What causes the "reverse monsoon" and extreme heat in the cross-timbers of Eastern Oklahoma and Western Arkansas? (climate, averages)

[bchris02]

If anybody knows this area, one of the primary characteristics of its climate is the extremely hot, dry summers. Its not uncommon to get little to almost no rain in the months of July and August in Eastern Oklahoma and Western Arkansas coupled with temperatures in the upper 110s. Its an ecosystem known as the cross-timbers, which consists of short, shrubby, drought resistant trees. Meteorologically, what causes this climate? Is it due to proximity to the desert southwest? The cross-timbers still get plenty of gulf moisture, which stops near the 100th meridian in western Oklahoma. Fort Smith, Arkansas averages over 40 inches of rain per year but almost none of it comes in July and August causing a cross-timbers climate. In addition, the temperatures in July and August are very comparable to what you find in the far Southwest, many times getting into the mid/high 110s. In 2011, Fort Smith, Arkansas hit 117 degrees. Personally, I think the cross-timbers are the least desirable region of the United States climate/ecosystem wise. No natural beauty whatsoever (the short, shrubby trees are ugly) and few redeeming characteristics about the climate. I prefer either a little farther west into the prairies or deserts or a little farther east into the humid subtropical region.