July 31, 2009

What's Wrong with the Weather?

"What's wrong with the weather" is a question that has been asked over and over again. The purpose here is not to get into a heated debate about long-term pattern change, but rather point out what has been going on this month and this summer in general.

This summer has had an extreme weather pattern of sorts. The jet stream is strong and well south, which has caused quite a bit of weather across the Central and Eastern states. It has also kept the heat out of the northern Plains, the Midwest and the Northeast. On the other hand, the same flow has produced a grueling heat wave in far western North America that recently has spread all the way to the Yukon.

The easiest way to understand this is to do an experiment with a long string or rope. Tie one end to a secure structure, stretch the rope out and hold on to the other end with your hand. Next rapidly flip your end of the rope up and down. The wavelength you generate is similar to the jet stream pattern. The jet stream would be the rope. How you change the speed of your hand will affect the ridges and troughs in the rope.

In summer, the ridges tend to bring hot, dry weather, while the troughs bring rainy, humid conditions. In between, invasions of cool, dry air take place.

The trough in the East and Plains has been tearing up the tropics, creating too much wind shear for tropical storms to form. The trough has also led to invasions of cool air in the Midwest and East. As this cool air has rammed into moisture from the Gulf of Mexico and the Atlantic, nasty episodes of showers and thunderstorms have occurred.

Farther west, the ridge has been producing above-normal heat in South Texas and the interior western U.S. and western Canada in general. A sharpening of this ridge in the past week has led to extreme heat in the Northwest and portions of western Canada.

What has been quite unusual this summer is the persistence of this pattern.
Typically, weather patterns come and go every few days. While some subtle changes will take place in coming weeks, no big differences in the pattern are likely in the short term. However, even subtle changes can have big consequences. Eventually though, this pattern will change like everything else.

AccuWeather.com Expert Senior Meteorologist John Kocet explained the atmosphere's effects on humans the best, "The atmosphere will continue to do what it wants. The problem is we often want something else out of a weather pattern."

Kocet added, "The way I see it, there are two choices. You can just accept it for what it is, or move somewhere else. However, once you move, the pattern will no doubt change, and you may be no better off than you were before."

Story by AccuWeather.com Expert Senior Meteorologist Alex Sosnowski

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