19th Conf. on weather Analysis and Forecasting/15th Conf. on Numerical Weather Prediction


Large–scale Environment and diurnal cycle of u.s. warm season precipitation episodes

D. A. Ahijevych, NCAR, Boulder, CO; and R. E. Carbone, C. A. Davis, and J. D. Tuttle

In the Central U.S., a large portion of the warm season precipitation falls within mesoscale convective systems, or MCSs. These MCSs often initiate in the lee of the Rocky Mountains and track eastward toward the Mississippi River Valley. When viewed in time-longitude space, it is not uncommon to find areas of precipitation which persist through one or more diurnal cycle. The zonal span and longevity of these precipitation episodes exceed that of the typical convective system and are often attributable to a succession of MCSs.

In late July 1998, the central U.S. was host to a daily succession of such MCSs which propagated around the periphery of a subtropical ridge centered over Texas. For several days, precipitation was largely relegated to a narrow corridor in the vicinity of a strong instability gradient, with very little variation in its diurnal timing. In this paper we describe the environment near the convective systems by compositing numerical model analyses from the Rapid Update Cycle-2 (RUC-2). Fields are composited for different phases of the diurnal cycle. Additional composites are constructed with a coordinate system centered on the individual MCS and aligned with its direction of propagation. The interplay between the large-scale environment and the convection will be discussed from dynamical perspective.

extended abstract  Extended Abstract (432K)

Session 5, Mesoscale Processes and Convection
Tuesday, 13 August 2002, 4:30 PM-6:00 PM

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