Avalanche Forecast

Archived

Nov 27th, 2016–Nov 28th, 2016

Alpine

Natural avalanches possible, human triggered probable.

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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Avalanche problems should be found in new snow layers on Monday.

Detailed Forecast

A snowy system is headed our way Sunday afternoon to Monday. This will cause some strong alpine winds and should be a good snow producer especially for the Cascade west slopes.

Slowly decreasing northwest flow should carry a cool, slightly unstable air mass and snow showers to the Olympics and Cascades on Monday. The west slopes will continue to be favored and convergence is likely in the central Cascades.

Any avalanche problems should be found in new snow layers. Watch for signs of firmer wind transported snow that indicate wind slab. Storm slab is most likely in areas that rapidly accumulate more than several inches of new snow.

While this forecast is for a moderate avalanche danger mainly above tree line the report above sure indicates you better be watching for potential wind slab. The potential for triggering does not seem great but such an avalanche can have bad consequences. Remember to watch for signs of firmer wind transported snow

A cooling trend should help give favorable right side up new snow profiles in sheltered areas where new snow does not accumulate too rapidly or too deeply.

There currently aren't any indications of persistent weak layers in the snowpack along the Cascade east slopes.

In most areas in the below treeline band there is not enough snow yet for avalanches. Any avalanche problems would be only in the upper part of this band.

Snowpack Discussion

Weather Discussion for the Cascade East Slopes

A weakening front with a lot moisture flowing south to north along the frontal boundary moved slowly into the Northwest with a warming trend late Friday and Saturday. There a brief break by Sunday morning with a cooling trend but the next front is beginning to arrive on Sunday afternoon. Generally light amounts of new snow were seen along the Cascade east slopes on Saturday morning and Sunday morning.

Recent Reports for the Cascade East Slopes

There is little in the way of recent reports for the Cascade East Slopes. However on Friday a skier triggered a deep wind slab on a 40 degree northwest slope at about 7500 feet on Slate Peak near Harts Pass. The crown varied from about 2 to 7 feet and ran about 2-300 vertical feet with car sized chunks of debris. Fortunately the skier was not caught. He noted that windward slopes across the valley were scoured indicating recent wind transport.

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.