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Avalanche Forecast

Archived

Nov 27th, 2016–Nov 28th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

Olympics.

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.

Slowly decreasing northwest flow should carry a cool, slightly unstable air mass and snow showers to the Olympics and Cascades on Monday.

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.

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.

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

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 Sunday morning with a cooling trend but the next front is beginning to arrive on Sunday afternoon.

On Saturday morning the Hurricane rangers reported 25 inches of new snow on Saturday morning with strong south winds. In low visibility conditions they reported natural small 8-12 inch storm slab avalanches along the road near the ridge on the drive up although one was about 50 feet wide.

A great report was also received via the NWAC Observations tab for Saturday for the Hurricane area. In summary pit tests gave only a low quality shears or collapses and an ECT test that did not indicate any propagation. Loose dry avalanches were indicated as the main concern.

On Sunday morning the Hurricane rangers reported 7 inches of new snow. They reported that a snowboarder on Saturday triggered a small loose dry snow avalanche on the Sunrise run, a steep slope that faces northeast at about 5200 feet.

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.