Developing an MCS index using the climatology of South America

Abstract

Even though mesoscale convective systems (MCS) are of great importance in precipitation regimes besides being related to severe weather events, they are still not easy to predict. This study builds an objective index for South American MCS based on synoptic features present before the initiation of the MCS between 2005 and 2010. The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) product is used to access environmental conditions near the MCS-initiation centroid and in unorganized convective environments to obtain a South American MCS index (SA-MCS index). Upper and middle atmospheric levels presented the main patterns used to identify the MCS environments and unorganized convection, with the jet streak downstream of a short trough at medium levels frequently present in the convectively organized environment. The SA-MCS index is shown to depend on a vertical wind shear between 0 and 6 km high, temperature advection at 775 hPa, lifted index (LI) and vertical velocity omega at 800 hPa. When compared with the MCS index developed through the United States MCS climatology, the SA-MCS index was able to predict more than twice as many MCS at a distance of less than 1° from the point of maximum intensity of the index.