The precipitation efficiency (PE) of mesoscale convective systems (MCS) over Missouri during the summer of 2000 is examined in the context of flash flooding. Of the 10 individual MCS examined during 2000, only 4 were associated with rains that produced flash flooding. Of these 4 cases, two were associated with forward propagating MCS, and the remaining two were the outcome of regenerative MCS. PE factors are also evaluated for these events. While 3 of the cases were in the top 10 of the 20 individual 6-hour periods of PE evaluated, only one flash flood case was in the top 15 precipitable water measurements.

Also, two cases were examined, each with the lowest and highest PE values of the 10 MCS. Neither of these cases resulted in flash flooding. However, they revealed striking differences between the environments that engender high and low PE. In particular, the highest PE case might well be suspected of being a flash flood producer, without any further examination. With the lowest PE case, the MCS evolved north of a surface warm front, indicating elevated convection. The highest PE case resulted from a rapidly propagating squall-line type MCS. In the former case, relatively weak moisture supply and inflow decreased the ingested moisture and the resulting PE. In the latter case, the rapid forward motion of the MCS minimized the time that individual cells could exist over a given site, thus minimizing the rainfall totals at any given point.