This paper investigates the connection of precipitation organization to the frequency distribution of precipitation intensity, including extremes. The organization of precipitating systems, for example isolated thunderstorms and mesoscale convective systems, is an expression of the influence of the large-scale environment on precipitation. A recent climatology of precipitation organization in the southeastern United States (Rickenbach et al., 2015, QJRMS) demonstrated that a simple framework of identifying the scale of precipitation organization from a radar precipitation dataset was able to capture important differences of the seasonal evolution in precipitation organization. The present study will focus on the question of whether the heaviest daily precipitation values are associated with isolated or mesoscale precipitation organization, and whether this association changes seasonally.

The analysis employs a four-year dataset of daily precipitation values across the southeastern United States to examine the association of heavy precipitation extremes with isolated versus mesoscale organization.  Daily precipitation data covering the four-year period 2009-2012 is derived from the National Mosaic and Multi-sensor Quantitative Precipitation Estimation (NMQ) radar-based dataset on a 1 km x 1 km grid that extends 100 km offshore (see Rickenbach et al. 2015 for details). Each pixel is associated with either mesoscale precipitation features (> 100 km in spatial scale) or isolated precipitation features (< 100 km in spatial scale). Preliminary results will be presented at the online conference.

Reference: Rickenbach, T. M., Nieto-Ferreira, R., Zarzar, C. and Nelson, B. (2015), A seasonal and diurnal climatology of precipitation organization in the southeastern United States. Q.J.R. Meteorol. Soc., 141: 1938–1956. doi:10.1002/qj.2500