Posted by: pyeager | October 21, 2009

Second Severe Weather Season

Update: As of Thursday morning, the CPC had issued a tornado watch for eastern Texas and southwestern Louisiana, which is an indication that they were more concerned about severe weather than they had been on Wednesday, when this post was written.

We meteorologists define severe weather in a different way than most of the population. Meteorologists generally define severe weather as damaging thunderstorms and tornadoes while the rest of the population thinks of severe weather as any type of weather that is, well, severe. This, more logical, definition would include damaging thunderstorms and tornadoes but would also include damaging wind (not associated with thunderstorms), blizzards, floods, hurricanes, and so on.

We meteorologists define the weather seasons, though, so humor me while I speak from the meteorologist’s perspective today. Believe me, though; I agree with you when you think a hurricane should count as severe weather!

Severe Weather Season

Spring and the first part of summer is the time of year when dangerous thunderstorms and tornadoes are the biggest threat across the United States as the building heat and humidity of the growing warm season conflicts with the energy of the waning winter jet stream.

The frequency of intense thunderstorms diminishes during the summer and fall as the jet stream loses its punch, reducing the number of these meteorological battle zones.

Second Severe Weather Season

When the opposite occurs during the fall and early winter–the waxing energy from the jet stream as it begins to build toward winter conflicts with the remains of summer heat and humidity before it fades into winter–the meteorological conflict returns in the form of a “second severe weather season.” (By the way, the second severe weather season is something that will be in the Weird Weather chapter of my upcoming weather book, Weather Whys: Facts, Myths, and Oddities that will be published in March 2010).

Severe Weather This Week?

One of those potential conflict zones is setting up for Thursday and Thursday night across the United States in the area  highlighted area on the following Severe Prediction Center (SPC) outlook for Thursday/Thursday night:

SPC map indicating the risk of severe weather on October 22, 2009

SPC map indicating the risk of severe weather on October 22, 2009

A cold front will move through a warm, humid air mass (including some moisture from what was once Hurricane Rick in the eastern Pacific), producing a line of thunderstorms.

The SPC does not currently believe that the thunderstorms will reach a level that warrants the issuance of severe thunderstorm or tornado watches, but there is some potential for “severe” weather…and the weather pattern is an example of the second severe weather season.

–Paul Yeager


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