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Avalanche Forecast

Archived

Mar 16th, 2016–Mar 17th, 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 mixed bag of avalanche problems Thursday will keep heightened avalanche conditions in specific terrain. You can mitigate the loose wet and cornice risk by being aware of the terrain your connected with and by recognizing the rapidly increasing hazard in locations that warm quickly. Also, wind slabs may still be sensitive near and above treeline. 

Detailed Forecast

Sunshine and moderating temperatures should be the story on Thursday. However, cool easterly winds should help offset some of the warming trend Thursday.

Still, mid-March sunshine will affect solar slopes by increasing the likelihood of loose wet avalanches on steeper solar aspects by quickly breaking down sun or melt-freeze crusts. While most loose wet avalanches should be small, they will have the ability to entrain recent moist snow in specific terrain. Recently formed cornices have grown large and should become more sensitive with warming and sunshine. You can mitigate the loose wet and cornice risk by being aware of the terrain your connected with and by recognizing the rapidly increasing hazard in locations that warm quickly.

Lingering wind slab will mostly likely be found on NW-SE facing slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab instabilities. Treat wind-loaded slopes in higher terrain with caution Thursday.

Snowpack Discussion

Weather and Snowpack

Storms have moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels. Two deep surface low-pressure systems moved across the Olympic Peninsula last week with the first passing last Thursday, March 10th and the next on Sunday, March 13th. These systems caused very stormy weather.  

Cool and showery weather Monday and Tuesday with continuing moderate westerly winds deposited additional snow at lower snow levels. In the Hurricane Ridge area, about 2-3 feet or more of new snow has fallen since Thursday, March 10th. 

Periods of strong to very strong winds during recent storms created widespread wind and storm slab problems, creating dangerous avalanche conditions. These recent storms have also built large cornices along ridges.

Daytime warming and settlement have allowed storm snow weak layers to settle and stabilize, therefore, storm slabs have been removed from the avalanche problem list.

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 pro-observer Matt Schonwald toured around the Hurricane Ridge area Friday, March 11th. He found up to 20 cm of dense 1 F or P snow above the latest rain crust. Thin wind slab was generally not reactive except in isolated areas on N-NW lee aspects near treeline. Although cornices were large, they were generally firm and not sensitive. Windward slopes that had melted out a few weeks earlier had packed on a firm, and in places, icy thin cover. Overall Matt noted few current avalanche problems in the Hurricane Ridge area Friday, March 11th.

Recent storm snow instabilities should have settled out. The Olympics saw abundant sunshine for the first half of Wednesday which may have triggered a loose wet cycle on solar slopes before clouds increased in the afternoon. 

Hurricane Weather Station

Internet communications to the station have been disrupted at the NWAC office. We have identified the problem and anticipate the station to return online sometime soon; we have an open trouble ticket with our internet provider and remain hopeful we will be back online shortly.  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.