PLANET EARTH'S HOT SPOT

Latitude 30 degrees is the Earth's hot spot. The 30th parallel - north or south - is where global warming is being felt most and where where the Earth's drylands and deserts are found.

According to Dr. Kenneth Bowman, head of the Department of Atmospheric Studies at Texas A&M University Latitude 30 contains Africa's Kalahari, South America's Atacama, the barren regions of Australia, the Sahara, the sand-strewn Middle East as well as the Sonoran and Chihuahuan deserts of Mexico and the American Southwest.

However, southeastern United States is different than a lot of places of the same latitude, and while Houston averages 4.36 inches of rain in July, with an average high temperature of 93.6, Dallas, 240 miles to the north, is almost two degrees hotter with half as much rain.

The Dallas area sits at a natural weather divide, which roughly follows the Interstate 35 corridor from Laredo to Minneapolis.

On one side lies the forested east, where rainfall and evaporation balance out, on the other stands the drier west, a place of grasslands and shrubs on a mostly treeless plain.

But summer is dry in both halves of Texas because high pressure reigns.

That's because of the Bermuda high - a sprawling ridge of dry air often anchored in the Atlantic and stretching to Texas and beyond, Dr. Bowman said.

Because of it's high pressure it tends to be sinking air, which suppresses the convection that summer storms need.

The meteorological process is called a Hadley Cell: The equator's heat forces moist air to rise, and it spreads toward the poles because of Earth's rotation. The moisture falls as rain over the tropics, and the suddenly dry air begins to sink around the 30th parallels.

In the Texas summer, though, the effect of the Hadley Cell pushes farther north and takes the storm track with it.

Most summers don't see a cold frontal passage in July or August, as it's hard to fight that large-scale high pressure.

The western edge of the Bermuda high, which most affects Texas, can ebb and flow, allowing some storm fronts to slip through. But when high pressure drifts west and settles in, Texas temperatures soar.