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Avalanche Forecast

Archived

Mar 20th, 2016–Mar 21st, 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.

A mixture of typical spring avalanche problems exists with no one problem dominating. Evaluate the local snow and terrain carefully on Monday.

Detailed Forecast

Cooler temperatures, cloudy and showery weather is expected Monday.  This weather should maintain areas of wet and weak snow below about 4-5000 feet in the Below Treeline zone. Moderate to strong winds at the higher elevations should build new shallow wind slabs on some leeward exposed ridges, mainly NW-E facing.  Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Recently formed cornices have grown large and can become sensitive during mild weather, especially following nights with above freezing temperatures.  Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices in the spring. Cooler temperatures Monday may help temporarily strengthen cornices Monday.

Snowpack Discussion

Weather and Snowpack

A combination of sun and mild temperatures for several days gave way to mild temperatures and now light rain Sunday. The recent weather over the past five days has allowed for the 2-3 feet of storm snow that accumulated from about March 9-15 to settle and stabilize. Wind, sun, warmth, freezing and now rain have drastically changed snow conditions over the past several days. Surface snow conditions have become highly variable, ranging from some well settled old snow on steep shaded slopes and a mix of surface crusts, wind buffed surfaces or shallow wet snow on other aspects. Earlier formed avalanche problems of wind and storm slab have very likely settled and stabilized over the past several days of mild weather. 

The most recent storms did build large cornices along ridges with several releases noted over the past few days.

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

A Hurricane Ridge Park ranger found variable surface crusts Saturday morning, as overnight temperatures remained well over freezing. Similar conditions were found Sunday with the snowpack settling an additional 20 cm (8 inches) at Hurricane Ridge since Saturday morning, an additional sign of a strengthening snowpack.  

Hurricane Weather Station

Internet communications to the station have been disrupted at the NWAC office. The ISP inadvertently disconnected our service and we are anticipating the resumption of service, sometime Monday, March 21. We apologize for the outage and thank you for your patience.

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.

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.