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Avalanche Forecast

Archived

Dec 25th, 2015–Dec 26th, 2015

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

Stevens Pass.

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 will be most likely to linger on north to east slopes in the above tree line. 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. Recent unconsolidated storm snow is very deep in many places with possible very large tree wells. There have been snow immersion fatalities in tree wells already this season at Snoqualmie and in Canada.

Snowpack Discussion

We have had about a week of heavy snow and cool temperatures in the Olympics and Cascades. Sites near and west of the crest have had 5-9 FEET of snowfall during this time!

Recent pro back country or pro patrol observations indicate extensive avalanches but confined to recent storm snow.

NWAC pro observer Lee Lazzara was in the Canyon Creek area near Mt Baker on Wednesday in the 2000-5400 foot range and found a right side up upper snow pack but with new snow layers also building quickly and a weaker storm layer at 20 cm. He noted numerous small natural and triggered storm slab and loose dry avalanches mainly on west to north to east facing slopes.

The Baker pro patrol on found fairly extensive 6-8 inch storm slab on Thursday morning. A skier out of bounds on a northwest slope at 4500 feet also triggered a 6-8 inch storm slab and was buried except for a glove showing and was luckily dug out by his friends.

NWAC pro observer Dallas Glass was at East Peak near Crystal Mountain on Thursday and found an overall right side up snow pack. The low sun angle was causing little solar effects on the snow. Storm layers at about 30 and 45 cm were not significantly reactive with minimal propagation. He reported one small natural 12 inch storm slab on an east slope at 5800 feet that had released similarly on each of the previous couple days along with several small loose dry avalanches. He kicked a couple cornices onto test slopes without results.

A skier near the Mt Baker ski area on Thursday reported via the NWAC Observations page that ski tests on the southwest slopes of Mt Herman were giving 6 inch storm slab with good propagation including to nearby slopes.

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.