THE MAKING OF A WINTER STORM - WECT TV6-WECT.com:News, weather & sports Wilmington, NC

THE MAKING OF A WINTER STORM

In any part of the world, to create a winter storm (or any large-scale storm system) requires the coming together of a variety of elements at just the right time.  Not only that, but the amount and/or intensity of the given elements acts just as importantly as the timing of events.

One of the ingredients includes the proper positioning of the jet stream in the middle latitude regions of the United States.  Jet streams are the names of “rivers” of fast blowing winds in the upper atmosphere.  They are further defined by height of the stream above the surface of the earth, some being low-level jet stream speed maximums, some mid-level and some upper-level.  The lower-level streams are usually within 3,000 feet of the surface, and the upper-level streams from 18,000 feet and up.

 The proximity of a relatively warm air mass accompanied by plenty of moisture flowing up from the Gulf of Mexico and Atlantic are vitally important as well.  This, in conjunction with a sufficient amount of cold polar air flowing in from northern latitudes is also a minimum requirement, of course.  The polar air must be cold enough to drop temperatures below freezing through a significant layer of the atmosphere.

                Jet streams are a reflection of temperature gradients.  The more rapid the temperature changes horizontally and/or vertically through the atmosphere, the faster the winds blow and the more powerful the jet streams and associated storm system.  So, as warmer and colder air becomes aligned near one another, with sufficient moisture available as well, the more intense a storm will become. 

                Also in the upper atmosphere, there are areas of counterclockwise (cyclonic) spinning of air parcels.  Meteorologists call these “vorticity” centers, and the development of these is crucial for any storm to form.  There are numerous such vorticity centers circulating the globe at various levels in the atmosphere (including surface vorticities, for that matter).  The strength of these depends again on temperature gradients and resultant air mass density changes.  However, even with strong vorticities, sufficient rising motions must occur in conjunction with sufficient moisture to create precipitation.  Strong jet streams and associated vorticities pass without appreciable notice at times, given a dry and relatively stable air mass.

The major moisture sources for winter storms in the United States are the North Atlantic Ocean, the Pacific Ocean, and the Gulf of Mexico.  Much of the Pacific moisture is used up on the west coast and into the Rockies, so a plentiful supply of moisture must feed into a developing winter storm from the Gulf of Mexico, and eventually the Atlantic as the storm treks toward the coast, or re-forms as a Nor’easter and tracks up the eastern seaboard.

As you can see, the ingredients of a winter storm, in particular intense winter storms, are not all that easy to come by.  It takes a tremendous amount of atmospheric energy to generate these massive storm systems.  They do occur, of course, and if all comes together, heavy snow, ice, strong winds and severe wind chills result.  Not only that, strong winter storms also bring severe thunderstorms, some tornadoes, and flooding in the “warm sector” of the storm system.

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