snowfall accumulations are expected Friday night through Saturday above 4000 feet in the Olympics. SW winds will transport new snowfall onto lee slopes. While new snow may bond well to moist snow surfaces and various crusts, a warming trend on Saturday increases the likelihood for unstable storm layers in the shallow new snow.

Heavier precipitation and a warming trend is expected Saturday night and should result in an increased avalanche danger on Sunday.

Snowpack Discussion

Weather and Snowpack

A large upper ridge and warm air mass aloft over the West Coast from this past Sunday through Wednesday led to the warmest weather of the winter. During this stretch temperatures were generally well above freezing. After some light rain Thursday afternoon and night, rain changed to light snow showers with sunbreaks by late Friday morning at Hurricane Ridge.

Professional NWAC observer Matt Schonwald was at Hurricane Ridge on Friday. Recent warmth and persistent winds have generally created a dense and homogeneous snowpack without any layers of concern. In the Hurricane Ridge area the snowdepth falls off rapidly below 4400 feet. Bare patches or thin cover are widespread along ridgelines and south through west aspects. Matt and a NPS ranger did observe 2 glide avalanches that likely occurred Thursday night. The larger one, size D2, released in the June 20th path down to a gravel bed. However, except in isolated terrain features, glide avalanches should not be a widespread concern in the Hurricane Ridge area.

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.