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Snoqualmie Pass

Avalanche Special Advisory i

Issued: Thu, April 24, 2014 at 9:36 PM

Issued: 9:36 PM Thursday, April 24, 2014
by Garth Ferber

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.

Corrected to add special banner on web site 930 pm Thursday.

Careful snowpack evaluation, cautious routefinding and conservative decisions should be essential near and west of the crest on Friday.

Avalanche Concerns

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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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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Snowpack Analysis:

It might be late April but Mother Nature hasn't been watching the calendar and weather systems have been causing heavy precipitation and heavy snow in the ATL and NTL zones near and west of the crest this week.

Water equivalents at NWAC stations near and west of the crest for the 3 days ending Friday morning will be in the 1.5-5 inch range with the most at Mt Hood. Snowfall for the same period at NWAC sites in the NTL zones near and west of the crest will be in the 1-2 foot range with the most at Paradise and Mt Hood which means wet heavy snow and more snow at higher elevations.

A couple of reports for today for near and west of the crest come from ski areas. The Alpental ski patrol reports a widespread natural avalanche cycle Wednesday night. Today in the ATL and NTL the Alpental and the Mt Hood Meadows patrols are reporting widespread easy ski triggered 8-12 inch large storm slab avalanches. Both are also reporting in the BTL widespread easy ski triggered large wet loose avalanches.

There will have been less precipitation and snow east of the crest but it may still be significant at higher elevations. The Washington Pass DOT crew this morning reported more winter like conditions and 6 inches of new snow and an extensive natural dry loose avalanche cycle with some small storm slab as well. Then local natural wet loose avalanches were seen on solar slopes today. At lower elevations further east of the crest where there has been less recent snow or rain there is getting to be some stable corn snow according to a report on TAY.

Detailed Forecast for Friday:

An upper trough will sink south over the US west coast on Friday. Light winds should be seen in the Olympics and Cascades and a few light showers should pop up near and west of the crest. Sunnier conditions are likely east of the crest. Overall snow levels will be fairly low and temperatures fairly cool for this time of year.

Some consolidation and stabilizing should decrease the avalanche danger from today to Friday.

But the recent new snow or wet snow will still be susceptible to spring solar effects and daytime warming on Friday. Watch for wet surface snow deeper than a few inches, natural or triggered snowballing, and small natural wet loose avalanches which usually precede larger avalanches on solar slopes. Wet loose avalanches will be listed likely near and west of the crest and possible east of the crest.

Local wind slab may last through Friday on cooler lee slopes. This should be mainly on north to east slopes in the ATL zone. Watch for signs of firmer wind transported snow or cracking snow. Wind slab will be listed in the ATL zones as possible near and west of the crest and unlikely east of the crest.

Storm slab was widespread today near and west of the crest but should mostly stabilize by Friday. It will be listed as unlikley in the ATL zone near and west of the crest. Storm slab is caused by temporary weak storm layers and heavy snowfall especially by warmer or denser snow.