AccuWeather.com

By Alex Sosnowski, Expert Senior Meteorologist

Apr 21, 2010; 8:10 AM ET

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A colder-than-average Gulf of Mexico is likely the main reason behind a much lower-than-average number of severe weather and tornado incidents so far this year in the U.S.

The relative quiet severe weather season thus far is positively impacting lives in Tornado Alley.

During this past winter, persistent cold air in the South chilled Gulf of Mexico waters to below-average levels. While the water is warming and the departures are decreasing, the water temperature continues to run lower than average.

Why Are Gulf Water Temperatures So Important?

The cold Gulf waters have been negatively impacting the supply of moisture to the middle and eastern parts of the U.S.

Cold Gulf water temperatures continue. Blue areas represent colder-than-average water temperatures. Image courtesy of the National Hurricane Center.

Meteorologists like to use the dew point temperature to get a feel for how moist and, hence, potentially unstable the atmosphere is. The dew point is the temperature to which the air must be cooled to become saturated.

If Gulf water temperatures are running several degrees below typical values, most likely dew point temperatures in the vicinity and downwind from the area will be lower than average as well.

The air flow in the spring and summer is often from the south or the Gulf of Mexico over the eastern two thirds of the nation.

The Cold, Hard Facts

Most severe thunderstorms (which spawn tornadoes) require high dew point air to form and survive. 60-degree dew points are marginal, while 70-degree dew points are better for severe weather development.

Over the eastern two-thirds of the nation so far this year, we have only had a handful of days with 60-degree dew points and we really have not had a day with widespread 70-degree dew points.

Actual number of cloud-to-ground lightning strikes through April 13, 2010. Data provided by Vaisala, Inc.

AccuWeather.com meteorologists believe the low dew points caused by the cold Gulf waters are the main player in the low count of thunderstorms and correspondingly lightning strikes, severe thunderstorms and tornadoes so far this year compared to recent years.

The team of meteorologists at AccuWeather.com also believe this ongoing trend will contribute to an eastward shift in the zone that experiences the greatest concentration of severe weather this season.

The number of tornadoes is lagging behind recent years, along with severe weather incidents and lightning strikes. Data by the National Oceanic and Atmospheric Administration.

Meteorologist and WeatherMatrix founder Jesse Ferrell offers some opinions and more facts about this year's severe weather season in his blog.

Risks of a Quiet Severe Weather Season

People need to be careful to not let their guard down.

As the warm weather season comes into full bloom, Gulf waters will warm sufficiently to allow high dew point air and lead to an increase in severe thunderstorms and tornadoes compared to recent weeks and months.

While we may never catch up to recent years in the overall number of severe weather and tornado incidents, one major outbreak or even a single tornado in a populated area could lead to tremendous loss of life and destruction.

Be sure to heed all watches and warnings. Experts at AccuWeather.com will let you know where the trouble spots are days in advance.

Case in point, AccuWeather.com meteorologists are monitoring the potential for a severe weather outbreak beginning over Texas and the southern Plains Thursday, shifting to the lower Mississippi Valley and the central Gulf Coast area by Saturday.

Related to the Story:

South Central Radar

Severe Weather Center

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