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Avalanche Forecast

Archived

Dec 30th, 2015–Dec 31st, 2015

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.

A MODERATE danger means human triggered avalanches are possible. Watch mainly for possible wind slab on north to southeast aspects and for possible loose wet avalanches on steep solar slopes. Avoid venturing onto and below recent large cornices.

Detailed Forecast

Sunny weather should be seen on Thursday. Warmer temperatures should be seen at higher elevations in the Olympics by Thursday afternoon.

This weather should allow 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.

The sunny weather and warmer temperatures at higher elevations should bring the possibility of loose wet avalanches Thursday afternoon on steep solar slopes. Watch for surface wet snow deeper than a few inches, initial roller balls and natural loose wet avalanches on steep solar slopes where snow may shed from rocks or cliffs.

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. A weak weather system Sunday and Monday helped create some new mostly small and mostly shallow wind slab in many areas 

The main message is that most of the storm layers have settled, leaving some areas of the recent wind slab as the primary avalanche problem on many exposed slopes and terrain features. 

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

Matt 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.

A report on Turns All Year for 3 of the past several days indicated good ski conditions with a sun crust forming on south 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.