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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D08108, doi:10.1029/2007JD009063, 2008

Investigation of stability characteristics of cold-season convective precipitation events by utilizing the growth rate parameter

Christopher J. Melick

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Patrick S. Market

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Larry L. Smith

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Brian P. Pettegrew

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Amy E. Becker

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Anthony R. Lupo

Department of Soil, Environmental and Atmospheric Sciences, University of Missouri-Columbia, Columbia, Missouri, USA


Abstract

The seldom utilized growth rate parameter (σ 2), which predicts how rapidly a small-amplitude disturbance will grow in a conditional symmetrically unstable environment, was applied to study the stability characteristics of convective precipitation case studies across the central United States during the winter seasons of 2003–2004 and 2004–2005. The goals were to improve our understanding of how the environment becomes destabilized over a relatively short period of time, as well as to determine approximately where and when elevated thunderstorms are likely to develop. The comprehensive evaluation comprised a case study example and summary of statistics obtained by tabulations at the initiation site and spatial compositing of all case studies identified. The doubling time for the convection (the time required for a convective element to achieve twice its current depth) was found to be on the order of 1.3 h, which is consistent with the typical timescale for moist slantwise convection resulting from the release of conditional symmetric instability. The development of cold-season precipitation with lightning (i.e., thundersnow) and any associated banding was correctly and most accurately predicted from trends in plots of σ 2 analyzed at the level at which the highest significant growth rates occurred. While this naturally varied from one event to the next, the average elevation tended to be close to 650 hPa. Furthermore, a term-by-term diagnosis of the mathematical expression for the growth rate was determined to be quite useful as another means of identifying the type of instability released within instances of wintertime convection. By calculating the individual contributions to the growth rate and observing whether a positive or negative response was obtained, the nature of the stability regime present was also ascertained. The inclusion of a set of non-thundering snowstorms helped to substantiate the assumption that atmospheres are less stable and more susceptible to vertical motions during those occasions where lightning develops in wintertime scenarios. Thus an outlook for elevated, cold-season thunderstorms can be more accurately issued by identifying regions where reduced values of equivalent potential vorticity (i.e., small symmetric stability or instability) are collocated with estimates of high σ 2 (i.e., where small-scale slantwise perturbations will grow). Given the overall success, it is hoped that some of the conclusions established by this work will be implemented routinely in an operational environment and provide forecasters an additional, essential tool in dealing with nowcasting situations of hazardous winter weather events.

Received 12 June 2007; accepted 19 December 2007; published 22 April 2008.

Keywords: Growth rate; banded convection; thundersnow.

Index Terms: 3364 Atmospheric Processes: Synoptic-scale meteorology; 3329 Atmospheric Processes: Mesoscale meteorology; 3314 Atmospheric Processes: Convective processes; 3354 Atmospheric Processes: Precipitation (1854); 3324 Atmospheric Processes: Lightning.

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Citation: Melick, C. J., P. S. Market, L. L. Smith, B. P. Pettegrew, A. E. Becker, and A. R. Lupo (2008), Investigation of stability characteristics of cold-season convective precipitation events by utilizing the growth rate parameter, J. Geophys. Res., 113, D08108, doi:10.1029/2007JD009063.