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Avalanche Forecast

Archived

Mar 30th, 2016–Mar 31st, 2016

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.

Warmth and the late March sun will focus the avalanche hazard on wet snow concerns Wednesday. High freezing levels, light winds and sunny skies over the next several days will cause natural loose wet avalanches on solar aspects and increase the odds for low likelihood/high consequence problems such as cornice failures.

Detailed Forecast

On Wednesday, freezing levels should rise to near or above 10000 feet in the Olympics. Warmth and the late March sun will focus the avalanche hazard on wet snow concerns Wednesday. High freezing levels, light winds and sunny skies over the next several days will cause natural loose wet avalanches on solar aspects and increase the odds for low likelihood/high consequence problems such as cornice failures.

Melt-freeze crusts can quickly break down with intense spring sunshine. In areas that have received more recent snowfall, small loose wet avalanches have the potential to entrain deeper layers. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences. Plan to avoid steep solar slopes by late morning/mid-day to minimize the problem.    

In isolated areas above treeline, a mix of older wind slab on lee easterly aspects and newer wind slab on south through westerly aspects will maintain wind slab potential on a variety of aspects. Watch for cracking and firmer or chalky wind transported snow.   

Many areas have large cornices along ridge-lines so be cognizant of the hazard above. Unlike the loose wet problem, you may not have much notice that a cornice is about to fail. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.

Snowpack Discussion

Weather and Snowpack

Snow accumulations Wednesday 3/23 to Friday 3/25 were about 4-6 inches at Hurricane with new snow of over a foot on wind loaded slopes near treeline. This snow bonded well to a moist crust buried March 22nd.

A strong front crossed the Northwest Sunday morning followed by a large upper trough and a cool unstable air mass Sunday afternoon and evening. Snowfall accumulations were lighter in the Olympics than the west slopes of the Cascades, with only a few inches of new snow likely through Sunday night. 

Hurricane Ridge pushed to 40 degrees early Tuesday afternoon under mostly sunny skies. 

Frequent March storms have built large cornices along some ridges in the Hurricane Ridge area.

The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC professional observer Matt Schonwald toured in the Hurricane Ridge area Friday 3/25.  Matt generally found the new storm snow unreactive in snowpit tests and with ski cuts on test slopes. No recent avalanches were observed in the Hurricane Ridge area. Wind effects were limited to directly below ridgelines, with generally settled powder and good skiing found on non-solar aspects with less wind effect. Area cornices were firm and unlikely to trigger.

The road to Hurricane Ridge was closed on Sunday. But the Park Service reported that hikers heard natural avalanches in the vicinity of Lake Angeles a few miles northeast of Hurricane. Details were not available due in part to low visibility.

Problems

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.

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.