Avalanche Forecast

Archived

Dec 28th, 2015–Dec 29th, 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

Olympics.

Wind slabs may still be sensitive to human triggering Tuesday. Remember MODERATE danger means human triggered avalanches are possible. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees. Also avoid recent large cornices.

Detailed Forecast

Partly to mostly cloudy, cool with light winds are expected Tuesday. This should allow for recent wind slabs to slowly settle and stabilize.

However, earlier formed wind slab will most likely be found on N-SE aspects near and above tree line and on some cross loaded features below tree line as well. Wind slab avalanches should stay within recent storm layers. Test for inverted strong over weak wind layers and give recently formed cornices a wide margin.

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

There have been snow immersion fatalities in tree wells already this season at Snoqualmie and in Canada. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees and maintain visual contact.

Snowpack Discussion

We have had about a week of heavy snow and cool temperatures in the Olympics and Cascades, with the snow tapering over the past three days with only a few inches each of the past two days reported at Hurricane Ridge. The Hurricane Ridge height of snow has remained at 87 inches Monday morning with just 1.5 inches new since Sunday morning. The storm snow over the past week has been about 4 feet at Hurricane Ridge. There has been some slow settlement over the last few days. The main message, other than it is deep, is the evidence of recent wind effects on many exposed slopes and terrain features.

On Sunday the 27th, NWAC observer, Matt Schonwald 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 N facing slope at about 4800 feet. These features were evident on many exposed N-E facing slopes exposed to wind.

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

Also reported that cornices were quite large, overhanging some 2 meters in places, and posed their own hazard due to their size.

In non-wind affected areas, the upper snowpack was generally right side up with increasing hardness with depth and still providing good skiing conditions. 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.