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Avalanche Forecast

Archived

Mar 31st, 2016–Apr 1st, 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.

We are in the midst of the first extended spring warm up and avalanche cycle. The regional focus on Friday will continue on loose wet snow avalanches, cornice failures and glide avalanches. There is probably as much or more danger from loose wet avalanches in the lower terrain bands as the upper bands.

Detailed Forecast

Another day of light winds, sunny weather and very warm temperatures is expected in the Olympics and Cascades on Friday. Freezing levels will probably be near or above 10,000 feet. This means the regional focus will continue on loose wet snow, cornice failures and glide avalanches.

The regional cycle of extensive, potentially large natural or triggered loose wet avalanches is expected to continue on Friday. 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. There is probably as much or more danger from loose wet avalanches in the lower terrain bands as the upper bands.

Hurricane may still have large cornices along ridge-lines so avoid slopes below these overhead hazards. Unlike the loose wet problem you will likely not get advance 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.

The likelihood of triggering older wind slabs continues to diminish, but in isolated areas above treeline, a mix of old wind slab may still maintain an unlikely wind slab potential on a variety of previous lee slopes. Watch for cracking and firmer or chalky wind transported snow.

 

Snowpack Discussion

Weather and Snowpack

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

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

A large upper ridge and warm air mass is now over the Northwest causing light winds, sunny weather and the warmest temperatures by far so far this spring. Temperatures on Thursday are well into the 50's F at most NWAC sites and even the 60's F at some of the lower elevation sites on both sides of the Cascade crest.

The frequent March storms have built unusually large cornices along many ridges, some noted recently 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 recent storm snow at that time to be 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.