Issued: 7:31 PM PST Thursday, February 23, 2017
by Garth Ferber

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

Isolated lingering wind slab in the near and above treeline will continue to heal and become less sensitive to human triggering on Friday. You will need to watch for a wider variety of avalanche problems as we transition to spring. Continue to evaluate snow and terrain carefully on Friday.

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Avalanche Problems for Friday

Wind Slabi

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

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Snowpack Analysis:

Weather and Snowpack

The latest of several warm, wet SW streams of moisture this season arrived on Valentines Day 2/14 bringing another round of heavy rain, avalanches, crusts and consolidation through Thursday 2/16 in the Olympics and Cascades. Minor snow was seen at Hurricane Ridge at the tail end of the storm.

A short period of fair weather on Friday, 2/17 caused another surface crust, especially on solar aspects.

Light amounts of new snow accumulated over the weekend. The NPS rangers reported 5 inches of snow Monday morning at Hurricane Ridge. 

A mix of sun and light snow showers Tuesday to Thursday freshened the surface with a few inches of snow at cool temperatures and generally light winds.

Recent Observations

NWAC pro observer, Matt Schonwald traveled to the Hurricane Hill region Friday 2/17. A hard, slick surface crust made travel precarious early Friday before the sun and warming began softening the crust. The few inches of snow fell during the tail end of the storm had bonded well and filled in many rain runnels, helping to smooth surface conditions. There was little evidence that the latest rain event produced any avalanches. The main hazard in the Hurricane area appeared to be an uncontrolled fall on the slick crust.

A report via the NWAC Observations page for Hurricane for 2/18 indicates a sizable loose wet avalanche on the W-SW side of Steeple Rock that probably occurred during the 2/14-2/16 period.

Another report via the NWAC Observations page for Mt Ellinor gives locally more snowfall and touchy avalanche conditions on Sunday 2/19. 

Detailed Forecast for Friday:

A weak low pressure system should move north to south over the Northwest coastal waters on Friday. This should trigger light occasional moderate snow showers over the Olympics by Friday afternoon with light winds and low snow levels.

Lingering wind slabs should continue to heal, become isolated to specific terrain features, and become less sensitive to human triggering Friday. The most significant recent winds were generally S-W so NW-SE aspects in the near and especially above treeline will be indicated. Watch for signs of firmer wind transported snow.

Storm slabs are expected to have stabilized by this time.

Cloudier weather should limit the potential for loose wet avalanches on Friday and this will not be indicated as an avalanche problem. Watch for wet surface snow deeper than a few inches if you find yourself on sun exposed slopes during any extended sun breaks.

Loose dry avalanches will also not be indicated as an avalanche problem. You can do tests for loose dry avalanches by pushing snow onto small safe test slopes.

Avoid areas along ridges where there may be a cornice and slopes below cornices, since cornices can fail at any time.