Mid-Latitude Cyclone over the United States

At 3:05 p.m. Eastern Daylight Time on September 26, 2011, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite observed a mid-latitude cyclone over the mid western United States. The center of the storm appeared immediately west of Lake Michigan.

Mid-latitude cyclones drive most of the stormy weather in the continental United States. Development of these cyclones often involves a warm front from the south meeting a cold front from the north. In the Northern Hemisphere, cyclones move in a counterclockwise direction. (In the Southern Hemisphere, cyclones are clockwise.) The bands of cold and warm air wrap around a center of low pressure, and air rising near the center spurs the development clouds and precipitation.

Justin Berk, a meteorologist based in Baltimore, explains that in this region, “cold air eventually wins out and wraps completely around a storm. This is called a ‘cold core’ storm and has cut itself off from the main flow of the jet stream.” This, says Berk, is why the September 26 storm appears stalled near Chicago.