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Distribution of mesoscale convective complex rainfall in the United States

TitleDistribution of mesoscale convective complex rainfall in the United States
Publication TypeManual Entry
AuthorsAshley, WS, TL Mote, PG Dixon, SL Trotter, EJ Powell, JD Durkee, and AJ Grundstein
Date Published{DEC}

{Several annual mesoscale convective complex (MCC) summaries have been compiled since Maddox strictly defined their criteria in 1980. These previous studies have largely been independent of each other and therefore have not established the extended spatial and temporal patterns associated with these large, quasi-circular, and, typically, severe convective systems. This deficiency is primarily due to the difficulty of archiving enough satellite imagery to accurately record each MCC based on Maddox's criteria. Consequently, this study utilizes results from each of the MCC summaries compiled between 1978 and 1999 for the United States in order to develop a more complete climatology, or description of long-term means and interannual variation, of these storms. Within the 22-yr period, MCC summaries were compiled for a total of 15 yr. These 15 yr of MCC data are employed to establish estimated tracks for all MCCs documented and, thereafter, are utilized to determine MCC populations on a monthly, seasonal, annual, and multiyear basis. Subsequent to developing an extended climatology of MCCs, the study ascertains the spatial and temporal patterns of MCC rainfall and determines the precipitation contributions made by MCCs over the central and eastern United States. Results indicate that during the warm season, significant portions of the Great Plains receive, on average, between 8% and 18% of their total precipitation from MCC rainfall. However, there is large yearly and even monthly variability in the location and frequency of MCC events that leads to highly variable precipitation contributions.}

Citation Key90
Community Notes

Study Findings:

  • Mesoscale Convective Systems (MCSs) are the source for significant amounts of precipitation over the Midwest during the growing season
  • MCCs are warm-season events
    • this study defines the warm season as May-August
    • the atmosphere is unstable due to greater heat and humidity and more large convective systems form
  • transitional seasons have more cyclone activity
  • there is great interannual variability in MCC frequency
  • from an agricultural perspective, convective precipitation is most critical for corn yields when moisture is at a premium
  • MCCs are frequent in the upper Midwest in June, and although there is a general decline in July for some regions, the upper Midwest continues to increase in frequency
  • August has significant drops in frequency
  • the anvil hour is defined as the number of hours MCC anvils are atop stations
  • In September, there are significant declines in MCC anvil hours and total MCCs
    • the anvil-hour core is located over northern Illinois, southern Lake Michigan, and northwest Indiana with a smaller core over northern Wisconsin