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Avalanche Forecast

Archived

Mar 28th, 2016–Mar 29th, 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.

Light to moderate winds out of the northeast Monday night and Tuesday may redistribute recent snowfall to unusual aspects mainly above treeline. At lower elevations and in wind sheltered terrain, the main avalanche problem will shift from wind slab to loose wet due to sunny skies and warming temperatures.

Detailed Forecast

Light to moderate winds out of the northeast Monday night and Tuesday may redistribute recent snowfall to unusual aspects mainly above treeline. At lower elevations and in wind sheltered terrain, the main avalanche problem will shift from wind slab to loose wet due to sunny skies and warming temperatures.  

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. Moderate winds above treeline will limit the loose wet potential except on direct solar slopes. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences.  

A mix of older wind slab on lee easterly aspects and new wind slab on south through westerly aspects will make wind slab avalanches possible on a variety of aspects above treeline Tuesday. Watch for cracking and firmer or chalky wind transported snow. Yesterday's windward aspect may be today's loaded lee slope. 

Near treeline should be a mix of loose wet avalanche and wind slab concerns.  

Cornices have grown large recently in certain areas. 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 last Wednesday to Friday 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. 

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.  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.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.