Summary Avalanche Forecast for Olympics and Washington Cascades
Northwest Weather and Avalanche Center Seattle Washington
1006 AM PST Thu Mar 11 2010
The NWAC program is administered by the USDA-Forest Service and operates out of the National Weather Service Forecast Office in Seattle. NWAC services are made possible by important collaboration and support from a variety of federal, state and private cooperators.
WAZ 513-518-519-019-042-501-502
Avalanche Forecast
OLYMPICS AND WASHINGTON CASCADES NEAR AND WEST OF THE CREST-
AVALANCHE WARNING FOR LATE THURSDAY THR0UGH FRIDAY MORNING
Thursday: Considerable avalanche danger above 5 to 6000 feet and moderate below increasing Thursday morning and becoming high above 4 to 5000 feet and considerable below Thursday afternoon.
Thursday night and Friday: Further increasing avalanche danger becoming briefly high below 7000 feet Friday morning. Slowly decreasing danger expected Friday afternoon and night.
Saturday outlook: Considerable avalanche danger above 4 to 5000 feet and moderate below slowly decreasing
EAST SLOPES WASHINGTON CASCADES-
Thursday: Moderate avalanche danger above 5 to 6000 feet and low below increasing Thursday morning and becoming high above 6000 feet and considerable below Thursday afternoon.
Thursday night and Friday: Further increasing avalanche danger becoming briefly high above 5000 feet and considerable below Friday morning. Slowly decreasing danger expected Friday afternoon and night.
Saturday outlook: Considerable avalanche danger above 5 to 6000 feet and moderate below slowly decreasing
Snowpack Synopsis
Increasing amounts of wind driven snow at gradually rising freezing levels have been deposited over a variety of buried weak layers early to mid Thursday morning. These weak layers include low density snow, spotty surface hoar, and a slightly faceting old crust. This is producing a significant danger increase as slowly thickening and increasingly sensitive wind slabs gradually spread to lower elevations, especially on northwest through northeast exposures.
Thursday
A strong front is spreading increasing moderate rain or snow over most areas Thursday morning, along with increasing ridgetop winds and slight warming. This should be followed by periods of moderate to occasionally heavy rain or snow and continued strong winds Thursday afternoon along with further slight warming. With a variety of buried weak layers already in place, a resulting substantial increase in the avalanche danger is expected, with dangerous avalanche conditions developing on most lee slopes. Careful snowpack evaluation, cautious routefinding and conservative decsion making should become increasingly essential on Thursday in order to avoid avalanche involvement.
Thursday night and Friday morning
After the first front stalls and weakens over central WA late Thursday, a second frontal wave should spread further moderate to heavy rain or snow northward late Thursday night and Friday morning, along with further slight warming and another surge of strong winds. This weather should produce generally high avalanche danger in many areas, with natural and human triggered avalanches increasingly likely on steeper lee slopes. As a result, back country travel in avalanche terrain is not recommended. Safest travel shoulod be on windward ridges or lower angle terrain without steeper terrain above.
Friday afternoon through Saturday night
Moderate to heavy rain or snow should decrease and become mostly light to occasionally moderate snow showers Friday afternoon through Saturday morning along with gradually decreasing winds and substantial cooling. While this should allow for a slow decrease in the danger, especially at lower elevations, expected cold temperatures and continued wind transport should allow for only a slight decrease in the danger on lee slopes near higher ridgelines.
With the exception of a local slight increase in the danger on south facing slopes receiving sun breaks Saturday afternoon, scattered light showers, partial clearing and further diminishing winds should allow for a further slow decrease in the danger on more shaded lee slopes Saturday afternoon and night.
NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at www.nwac.us. Remember that these avalanche forecasts apply to back country avalanche terrain below 7000 feet outside of developed and operating ski areas or highways.
The NWAC program is administered by the USDA-Forest Service. NWAC forecasts, data and avalanche or mountain weather information are made possible by partnerships between the Forest Service and many important cooperators, including the National Weather Service, Washington State Department of Transportation, Washington State Parks and Recreation Commission, Washington Snowparks and Snowmobile Grants, National Park Service, Ski Washington, Pacific Northwest Ski Area Association, the Friends of the Avalanche Center and others.
This forecast is prepared for cooperators and users of the NWAC, as an aide to tranportation and recreational operations, and to help promote public safety in the NW mountains.
Moore/Northwest Weather and Avalanche Center Seattle Washington