A five-year climatology of precipitation organization in the southeastern U.S: initial results

This paper presents preliminary results of a five-year climatology of precipitation system organization in the southeastern U.S. with a focus on North Carolina. The overarching premise of this NSF-funded study is that a climatology of precipitation system organization, referred to as “mode of delivery”, will lead to improved characterization of regional hydrology and will provide an unique tool for the process-based downscaling of climate simulations. “Mode of delivery” refers to the structural, temporal and water phase characteristics of a precipitation system. Examples of mode of delivery that occur in the southeastern U.S. include short duration and spatially heterogeneous convective cells, large mesoscale convective systems, widespread long-lasting frontal precipitation, tropical cyclones, and winter precipitation. The value-added information beyond simple rainrate is that each “mode of delivery” may produce similar time-averaged precipitation totals, but have very different climate and hydrological impacts due to different spatial and temporal distributions of precipitation. A climatology of the “mode of delivery” with respect to dominant synoptic regimes (e.g. sectors within extratropical cyclones, seasonal cyclone track patterns) can tie together the less predictable precipitation regimes to the more predictable dynamical regimes, to improve long-term regional precipitation forecasts.

For the period 2009-2013 we will present preliminary results of a pixel-based and spatial-average analysis of precipitation: frequency of occurrence, ice/liquid phase, organization, and precipitation event duration. The analysis is based on a portion (stitched tiles 7 and 8) of the NMQ Q2 three-dimensional radar reflectivity mosaic and QPE dataset. All near-surface rainfall features > 0.1 mm/hr are identified and segregated into size categories, which determine whether or not each is associated with a mesoscale convective system. Within these features, precipitation is flagged in the dataset as convective vs. stratiform, frozen vs. liquid precipitation, and shallow (warm) rain. The duration and frequency distributions of each precipitation type at each pixel is tracked and integrated over daily, weekly, and seasonal time periods over the five-year period.