Long-lived clusters of thunderstorms called mesoscale convective complexes , or MCCs for short, often produce low pressure areas in the middle levels of the troposphere that last long after the MCC has moved away or died. These circulations are called by several names, including convectively induced vorticity maxima, mesoscale vorticity centers (MVCs), or even "Neddy eddies" (after Ned Johnston, who was one of the first to observe and describe them). These types of lows, produced by thunderstorms, can profoundly influence weather hours or days later, even after moving hundreds of miles from where they form.

The color-enhanced radar image above, obtained from WSI, indicates the presence of an MVC. Note the curved, comma-shaped mass of rain (in green) over southwestern Oklahoma. This feature first formed near the TX/OK border in an MCC (the remains of which you can see in yellow to the east), and drifted eastward across OK for at least 6 hours. In radar time lapses, it had well-defined rotation.

This is a good example of how radar imagery, in this case a composite based on several WSR-88D (Doppler radar) units, can greatly assist in forecasting by revealing features that may escape computerized weather forecasting models because they're too small to be detected by widely spaced balloon observations.

[If you are interested in scientific references on MCCs or MVCs, please send me e-mail and I will direct you to some.]