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Avalanche Forecast

Archived

Jan 1st, 2015–Jan 2nd, 2015

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

Regions

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Carefully evaluate steep slopes still showing signs of firmer wind transported snow from early this week. Snowfall should be light by the end of the daylight hours on Friday and not cause a great change in conditions. But use more caution if snowfall is greater than expected.

Detailed Forecast

A weak cold front will move northwest to southeast over the Olympics and Cascades Friday afternoon and night. This should cause increasing northwest winds Friday in most areas. Light rain if any should quickly change to light snow due to a rapid cooling trend. The main light snow should be seen in the Olympics and north Cascades Friday afternoon spreading to the south Cascades Friday evening with little making it to Mt Hood Friday night.

The light amounts of snow in the Olympics and Washington Cascades should not greatly change snow conditions. Any new storm slab should be mainly in the Olympics and in the north Cascades, small and shallow, and will be rated as unlikely.

Watch for lingering wind slab from early in the week where the northeast winds redistributed snow mainly above and near treeline.

Sun crusts are also likely on steep south slopes where sun warmed snow from Thursday refreezes on Friday.

Snowpack Discussion

A storm system hit the Northwest last weekend with strong west to northwest winds. NWAC sites west of the crest picked up about 6-22 inches of storm snow with a good cooling trend.The least fell at Snoqualmie Pass due to initial very wet snowfall. Rapid loading caused storm slab during and after this storm which is expected to have since stabilized.

Strong northeast winds hit at the tail end of the storm Monday and Tuesday. Regionally this transported snow and formed some local wind slab on exposed slopes and near ridges but this layer in most areas bonded well and lacked weak layers.

Wind affected surface snow on Wednesday on a NWAC/WSDOT field trip to the weather station at Chinook Pass by Dennis D'Amico.

An upper ridge tilted inland yesterday and today producing sunny weather with warming at higher elevations. But Arctic air at the surface east of the crest and offshore surface flow is still producing cold temperatures at lower elevations in the Cascade passes and east of the crest Thursday.

Wednesday and Thursday right side up powder is providing great conditions on sheltered shaded slopes. The warming and sunshine has been causing some snowballing and small wet loose avalanches on steep slopes facing the sun.

A generally strong mid and lower snowpack is expected to be preventing deeper instabilities. There was one report of a persistent weak layer near an older crust at Stevens Pass a few days ago. But no known avalanche activity has occurred on this layer west of the crest.

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.