Avalanche Forecast

Archived

Jan 4th, 2016–Jan 5th, 2016

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Olympics.

Wind slab formed last weekend should be stubborn to trigger except in isolated areas, but continue to watch for these layers.

Detailed Forecast

The clear weather over the past few days has given way to increasing clouds and a return to a few light showers. More clouds and light snow showers are expected Monday.

While wind slabs formed last week may be much more stubborn to trigger, continue to watch and test for these layers, on a variety of exposures. Look for recently transported snow further downslope from ridgelines than you might expect.

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

Cool, mostly dry weather over the past few days with sunshine and mild afternoon temperatures have allowed for further snowpack settlement and created thin, sun or melt freeze surface crusts on exposed slopes. No field orbs have been received since last weekend.

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, however, surface snow conditions have changed due to the sunshine, warming and wind redistribution on many exposed slopes.

The wind slab that formed and observed 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.