A PV-streamer at 250 hPa, moving over the west central United States 25 June-5 July 1999 was visible on GOES-8 water vapor imagery as a narrow, elongated dark band. It sparked a series of mesoscale convective systems (MCSs) on successive days, producing heavy precipitation from Nebraska eastward and southeastward toward the coast along the Gulf of Mexico. The MCSs began as the PV-streamer moved off the central Rocky Mountains onto the Great Plains where it interacted with a surface front and a low-level jet. Each convective system interrupted the PV-streamer, and low- and mid-level vorticity accumulated along the front. One of the more spectacular MCSs that occurred 28 June 1999 is examined in detail. (C) 2001 Elsevier Science Ltd. All rights reserved.