For those who were not listening Monday and Tuesday Mornings between 5 am and 8:30 am to hear us talk about the high winds from the gravity wave here is a more detailed discussion and some links. There are many types of gravity waves in natural physics and many types in weather, most go unnoticed. In fact we've had this type of wind in Atlanta before, but never this intense. The grade school/high school explanation: the big complex of rain and thunderstorms pushed up a lot of air, it then fell back to earth, this caused a rapid change in temp and air pressure over a short distance putting the atmosphere out of balance, the wind accelerated as nature tried to get the atmosphere back in balance or equilibrium. A small mountain of air (high) was followed by a hole in the air (low). The wind rushed from the mountain to fill the hole. The steeper the grade or gradient between the two the harder the climb or the harder the wind. Nature trys to equal out the two to reach a flat known as a stasis. Ocean waves are another example. A rock dropped into a lake and the resulting splash and waves that radiate out from it are another example.

High school explanation: This small scale temperature/pressure/wind oscillation is called a wake depression or a wake low gravity wave, and was first researched in the 1970s and 80s by Dr. Ted Fujita of the University of Chicago.The thunderstorms and widespread rain that came through Monday morning was an MCC/QLCS mesoscale convective complex quasi-linear convective system. Stumpf el. al. (1991) concluded that the trailing stratiform rain shield of mesoscale convective systems can be dynamically significant by generating rapidly descending inflow jets at their back edges producing pronounced lower-tropospheric warming, intense surface pressure gradients and strong low-level winds. These MCC/MCS are like an inland hurricane without an eye and less round in shape. They are often the size of Missouri. This represents a huge amount of energy in the atmosphere and is enough to disturb even the large-scale atmosphere and jet stream. They typically develop a mesoscale rise-fall pressure couplet or mesohigh/mesolow coupling resulting in a mass momentum energy transfer flux equilibrium adjustment, which we simply notice as high winds. This is why the NWS had a  wind advisory in effect for the entire metro Atlanta area starting at 5 am Monday morning and we warned of potential problems with trees and power lines. But it was worse than expected. I would speculate this is because of the drought followed by all the rain making trees weaker and root zones soggy, and the fact that the strong winds came from the Southeast, an unusual direction for strong winds in this area, and thus one to which the trees are not acclimated. Gravity waves do not usually cause winds this high 40-60 mph. They can also cause sudden heat waves, initiate tornadoes, cause flight level air turbulence and various cloud formations. Many gravity waves are benign and most go bye unnoticed.

Here are some advanced links, but you can always google your weather questions anytime.

• Cross Section through Wake Low
• Gravity waves
• Wake low gravity wave research paper
• Wave dynamics
• More on wake low gravity wave
• See a gravity wave and tornado research