18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Wednesday, 1 August 2001: 5:15 PM
Mesoscale convective systems over the United States during 19992000
Christopher J. Anderson, Iowa State University, Ames, IA; and R. W. Arritt and L. Strehlow
Poster PDF (108.9 kB)
We have constructed a climatology of mesoscale convective systems (MCS) for 1999 and 2000 using the automated IR satellite image classification method originally developed by Augustine and colleagues. MCS are classified as MCC (the familiar quasi-circular systems), or as PECS (persistent elongated convective systems; these satisfy the MCC size and duration criteria but not the shape criterion).

Both 1999 and 2000 were active years for convective systems. MCCs during 1999 showed a rather typical spatial-temporal distribution through most of the warm season, with the most common initiation position progressing from south to north during the season. The effect of the North American monsoon system, which was unusually strong in 1999, is clearly apparent as a decrease and northward shift in both MCC and PECS distributions after monsoon onset. This response to the monsoon likely contributed to the late-summer drought over much of the central U.S. during 1999. During the warm season of 2000, systems were predominantly located north of 35 North latitude, consistent with a general northward shift of the jet stream. The effect of North American monsoon onset on seasonal evolution of MCC and PECS distributions was not as strongly apparent for 2000 as for 1999.

Analysis of the results is continuing and additional findings will be shown at the conference.

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