You often see them marching across weather maps. Those blue and red lines with bumps and triangles are the fronts that bring changes in weather.

The blue lines with triangles are cold fronts, representing the leading edge of cooler air that can plow into warm air and lift it up like a snowplow lifts snow. The dramatic push upwards can create explosive thunderstorm development in spring and summer. The red lines with bumps are the warm fronts, indicating an invasion of warmer air riding up and over the cooler air below. This lift is more subtle and tends to create flatter stratus clouds that can produce large areas of steady rainfall.

These fronts are attached to low pressure centers that ride along the storm track, pushed and powered by the high-flying jet stream roaring overhead. But here in the middle of summer the jet stream is typically to our north, somewhere in southern Canada.

How do thunderstorms develop in the Midwest or southern Plains if the nearest cold front is hundreds of miles away? Meet the "air mass thunderstorm." These are storms that form using good old physics. Warm air rises and will keep going up as long as it is warmer than the surrounding air.

As the name implies, an air mass thunderstorm is a result of a warm, humid collection of atmosphere that can cover hundreds of miles. A moisture-laden, hot summer regime can extend from the Gulf of Mexico north to Wisconsin. The Earth's surface can be covered with dew points in the 60's or even 70's from New Orleans to La Crosse.

When the Sun heats the Earth, warm air rises up and carries the high dew point air along for the ride. Atmospheric pressure decreases with increasing altitude, so as the air rises it expands and that allows it to cool. Once it cools to the dew point temperature, moisture begins to condense and a cloud forms. Explosive clouds can evolve into huge thunderheads if the air aloft is significantly colder than the air at the surface.

A classic example of air mass thunderstorms occurs nearly everyday now in mid to late summer in the southwest United States. This is the summer monsoon in Arizona, New Mexico, Utah, Nevada and Colorado.

Dew points in the "desert" southwest reach above 55 degrees, which is high for that part of the world. The daytime heating causes this air to rise and huge afternoon and evening thunderstorms are the result. The summer monsoon rainfall provides many of the desert states with a majority of their annual precipitation, but it can also cause flooding because the heavy rain is falling on hard desert soil. That soil acts like concrete and the water runs off into ditches and culverts, filling them quickly.

Rain has been scarce around here lately, and the soil is getting hard and cracked in many locations. A good steady soaking rain would be nice, especially if it falls at night and doesn't ruin our outdoor summer daytime plans. Now if we could just control the weather ...

Watch Vince Condella on Fox 6 Sunday through Thursday at 5, 6 , 9 and 10 p.m. You can see the FOX 6 weather forecast around the clock at www.fox6milwaukee.com