Avalanche Forecast

A frontal system should spread increasing rain and snow at gradually rising freezing levels Monday along with strong ridgetop winds. This weather system should cause a significant increase in the danger through the day Monday.  Given the variety of weak surface snow conditions, including surface hoar, weak near surface faceted snow or previously deposited weak low density snow any significant storm snow should lead to sensitive slab avalanches as surface conditions become effective for slab avalanche propagation.

These slabs should develop from increasing density storm snow and also from wind transported wind slab.  Watch for more significant storm and/or wind transported snow by Monday as avalanche danger may increase rapidly if loaded by significant new snow.  

Manage the terrain by avoiding wind loaded lee slopes and any steep open terrain being loaded by significant storm snow, especially near and above tree-line. Watch for shooting cracks as a sign of instability. Even a small wind slab in the wrong terrain, i.e. above cliffs or very steep slopes, could have unintended consequences. 

A storm arrived at the end of January with rising snow levels and rain above 6000 feet for the Olympics before transitioning to snow and colder temperatures. Wind was less of a factor with this event with a more even distribution of storm snow and a general lack of wind slab during the storm cycle. Only about 1-3 inches of additional snow has accumulated in early February. 

Very cold temperatures this week have produced strong temperature gradients in the upper portion of the snowpack. The strong temperature gradient has allowed surface hoar to form, as well as developing weak near surface faceting and causing some breakdown of recently buried crusts.  In addition the cold temperatures have produced weak faceted crystals above the buried melt-freeze crust (see recent images and video below).  

Surface hoar crystals on N. aspect Klahhane Ridge, Olympics, Friday Feb 7, 2014. Photo, Katy Reid

Faceted crystals above buried crust on N. aspect Klahhane Ridge, Olympics, Friday Feb 7, 2014. Photo, Katy Reid

Moderate east to southeast winds in the Cascades built new wind slab during the week, while winds were much lighter over the Olympics.  Field reports from NWAC pro observers Friday near Hurricane Ridge indicated that new wind slab layers were very isolated to some ridges while most surface snow remained unconsolidated hence lacking the cohesion to produce slab avalanche propagation.

The current weak surface snow structure should rapidly become dangerous when loaded by either additional wind transported snow or warmer more dense storm snow.  see video from Friday Feb 7th: https://www.youtube.com/watch?v=anGcxdg4jfs

Regionally the avalanche danger is lower near Hurricane Ridge than in the Washington Cascades where a more diverse snowpack exists. See the Cascades forecast if traveling there.

The mid and lower snowpack consists mainly of crusts and melt form crystal layers which have generally not been reactive to to snow pit tests. Low snow amounts are continue to limit the avalanche danger on many south slopes and at low elevations due to terrain and vegetation anchors.