A typical forecast here at Channel 4 includes "H's" and "L's" depending on what is happening with the weather. Generally, an "H" for high pressure means fair weather, and an "L" means stormy weather. But, of course, that's not always the case. These highs and lows that we draw on the map refer to what is happening at the surface. For the past two weeks, the meterologists here have been spending a lot of time talking about a strong "ridge" of high pressure in the upper levels of the atmosphere. Take a look at this map from the upper levels of the atmosphere (about 18, 000 feet up).
You can see there is an "H' positioned over Tennessee, Georgia and North Carolina, and there is a line around the high drawn from Texas to the Great Lakes, out into the Atlantic, and then the line comes back across Florida and makes the circle complete in Mexico. This tells the meteorologists here that there is a strong high, or "ridge of high pressure" in the upper levels of the atmosphere over the southeastern states. This ridge allows warm, tropical air from the Gulf of Mexico and Caribbean Sea to stream into the United States. In this image, the warm, humid air finally meets up with colder, drier air near the Central Plain states of Kansas, Nebraska, Iowa, etc. (The area on the map where the lines are closer together indicating an area of strong winds-the jetstream.) Strong ridges of high pressure during the summertime can often lead to record breaking heat.

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