Extreme or high avalanche danger occurring or expected to occur within 24 hours: at least high danger in all three elevation bands.
Warning conditions expected within 12-48 hours. Forecasters expect the probability of a Watch to increase to Warning conditions in the majority of cases within the above timeframe.
Avalanche Special Advisory
Unusual conditions meriting special attention that does not meet Watch or Warning criteria, generally issued outside of the daily forecast season.
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.
Detailed Forecast for Wednesday:
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: firstname.lastname@example.org 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 surface snow refreezes due to heat loss to the surrounding atmosphere. During the day, sun effects 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 avalanche activity generally starts on east and southeast facing slopes receiving morning sunshine and progresses to the 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 and weaken.
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!
The Aspect/Elevation diagram describes the spatial pattern of the Avalanche Concern by aspect (the direction a slope faces) and elevation band (Above, Near, or Below Treeline). The diagram will be filled with black where the Avalanche Concern may exist. You can view the diagram as you would a mountain on a topographic map. The outer ring represents the Below Treeline elevation band, middle ring Near Treeline, and the inner ring Above Treeline. The diagram is oriented like a compass, with the top wedges representing north aspects, the left wedges representing west, etc.
Likelihood is a description of the chance of encountering a particular Avalanche Concern. It combines the spatial distribution of the Concern and the sensitivity or ease of triggering an avalanche. The spatial distribution indicates how likely you are to encounter the Concern in the highlighted avalanche terrain. The sensitivity indicates how easy it is to trigger avalanches including both natural and human triggered avalanches.
Size is based on the destructive potential of avalanches.
SMALL avalanches are relatively harmless to people unless they push you into a terrain trap.
LARGE avalanches could bury, injure or kill a person.
VERY LARGE avalanches could bury cars, destroy a house, or break trees.
HISTORIC avalanches are even more destructive, and nearing the maximum size the slope could produce.
Detailed Forecast for Wednesday: