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Avalanche Forecast

Archived

Apr 10th, 2015–Apr 11th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

Dangerous storm related avalanche hazards will generally be confined to the above treeline zone or in near treeline locations with enough of a snowpack to pose an avalanche threat. 

Detailed Forecast

A vigorous frontal system passing through Friday night will bring a sharp drop in snow levels by early Saturday morning.  Light and scattered post frontal showers Saturday morning should become more intense and widespread in the afternoon.  

Despite the strong cooling trend that will help new storm snow bond well to Friday night's snowfall, moderate and consistent westerly transport winds will continue to load lee aspects near and above treeline throughout the day.

Also, periods of intense snowfall during heavier showers combined with subtle daytime warming may locally escalate the storm slab potential Saturday afternoon and evening, with storm slabs failing within the new snow or new graupel layers.

Even with the winter-like temperatures, mid-April sunbreaks in the late morning or mid-day can trigger loose wet avalanches involving the new storm snow on solar aspects.  

Storm related avalanche hazards will mainly be confined to the above treeline zone or in near treeline locations with enough of a snowpack to pose an avalanche threat. 

Snowpack Discussion

A broad upper trough moved over the Northwest last weekend through early this week causing periods of light snow for the Olympics at low snow levels although only very minor new snowfall accumulated near Hurricane Ridge. On Wednesday and Thursday, clear skies transitioned to scattered afternoon showers with light and spotty new accumulations. April freezing levels have been very low compared to most of the winter, averaging about 4-5000 feet thus far.  A frontal system began to impact the Olympics Friday afternoon with wet snow seen accumulating on the Hurricane Ridge webcam. 

Unfortunately, we are still a long way off from building a meaningful snowpack in the Olympic mountains as we head further into spring.   

No recent snowpack observations have been received from the Olympics and most areas near and below treeline in the Olympics do not have enough snow to cause an avalanche danger.

Problems

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.

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.