This sequence of several cyclones following each other is fairly common. As the initial
cyclone weakens, the trailing (western) portion of its cold front will become stationary.
This stationary front is a region of strong temperature gradients. The appearance of the
next upper air wave and jet streak is often sufficient to start the cyclone formation
process again.
figure 27f. GOES image, April 14, 0600 CDT
image courtesy of M. Ramamurt h y, University of Illinois, Urbana/Champaign