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Avalanche Forecast

Archived

Apr 5th, 2016–Apr 6th, 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.

Significant warming and intense solar radiation Wednesday should increase the likelihood of heat related avalanche problems, especially cornice failures and shallow loose-wet avalanches on steep solar slopes.  Stabilizing shallow wind slab may linger in specific areas at higher elevations, mainly easterly facing. 

Detailed Forecast

Clearing and warming is expected overnight Tuesday through Wednesday.

Any wind slab deposits caused from the shallow snow received Monday, in combination with moderate westerly winds should have mostly stabilized by Wednesday. However, watch for signs of wind slab on mainly easterly facing near and above treeline where extra caution is warranted.  Firm wind transported snow and snowpack cracking can be good signs of wind slab layers. 

Small loose wet avalanches, mainly involving any recent new storm snow from Monday and Monday night will be possible on any steeper solar slopes, especially during the warmest part of the day Wednesday afternoon. 

The likelihood of cornice failure will increase Wednesday from intense solar radiation and warming temperatures. Cornice releases can be unpredictable during the spring so continue to be aware of the overhead hazard and that cornices can break much further back than expected along ridges.

Snowpack Discussion

Weather and Snowpack

A large upper ridge dominated the weather last week through early Sunday, resulting in warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking midweek in the Olympic range. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last week.

A front moved across the Olympics early Monday morning, resulting in a period of mostly light precipitation, cooling and moderate westerly crest level winds.

A mostly cloudy day Tuesday with gradual warming has allowed for a generally decreasing danger as the shallow recent storm snow settles. 

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 observer, Matt Schonwald toured extensively in the Hurricane Ridge area Saturday, 4/2 and found a well settled and seasonally deep snowpack with very few avalanche concerns. 

During the warm stretch, 1 large glide avalanche (R3-D3) naturally released on the 20th of June slide path (easterly aspect, near treeline) to the ground. According to NPS rangers, the avalanche likely released on Wednesday or Thursday.  

Only shallow amounts of recent snow were received Monday through early Tuesday at Hurricane Ridge. This lead to a slight increase in danger, mainly on specific terrain features such as any exposed lee slopes at higher elevations that received greater wind deposited snow. 

Cloudy conditions and gradual warming by Tuesday afternoon is trending the danger downwards.

Problems

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.

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.