Avalanche Forecast

Archived

Apr 4th, 2017–Apr 5th, 2017

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Olympics.

Difficult and dangerous travel and avalanche conditions will develop in the back country on Wednesday where careful snow pack evaluation and cautious terrain choices will be essential.

Detailed Forecast

Heads up because winter isn't done yet and the quiet weather and snowpack seen the past couple days is going to see significant snow and rain depending on location on Wednesday!

A front will stall over the Northwest on Wednesday with a series of waves moving south to north along the front. This should cause periods of moderate to heavy rain or snow on the Washington volcanoes especially Mt Baker with light to moderate rain or snow in most other areas. Precipitation should fall as snow in the above treeline and perhaps down into the near treeline zones.

New storm slab should build in the above and perhaps down into the near treeline in most areas and will be deepest where there is the most new, rapidly accumulating new snowfall. New storm slab should be very touchy especially if there is a daytime warning trend.

Loose wet avalanches should be seen in all areas in the near and below treeline. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger.

Recent cornices are very large and will get new loads on Wednesday. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

New wind slabs won't be added to the lengthy list of avalanche problems on Wednesday but should also build in the above and perhaps down into the near treeline in most areas. New wind slab should also be very touchy especially if there is a daytime warning trend.

Snowpack Discussion

Weather and Snowpack

Several inches of rain fell in the Olympics and Cascades on Friday, 3/17 to Saturday 3/18. Rapid cooling following the event formed a very strong crust layer, now buried by snowfall in late March.

The dominant wind pattern for the last several frontal systems at Hurricane have been moderate sustained S-SE winds. This transported snow to build fresh wind slabs in the Hurricane Ridge area.

Daily early spring warming temperatures in late March have allowed surface snow melt and consolidation at Hurricane at nearly the same rate as snow accumulations which should generally indicate strong surface layers.

A weak front crossed the Northwest on Saturday morning, causing light rain at Hurricane. This was followed by an upper trough on that caused some light amounts of snow at much cooler temperatures on Sunday.

Fair but cool weather has been seen in the Olympics and Cascades Monday and Tuesday. Reports generally indicate strong surface or near surface crust layers and shallow recent snow.

Recent Observations

No recent observations from Hurricane.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.