The last daily NWAC forecasts for this season were issued on Saturday, April 11th. For the remainder of April, NWAC forecasts will be issued on April 17th, 18th, 24th and 25th to provide coverage those weekends. At any time this spring, blog posts and Special Avalanche Advisories will be issued if unusual or unusually severe avalanche conditions are expected.
NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.
SPRING AVALANCHE STATEMENT IN EFFECT
If you have any comments or suggestions regarding this winter's mountain weather or backcountry avalanche forecasting program, please direct them to:
Northwest Avalanche Center
7600 Sandpoint Way NE
Seattle, Washington 98115
You may also email comments to: email@example.com or phone 206-526-4666 and leave a message.
General notes regarding spring avalanches follow
During fair spring weather the avalanche danger is generally lowest during the night and early morning hours when
This daily melt-freeze cycle is strongly affected by any cloud cover during the night since clouds at night limit cooling and may prevent re-freezing. Lack of a thorough surface re-freeze may allow melt water to affect and weaken 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 avalanche conditions. Although precipitation may fall as rain at lower elevations, substantial 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 effects may quickly warm and weaken any recent snow, which may need little or no disturbance to slide. While subsequent wet loose slides may start small, they may entrain more snow as they descend and may trigger larger wet slab slides as well. Dangerous conditions may also result from cornices formed during spring storms; the cornices may become unstable and fail following warming. Slopes beneath glide cracks should normally be avoided as the entire snow cover may release from melt water lubrication and weakening. Glide avalanches are difficult to predict as they are not necessarily tied to the warmest part of the day or following the heaviest rain.
Rain may also increase the likelihood of avalanches. Rain falling on an already wet snowpack causes water to quickly percolate through the snowpack and weaken 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, are likely not controlled in the spring.
Also remember that small avalanches may be dangerous. Although the 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. Several fatal accidents have occurred during past springs 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.
Have a safe and enjoyable spring!