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Avalanche Forecast

Archived

Dec 1st, 2016–Dec 2nd, 2016

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

Olympics.

New shallow wind and storm slab layers are possible at Hurricane on Friday due to winds, some new snow and a warming trend.

Detailed Forecast

A frontal system will cross the Northwest on Friday. This will cause increasing southwest to west alpine winds, increasing rain or snow and a rise in snow levels.

Less new snow is expected at Hurricane than along the Cascade west slopes. But several inches of new snow seems likely from the upper part of the below tree line band to above treeline on Friday with a warming trend.

This weather may build shallow new upside down wind slab on lee slopes at Hurricane which should be mainly southeast to northwest slopes near and above treeline. Watch for firm wind transported or hollow sounding snow.

New shallow storm slab is also possible in areas that see rapid accumulations of new snow. The warming trend will also aid in the development of new upside down storm slab.

In most of the lower part of the below treeline band there is still insufficient snow for avalanches but watch for early season hazards such as terrain traps, rocks and creeks.

Snowpack Discussion

About 4 inches accumulated Monday at Hurricane Ridge area with generally light WNW winds recorded at the NWAC weather station.

Tuesday was a break between weather systems.

Another front passed over the Northwest on Wednesday. It has been a bit difficult to tell how much snow there was at Hurricane but the NWAC station there had about .9 inches of water ending on Thursday morning which would indicate about 9 inches. Winds on Wednesday were initially moderate southerly, shifting to more westerly and diminishing greatly by afternoon.

A bit of a break has been seen on Thursday.

A nice report was received via the NWAC website (Observations tab) for last Saturday in the Hurricane Ridge 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.

NWAC pro observer Matt Schonwald visited Hurricane on Thursday and reported lots of wind effects but a generally well bonded snow pack and snow profiles in pits that lacked a slab structure. The snow was found to be unconsolidated at lower elevations making terrain traps and creek crossings a hazard.

 

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.