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Avalanche Forecast

Archived

Feb 25th, 2016–Feb 26th, 2016

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

Regions

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Moderately high freezing levels and light amounts of rain or snow at slowly cooling temperatures should not cause a significant increase in danger Friday. Shallow areas of wet snow or isolated wind slabs should be the primary avalanche concern. 

Detailed Forecast

Increasing high clouds overnight Thursday should still allow for stabilizing surface crust formation by early Friday.

A weak front should allow for light rain and snow at moderate freezing levels later Friday afternoon. Only a light amount of precipitation is expected during the daylight hours and this should not cause a significant increase in the danger.  

Some shallow new wind slabs may form at higher elevations by late Friday on some lee slopes that receive greater precipitation.

Snowpack Discussion

Weather and Snowpack

Springlike weather under high pressure Wednesday and Thursday caused abundant sunshine with temperatures climbing into the upper 40's to mid 50's Thursday afternoon! 

This fair and mild weather has allowed for melt-freeze crust formation overnight and varying amounts of wet surface snow depending on slope aspect, during the warmest part of the day.

The last storm cycle  occurred late last week when about 1-3 feet of snow fell from the 17th-20th. Some cornices and wind slabs formed during this period, with many triggered wind slabs reported last weekend.

Strong E-SE crest level winds in many areas Monday night and Tuesday of this week, redistributed surface snow and built new localized wind slabs on more non-traditional west facing slopes. Some of these wind slabs were touchy earlier this week, but have stabilized quickly under the warm weather.  The image below highlights a 1-2 ft wind slab on west aspect near Pan Face above Paradise, Mt Rainier that released Wednesday afternoon, 2/24.

Wind slab formed from east winds, Tuesday, 2/23/16. Released Wednesday, 2/24/16. West aspect, crown 1-2ft, near Pan Face, Mt Rainier, ~7000ft elevation. Photo - Peter Ellis 

Last week, heavy rain and mild temperatures dominated along the west slopes forming the latest rain crust. NWAC sites in the near and below treeline recorded 2-6 inches of water mostly as rain over the 2 days ending Tuesday, February 16th.

The mid and lower snow pack along the west slopes should be a stable mix of crusts and layers of moist and rounded snow crystals.

Surface hoar has been growing on shaded slopes over the past few days and where not destroyed by sun or expected rain, could be a layer to watch for in the future.

Recent Observations

NWAC pro-observer Dallas Glass was in the Alpental Valley Thursday, 2/25 reporting strong early morning melt-freeze crust that quickly became increasing wet surface snow on solar aspects. No wind slabs were found with mainly an increasing threat of loose-wet avalanches as the warming continued.

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.