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Avalanche Forecast

Archived

Mar 18th, 2014–Mar 19th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Expect increasing avalanche danger on Wednesday as a front moves over the area.  Watch for loose wet concerns in the morning and shallow but sensitive wind and storm slab in the afternoon. 

Detailed Forecast

A quick moving but powerful frontal system should blow through the Olympics in the late morning to mid-day on Wednesday, with a strong cooling trend in the afternoon during post frontal showers. 

Rain at lower elevations should allow for wet-loose concerns in the AM.  While there is a favorable temperature trend with this storm watch for new storm instabilities during times of intense precipitation and expect fresh wind loading on lee slopes near and above treeline. 

Take note on how the new storm snow bonds to the previous snow surface and watch for cracking on lower angled terrain as a sign of new storm snow instabilities. 

Snowpack Discussion

A stalled and moist frontal boundary draped over mainly the north WA Cascades Saturday afternoon finally sagged south on Sunday, with rain changing to snow generally in a north to south fashion across the PNW mountains. A favorable temperature trend occurred with this storm, with gradual cooling from Saturday night through Sunday night.  From Saturday night through Monday morning Hurricane Ridge telemetry and NPS reports indicate about 18 inches of snow fell. Generally light showers at cool snow levels were seen through the day Monday, but moderate NW winds aloft likely transported snow Sunday night and continued into Monday in the alpine. 

Over the weekend NWAC observer Katy Reid reported a generally well consolidated lower snowpack near treeline with moist snow from last week's periods of rain and warm temperatures reaching down from the upper to mid snowpack.  A NPS park ranger at Hurricane Ridge reported a backcountry skier on Sunrise Ridge above the road Sunday afternoon was able to ski cut and release a storm slab about 15-20 ft wide that covered the uphill lane with debris. Fortunately the skier was not caught in the slide due to daytime warming creating unstable slab conditions.

Gradual warming on Tuesday and a break between significant precipitation has likely allowed the most recent storm and wind slabs to settle and the snowpack should be relatively ready for the next incoming frontal system on Wednesday. 

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.

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.

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.