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Winter Storm Severity Index

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The Winter Storm Severity Index was developed by the National Weather Service to convey potential societal impacts from winter storms.

It's a forecast tool and is beneficial to meteorologists before an event occurs. Not only is meteorological data important for creating the index, but urban areas, land use, and forest classification are just as important.

Here's a look at the Winter Storm Severity Index Scale. Impacts are ranked from none to extreme and take into account threats to life, property, and disruptions to daily activities.

There are six components that make up the Index. The Overall Component shows all six overlaid on a map of the United States. Those six components include: Snow Amount, Ice Accumulation, Flash Freeze, Blowing Snow, Ground Blizzard, and Snow Load.

Snow Amount helps meteorologists, emergency managers, and others prepare for transportation systems potentially impacted by the total amount of snow or the rate at which snow is falling. The use of climatology is important here because areas already accustomed to large amounts of snow would not have their life altered by these events.

Ice Accumulation takes into account the amount of ice and wind expected for a particular area. Large amounts of ice could cause widespread tree damage, transportation shut downs, and utility problems.

Flash Freeze looks at situations where temperatures quickly fall below freezing during or after precipitation. This would pose a threat to transportation systems.

The Blowing Snow component looks at how transportation could be affected by whiteout conditions or drifts. The National Weather Service states that it just takes 20 mph to move snow.

Ground Blizzards occur when snow that's already on the ground is combined with very strong winds. These will cause whiteout conditions and make travel very difficult.

Snow Load takes into account the weight of the snow that could cause damage to trees or power lines.

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Joie Bettenhausen


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