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Avalanche Forecast

Archived

Mar 12th, 2017–Mar 13th, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Olympics.

Mother Nature will throw a lot of serious avalanche problems at us again on Monday. The exact outcome of the snow, rain and warmer temperatures is hard to predict but we have to expect multiple types of potentially large or very large avalanches. Dangerous avalanche conditions are expected at Hurricane on Monday.

Detailed Forecast

A front should sag slowly south over the Northwest on Monday. Waves of moisture moving along the front should cause a very wet day in the Olympics and Cascades. Periods of moderate to heavy rain or snow should be heaviest in the Olympics through the morning hours with rising snow levels.

Mother Nature will throw a lot of serious avalanche problems at us again on Monday. The exact outcome of the snow, rain and warmer temperatures is hard to predict but we have to expect multiple types of potentially large or very large avalanches.

Loose wet avalanches are very likely in areas of intense wet snow or rain.

Avoid areas on ridges where there are potential cornices and slopes below cornices. Cornices will be weakened and prone to failure on Monday due to loading by wet snow and rain and warm temperatures.Large cornices have been reported from many areas and have been involved in recent accidents and close calls.

Wet slab avalanches are most likely in areas of intense rainfall where rain lubricates layers in the snowpack. Glide cracks can indicate areas where wet slab avalanches are likely.

Dangerous avalanche conditions are expected at Hurricane on Monday.

Snowpack Discussion

Weather and Snowpack

The first week or so of March was very cool and snowy. It looks like Hurricane had about 40-50 inches of snowfall.

A strong frontal system brought increasing precipitation and winds along with a warming trend to the Olympics and Cascades on Thursday. On Thursday night rain probably pushed up to about 5000 feet in the Olympics. By Friday morning Hurricane had about .5 inches of WE which looks like it fell as rain. This gave the snowpack a test and caused an avalanche cycle of several types of avalanches in the Olympics and Cascades.

Another front crossed the Olympics and Cascades on Saturday causing more SW-W winds, snow at higher elevations, and rain at low elevations. There was only up to a few inches new snow at Hurricane on Sunday morning.

Recent Observations

Reports by NPS rangers early Sunday 3/5 and a report listed on the NWAC Observations page indicates there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday 3/4, including the areas known as Maggies, Hurricane Hill and Sunrise Face.

The Hurricane rangers report that a snow boarder triggered a cornice release on Friday which in turn triggered a very large slab avalanche on the locally named Pit Bull path on a NE slope at about 5000 ft. A loose wet avalanche near the summit of Mt Angeles in turn triggered a large slab avalanche on S-SE slopes at about 6000 ft. Other loose wet avalanches from S-SE slopes crossed the main road below the level of Hurricane Ridge.

Goat Creek avalanche where it crossed the road at about 3500 ft. Photo by Dave Turner.

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.