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Avalanche Forecast

Archived

Apr 19th, 2014–Apr 20th, 2014

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

Regions

Stevens Pass.

Increasing winter like avalanche conditions should be seen in the near and above treeline zone by late Saturday afternoon as a front moves across the region.

Detailed Forecast

An approaching Pacific front should move to the Washington coast Saturday morning, then spread increasing precipitation over the area Saturday afternoon and evening.  Freezing levels should rise ahead of the front, then lower with the onset of precipitation midday Saturday. 

Increasing snow with strengthening winds Saturday afternoon at lowering snow levels should begin to build new wind and storm slab layers.  Depending upon the how early the significant snow begins and the intensities, most areas should only see a modest rise in danger by afternoon.  However, if heavier snowfall begins earlier in the day Saturday, watch for a more significant increase in danger by Satuday afternoon, especially higher elevations. 

The greatest danger increase is expected on lee slopes near and above treeline on mainly north through east facing lee slopes. Watch for signs of firmer wind transported snow or cracking snow.

Snowpack Discussion

A warm front spread increasing light precipitation over the region late Wednesday with a cold frontal passage moving through the region late Thursday with showers persisting into early Friday.  As of Friday afternoon, areas above 5000 feet had received about 8-12 inches of snow.  

Daytime warming and slightly rising freezing levels Thursday has pushed snow lines above 5500 feet and closer to 6000 feet.  This wet recent snow and added some shallow additional new wet snow above tree line. Cooling overnight Thursday and early Friday allowed for a good bond to form on the old snow surface while adding some shallow, colder new snow amounts. 

The greatest recent storm snow has been received over the Mt Baker area where reports from Thursday and Friday indicated new storm and wind slab were responsive to ski cuts by ski patrol Friday morning and NWAC observer Jeff Hambleton also reported reactive new storm and wind slab while testing new snow conditions.

Storm slab releases on Mt Herman in the Mt Baker backcountry Thursday, April 17th. photo: Jeff Hambelton  

Recent storm slabs and wind slab should settle quickly given the warming daytime temperatures Friday, however they may be also susceptible to becoming wet and creating a wet snow 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.