A seasonal and diurnal climatology of precipitation organization in the southeastern United States

This article describes results from a new four‐year (2009–2012) radar‐based precipitation climatology for the southeastern United States (SE USA). The climatology shows that a size‐based classification between mesoscale precipitation features (MPF) and isolated precipitation reveals distinct seasonal and diurnal variability of precipitation. On average, from 70 to 90% of precipitation is associated with MPF, generally less in the summertime and in southern coastal regions. MPF precipitation has a relatively small seasonal cycle except in Florida and the warm offshore waters of the Gulf Stream. In contrast, isolated precipitation has a dramatic seasonal cycle that outlines the SE USA coastline whereas the MPF precipitation does not, consistent with a thermodynamic mechanism for onshore isolated storms in coastal regions. In summer, the isolated precipitation preferentially forms offshore at night, and dramatically ‘flips’ inland by early afternoon. In contrast, MPF precipitation has no clear diurnal variations except in the southern coastal region in the summer, likely associated with sea breeze convection organized on the mesoscale. These results suggest that the MPF versus isolated precipitation system framework provides a useful basis for future studies of large‐scale and local controls on precipitation and resulting implications for long‐range predictability of precipitation.