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Avalanche Forecast

Archived

Dec 25th, 2015–Dec 26th, 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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A consolidating and stabilizing trend will continue on Saturday. Remember to discuss plans and maintain visual contact with your partners.

Detailed Forecast

An upper ridge will shift over the Northwest on Saturday. This should cause light winds and fair weather on Saturday with freezing levels staying low in the Olympics and Cascades. Some high clouds should be seen by Saturday afternoon from a weak system that will approach Saturday night.

This weather will bring further consolidating and further stabilizing on Saturday. Cool temperatures may somewhat slow the stabilizing but the avalanche danger will be less than the previous few days.

Recent wind slab should remain possible on north to east slopes in the above tree line east of the crest. Wind and storm slab avalanches should stay within recent storm layers but could still move fast. Test for inverted strong over weak storm snow and give cornices a wide margin.

Beware of loose dry avalanches in steep non-wind affected terrain that could have unintended consequences such as knocking you off your feet and into a terrain trap.

Remember to discuss plans and maintain visual contact with your partners.

Snowpack Discussion

We have had about a week of heavy snow and cool temperatures in the Olympics and Cascades. Sites east of the crest have had 2-4 FEET of snowfall during this time!

A report via the NWAC Observations page indicates 2 skiers were caught in a wind slab avalanche, carried a short distance but then were able to dig themselves out on Driveway Butte on Tuesday in the Methow River area. The crown at the trigger point was 6 inches but ranged up to 2 feet. This was on a north slope at about 5840 feet.

A snow pit report from 5700-6500 foot range in Stemilt Basin near Mission Ridge also on Tuesday indicated a buried surface hoar at 45 cm. This layer gave some cracking and whumping.

NWAC pro observer Tom Curtis was at Iron Mountain a bit west of Blewett Pass on Wednesday and found some wind slab on steep open slopes even to below tree line and often above terrain traps like creeks or trees. A storm layer was seen at 35 cm with wind and storm slabs reacting to tests to this interface. He noted wind slab releases of 20-35 cm on northeast to east slopes near tree line and storm slab releases near and below treeline on steep terrain features of varied aspect and on small steep slopes above Forest Service roads. He also found some difficult trail breaking in deep powder.

A report from the North Cascade Mountain guides near Washington Pass on Wednesday indicated a storm layer at 15-25 cm but ski cuts on test slopes did not give any results. Another report from the guides near Washington Pass on Thursday indicated a storm layer at 30 cm with isolated small ski triggered storm slab and some loose dry releases and good stability. A couple natural small wind and storm slab near ridges and dry loose avalanches were noted. Quite a bit of wind effect was seen on some nearby slopes. Natural cornices drops did not cause any avalanches.

The southeast zone should have a shallower snow pack. However, we have no recent observations from the southeast zone.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.