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Snoqualmie Pass

Avalanche Special Advisory i

Issued: Thu, April 17, 2014 at 6:00 PM
Expires: Fri, April 18, 2014 at 6:00 PM

Issued: 6:00 PM Thursday, April 17, 2014
by Kenny Kramer

Please note that regularly scheduled mountain weather and avalanche forecasts for the past winter season have ended.  However weather and snow conditions will continue to be monitored at the Northwest Avalanche Center with the information that remains available.  Additional forecasts or special statements will be issued according to the criteria and schedule given here.

A mix of increasing winter and spring avalanche conditions should be seen in the above treeline zone especially in the Washington Cascades near and west of the crest and the Mt Hood area on Friday.

Avalanche Concerns

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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Storm Slabsi

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

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Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

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Snowpack Analysis:

A warm front spread increasing light precipitation over the region late Wednesday with a cold frontal passage moving through the region late Thursday.  As of Thursday morning, areas above 5000 feet had received about 4-8 inches of snow with less along the east slopes and at Hurricane Ridge.  Daytime warming and slightly rising freezing levels Thursday has pushed snow lines above 5500 feet and closer to 6000 feet.  This has wet recent snow and added some shallow additional new wet snow above tree line, mainly near and west of the Cascade crest.

Overall, this should not create a significant increase in the current avalanche danger, however, areas of new wind or storm slab may have built by late Thursday, mainly at the highest elevations above tree line. 

Rain or much less new snow is expected in areas such as Hurricane, near and below treeline in the Washington Cascades near and west of the crest, east of the crest and at Mt Hood, where some shallow wet snow conditions should be expected.

Detailed Forecast for Friday:

A cold front should move east of the region Thursday night.  This should cause a change to showers overnight with lowering freezing levels.  Showers should diminish or end by early Friday along with further cooling.  Cool temperatures and gradually clearing skies are expected Friday.   Only a few additional inches of snow are expected Thursday night through early Friday.  

This should mainly affect lee slopes above treeline where stronger winds and new snow should build some shallow wind slab conditions, mainly NE through SE facing slopes. Watch for signs of firmer wind transported snow or cracking snow.

The sun continues to get stronger as we get further into spring. Even with mostly cloudy conditions Friday, the sun could do its work mainly on solar slopes in areas where there is more than a few inches of recent snowfall. Wet loose avalanches are possible on such slopes, mainly above treeline in the Washington Cascades near and west of the crest and the Mt Hood area but may extend down into the near treeline zone as well. Watch for increasing pinwheels and natural or triggered wet loose avalanches that increase in size or extent during the daylight hours.

Rain or much less new snow should continue in the near and below treeline areas through early Friday, especially east of the crest. Less change in snow and avalanche conditions should be seen in those areas.

Note that the NWAC will issue a complete mountain weather forecast Friday afternoon and again Saturday as well as complete avalanche forecasts valid for Saturday and Sunday.