Avalanche Forecast

Archived

Jan 3rd, 2017–Jan 4th, 2017

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 possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Further building or new wind slab should be the main avalanche problem on Wednesday. Be sure to read the forecast since wind slab may build on aspects where you don't expect it.

Detailed Forecast

Fair cold weather is generally expected to continue over the Olympics and Cascades on Wednesday.

But expect locally strong east winds to develop over the Olympics and Washington Cascades Tuesday night and Wednesday. Therefore new or further building wind slab should be the main avalanche problem on Wednesday. This new wind slab should be found mainly on NW to SE aspects on Wednesday especially at exposed location. There should be quite a bit of recent snow available for transport. Watch for firmer wind transported snow and remember that stiffer wind slab has the potential to propagate to larger avalanches.

Although NW to SE aspects will be indicated in the wind slab avalanche problem diagram remember to watch for firmer wind transported snow on all slope aspects or cross loaded slopes especially in areas with varied terrain and modified wind directions. Older wind slab may also linger on other slope aspects.

Snowpack Discussion

Weather and Snowpack

An Arctic air mass began moving into the Northwest Saturday night. This caused a change to cold north winds and upslope flow conditions along the north slopes of the Olympics where Hurricane had about 15 inches of new snow for the 2 days ending Monday morning.

Fair cold weather has been seen at Hurricane with N-NE winds the remainder of Monday and Tuesday.

Recent Observations

There were two triggered avalanches Friday in the Hurricane area, including a solo traveler who was partially buried after triggering a soft slab avalanche and was fortunately able to self rescue.

NWAC pro-observer, Matt Schonwald was back in the field in the Hurricane Ridge area Saturday, 12/31. Matt found evidence of widespread wind transported snow near ridges and cross loaded features, cornices on multiple ridges and evidence of naturally triggered storm slab avalanches, likely during recent storms late last week. In multiple test pits the 12/17 PWL was found still intact buried consistently 60-80 cm below the surface. However, strong, well settled snow above and good bonding is indicating that triggering this layer is becoming unlikely.

The NPS ranger on Monday reported loose dry avalanches along the road on Sunday. No further loose dry avalanches were seen along the road on Monday. Low visibility limited observations at the ridge on Monday.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.