Avalanche Forecast

Archived

Jan 2nd, 2016–Jan 3rd, 2016

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Olympics.

Heightened avalanche danger should be specific to steeper solar slopes where loose wet avalanches are possible. Wind slab formed last weekend should be unlikely to trigger except in isolated areas.

Detailed Forecast

The recent clear weather should give way to increasing clouds and a return to a few light showers, especially late Sunday at moderating temperatures.

A heightened avalanche danger should apply to wind-loaded slopes near and above treeline where east-southeast winds continue to build new wind slab on a variety of aspects. If you find the right (or better put, wrong) wind loaded slope, it will remain possible or even likely to trigger a small slab avalanche. Look for recently transported snow further downslope from ridgelines than you might expect.

Mild freezing levels should slowly lower during the day Saturday for the Olympics with light to moderate easterly winds forecast.

This weather should continue to allow the older wind slab to continue to slowly settle and stabilize. Wind slab will most likely be found on north to southeast aspects near and above tree line. Watch and test for inverted strong over weak storm snow.

Avoid venturing onto and below recent large cornices.

Snowpack Discussion

A cool very snowy storm cycle brought about 4 feet of snowfall to Hurricane the week ending December 24th. Light additional accumulations in the past week have allowed the snowpack to slowly settle with good skiing although recent warm temperatures and sunshine have formed crusts on solar aspects.

Wind slab formed last week should be much more difficult to trigger after a week of settlement.

The most recent observations were made Sunday the 27th by NWAC pro observer Matt Schonwald who found a wide distribution of wind slab along ridge features as well as cross loaded slopes below ridgeline. Matt ski cut a wind slab on a steep convex feature on a north facing slope at about 4800 feet. These features were evident on many exposed north to east facing slopes exposed to wind.

Hurricane Ridge December 27, 2015. Triggered wind slabs on a steep convex north slope, 4800 feet. Photos T. Allen

See the short video illustrating the stiffer wind slab over the weaker underlying snow:

Matt also reported that cornices were quite large overhanging some 2 meters in places and posed their own hazard due to their size. Unlike last year, there is now a healthy snowpack below treeline on all aspects.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.