Just Blame it on the Jet Stream

By By Alex Sosnowski, expert senior meteoroogist.
June 20, 2011, 4:36:07 PM EDT

"...the polar jet stream has been much stronger and farther south, while the subtropical jet was very weak or at times non-existent."

Too cold, hot, wet, dry or stormy for you this spring? Blame it on the jet stream.

A persistent, strong jet stream over the U.S. and other areas has been responsible, in large part, for the north-south temperature extremes this spring.

While the jet stream is always there with its northward bulges and southward dips, it has been strong and persistent since early winter.

The jet stream is a fast river of air high in the atmosphere that marks the boundary between cool air to the north and warm air to the south. It is essentially the highway that storm systems travel on.

Typically, there are two main jet streams that circle the globe in the Northern Hemisphere; the polar jet farther north, and the subtropical jet farther south. Both divide cooler air from warmer air.


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The jet stream duo tends to fairly evenly disperse energy through the latitudes via the mechanism of storms, and moisture and temperature fluctuations.

However, during the La Nina that was so prevalent this winter and continued through May this spring, the polar jet stream had been much stronger and farther south, while the subtropical jet was very weak, or at times non-existent.

The single stronger, farther south polar jet stream resulted in extreme temperature patterns from north to south, and also helped to produce concentrated areas of precipitation and violent storms.

North of the jet, you were in the chill. South of the jet, you were in the warmth, and in some cases drought. Right under it, you were getting rifled with storm system after storm system.

The strong polar jet is believed to be a major contributor to the number and nature of tornadoes we had during April, May and early June.

There were other forces at work besides La Nina, and there are also other weather patterns that bring drought, flood, heat and cold, but it seems the cool tropical Pacific sea surface temperature anomaly was a big player this time.

While the La Nina has officially dissipated, its effects will continue to linger on the jet stream and cool/hot weather patterns over the U.S. and other areas well into summer.

Simply speaking, it will take some time for the over-revved ocean/atmosphere engine and its polar jet flywheel to slow down.


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