MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES 
AND MT HOOD AREA
NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON
500 PM PDT FRI JUN 19 2009

NWAC Program administered by:
USDA-Forest Service
with cooperative funding and support from:
Washington State Department of Transportation
National Weather Service
National Park Service
Washington State Parks and Recreation Commission
Pacific Northwest Ski Area Association
Friends of the Avalanche Center
and other private organizations.

This forecast is prepared primarily for federal, state and 
private snow safety programs in Washington and Northern 
Oregon.

WAZ513-518-519-019-042-501-502-ORZ011-210000-

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SUMMER AVALANCHE STATEMENT

Please note that the Northwest Weather and Avalanche Center is 
closed for the summer.  However, daily operation is scheduled 
to begin again in the fall.

Because avalanches continue to occur at higher elevations 
during the summer months in areas having either residual snow 
cover or permanent snow and ice cover, and several people 
within the Northwest have been killed by these events, here 
are a few notes about summer avalanches.

Avalanches occurring during the summertime can be generally 
grouped 
into three types:

First, wet slides within the existing snowpack are similar to 
wet spring slides, as progressive weakening occurs within the 
snowpack through melting and water percolation.  Although 
these slides are most likely to occur during the warmest part 
of the day, they may occur at anytime of the day during 
periods when the snowpack does not refreeze substantially at 
night.

The second type of summer avalanche occurrence is associated 
with new snowfall at high elevations.  Summer snowfalls are 
usually followed by substantial warming of the newly fallen 
snow as air temperatures rise rapidly with intense summer 
sunshine.  When the new snow overlies an old snow, ice or 
smooth rock surface this may lead to possible wet loose or wet 
slab avalanches.

The third type of summer avalanche is an ice or snow and ice 
avalanche.  These are usually triggered by the failure of 
large ice blocks such as seracs within glacier icefalls.  This 
in turn may involve additional ice and/or snow.  Timing of 
these events are mostly random, usually being associated with 
both meteorological conditions and glacier motion.  However, 
they are most likely to occur during extended periods of warm 
weather.

Climbers, hikers and other back-country travelers during the 
summer are advised to evaluate snow stability and use normal 
safety practices for travel in avalanche terrain with snow 
cover.

If you have any comments or suggestions regarding this past 
season's mountain weather or back-country avalanche 
forecasting program, please direct them to:

Northwest Weather and Avalanche Center
7600 Sandpoint Way NE
Seattle, WA  98115

You may email comments to:

nwac.sew@noaa.gov

Have a safe and enjoyable summer!

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.

Ferber/Northwest Weather and Avalanche Center

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