In mid-January 2014, the National Weather Service issued blizzard warnings for Montana and parts of the upper midwest on several occasions.
The Weather Service does not toss this phrase off casually: To be designated a blizzard, a storm must satisfy specific conditions, just as a tropical storm must have winds of 39 miles per hour or greater, and a closed low pressure center.
What is a Blizzard?
According to the National Weather Service, ‘blizzard’ means the following conditions prevail:
- There is sustained wind or frequent gusts of 35 miles per hour or greater.
- There is falling and/or blowing snow, frequently reducing visibility to less than one-quarter of a mile.
- The conditions must persist for a minimum of three hours.
The popular perception of a blizzard involves a large quantity of snow, but that is frequently not the case. This is especially true in connection with storms that move southeast out of Canada into the northern United States, particularly the northern plains. That particular area is so far removed from any source of moisture that snowfall is actually minimal in terms of water content.
Since these storm systems, sometimes called Alberta Clippers after their location of origin, are very cold, the snow associated with them is light, fluffy, and easily blown around. When it’s twenty degrees, a given quantity of water will produce twice the depth of snow that the same amount of water would produce at 32 degrees. This means that a storm with minimal moisture, if it is cold enough, will produce double the snow to blow in the air than it would if the temperature were warmer.
At any rate, the important factors in a blizzard are: duration; wind; reduced visibility. The total amount or water content or depth of snow is not relevant.
Where Do Blizzards Occur?
Heavy snowstorms with accumulations of over a foot in depth are common in the winter along the eastern seaboard of the United States. Yet blizzard warnings are rare in the area. For one thing, the wind doesn’t normally exceed 35 miles per hour, except along the coast where the wind off the warm water often turns the precipitation to rain. Furthermore, the snow is wet and heavy (temperatures are usually near freezing), and heavy snow doesn’t blow very much.
The northern plains, however, are the perfect location for blizzard conditions:
- The flat terrain allows the wind to reach blizzard-speed requirements.
- The cold temperatures allow the snow to be light and easily blown around.
- Alberta Clipper storm systems normally last for more than three hours.
What’s That Term?
Sometimes conditions are such that one is tempted to say the word ‘blizzard,’ but the wind isn’t quite 35 miles per hour, the visibility is a tad above a quarter of a mile, or the duration isn’t three hours. Still, it’s pretty bad and you need a term for it. What would one call these weather conditions without committing the faux-pas of using ‘blizzard’ incorrectly? The proper term is: blizzard-like conditions. Try it on your friends the next time it’s snowy and windy.© Copyright 2014 Jon Plotkin, All rights Reserved. Written For: Decoded Science