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Avalanche Forecast

Archived

Mar 18th, 2016–Mar 19th, 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.

Check the forecast for a mixed bag of spring avalanche problems and evaluate snow and terrain carefully on Saturday.

Detailed Forecast

Increasing mid and high clouds should be seen on Saturday. The best chance of some light rain or snow showers should be over the Olympics. Any rain and snow amounts will be light and should not cause a change in snow conditions.

The avalanche forecast won't change much from Friday.

Loose wet avalanches may still be possible on steeper solar aspects on Saturday. Loose wet avalanches may start small but could have the ability to entrain recent moist snow in mainly on steep solar terrain. High clouds Friday night may limit a refreeze of surface snow by Saturday morning.

Storm winds 3/13-15 likely built wind slab on lee aspects in the upper elevations of the above treeline band. This 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 layers.

Recently formed cornices have grown large and can become sensitive when it is warm and sunny. Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices in the spring.

Snowpack Discussion

Weather and Snowpack

Storms 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 3/10, and the next on Sunday, 3/13. These systems caused very stormy weather.  

Cool and showery weather Monday and Tuesday with prolonged westerly winds deposited additional snow at lower snow levels. In the Hurricane Ridge area, about 2-3 feet or more of new snow fell from about Thursday 3/10 to Tuesday 3/15. 

Periods of strong to very strong winds during recent storms are likely to have created wind and storm slab layers in the Olympics though current observations are lacking. 

These recent storms have also built large cornices along ridges with some recent releases.

Daytime warming and settlement should have allowed recent storm layers to gradually settle and mostly stabilize. Loose wet conditions or avalanches on solar slopes will have been likely by Wednesday and Thursday.

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 3/11. 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.

The Hurricane ranger did not see evidence of loose wet avalanches along the road on the drive up on Friday morning 3/18.

Hurricane Weather Station

Internet communications to the station have been disrupted at the NWAC office. We have a repair on-going with a technician and are hoping to 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.