SPRING AVALANCHE STATEMENT
Please note that regularly scheduled avalanche forecasts for the
past winter season have ended. However weather and snow
conditions will continue to be monitored at the Northwest Weather
and Avalanche Center with the information that remains available.
Additional forecasts will be issued when unusually severe
avalanche conditions develop. When issued such forecasts will be
available on the usual phone recordings and on the NWAC Web site.
If you have any comments or suggestions regarding this winter's
mountain weather or backcountry avalanche forecasting program,
please direct them to:
Northwest Weather & Avalanche Center
7600 Sandpoint Way NE
Seattle, Washington 98115
You may email comments to:
or phone 206-526-4666 and leave a message.
Please note that in areas retaining a significant winter
snowpack, backcountry travelers face a continuing risk of
avalanches during the springtime. We strongly advise that
backcountry travelers continue to assess snowpack stability as
they travel and project the effects of anticipated future weather
on the snowpack when making route choices.
Some general notes regarding spring avalanches follow . . .
During fair spring weather the avalanche hazard is generally
lowest during the night and early morning hours when surface snow
refreezes due to heat loss to the surrounding atmosphere. During
the day, intense solar radiation and warm air temperatures can
rapidly melt and weaken surface snow layers and produce an
increasing avalanche danger during the late morning and
afternoon. Wet loose slide activity generally starts on east and
southeast facing slopes receiving morning sunshine and progresses
to west and southwest facing slopes during the afternoon.
Therefore the safest time to cross potential avalanche terrain is
during early morning hours before the surface snow begins to warm
This daily melt-freeze cycle is strongly affected by any cloud
cover during the night since clouds at night limit radiational
cooling and prevent freezing. This may allow melt water and
associated snowpack weakening to affect progressively deeper
layers in the snow cover. Snowpack weakening is maximized when
warm days are followed by warm overnight temperatures and
overcast skies. Backcountry travelers should exercise particular
caution under these conditions that often lead to considerable
wet loose slide activity along with possible wet slab avalanches.
Backcountry travelers should also be aware that spring storms
might quickly produce unstable snow conditions. Although
precipitation may fall as rain at lower elevations, substantial
amounts of new snow may be deposited at higher elevations. This
new snow may form a poor bond with an old crusted snow surface.
Rapid rises in temperature following the storm due to intense
solar radiation may quickly warm and weaken recent snow, which
may need little or no disturbance to slide. While subsequent wet
loose slides may start small, they may entrain considerable snow
as they descend and may trigger larger wet slab slides as well.
Dangerous conditions may also result from unstable cornices
deposited by spring storms, as these may be quite unstable and
release during later warm days. Also, slopes beneath glide
cracks should normally be avoided, especially during the heat of
the day, as the entire snow cover may release from melt water
lubrication and weakening.
Precipitation as rain may also create unstable snow conditions.
This is because rain falling on an already wet snowpack causes
water to quickly percolate through the snowpack, which weakens
progressively deeper snow layers. If the water encounters a
crust or an ice lens, it may flow along this layer and lubricate
it, making avalanches increasingly likely within the snow above.
No matter what the season, backcountry travelers should avoid
slopes of questionable snowpack stability. Remember that many
areas, which undergo regular avalanche control during the winter,
may not be controlled in the spring.
Also remember that small avalanches may be dangerous, for
although wet loose snow in motion may be soft, when it stops
rapid hardening takes place. Most avalanche victims trigger the
avalanches in which they are caught, and almost half of all
avalanche deaths occur in slides traveling less than 300 feet;
with some slide fatalities occurring with victims buried only a
few inches under the snow surface. During past springs in the
Northwest, several fatal accidents have occurred from climbers or
skiers releasing and being caught in relatively small avalanches,
which subsequently carried the victims into or over a terrain
trap. Hence, backcountry travelers should be aware of both the
terrain above and below intended routes.
provided courtesy of the Northwest Avalanche Center