The relationship between water vapor plumes and extreme rainfall events during the summer season

GOES 6.71-1m Water Vapor (WV) images were used to study the relationships beMeen the WV plumes and the upper and lower level circulation patterns related to extreme heavy rain-fall (125 mm or more in a 24-hour period) over the United States. The study covers three summer periods (May through Octo-ber, 1989-1991). One hundred and twenty nine cases were selected; 87 % were associated with a well defined WV plume. These WV plumes originated essentially in tropical ocean areas, such as the Paci:fic Ocean, Gulf of Mexico or the Caribbean Sea. As the plumes move northeastward into the United States, they are often aligned with low-level equivalent potential tem-perature ridge axes and upper-level forcing mechanisms (i.e., jet streams, short waves, and vortices). Occasionally these plumes ji'om the tropics interact with WV plumes originating from the polar regions or from the subtropics. These interac-tions often result in MCSs that produce flash floods. WV plumes associated with extreme heavy rainfall, were class!fied into fOllr categories. The categories were a fUll ction of the plume and jet stream structures. The present study shows that the WV plume appears to be one connecting link beMeen the global (climate) scale and the mesoscale/storm scale. 1