18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Wednesday, 1 August 2001
Vertical structure and characteristics of two leading stratiform mesoscale convective systems
Crystalyne R. Pettet, Colorado State University, Fort Collins, CO; and R. H. Johnson
Poster PDF (3.8 MB)
Parker and Johnson (2000) documented three classes of linear mesoscale convective system (MCS) organization: a convective line with trailing stratiform (TS), leading stratiform (LS), and parallel stratiform (PS) precipitation. While a great deal of research has been done to document the structure of TS MCSs, there is very little in the literature on the other two modes. This study investigates two LS cases: a 30 April 2000 storm in Oklahoma, and a 7 May 1997 system in South Dakota and Iowa. The datasets available for these two cases differed. Wind profiler and Oklahoma mesonet data are used in analyzing the 30 April case, while Doppler radar data are used for the 7 May case. RUC reanalyses and soundings are used for both cases.

Vertical cross sections of gridded wind profiler data, as well as the RUC reanalyses, show evidence of a low-level rear inflow to the 30 April MCS. This "feeds" the LS high theta-e air and with the stratiform precipitation advancing ahead of the convective line, this air has not been cooled by travelling through the stratiform precipitation region. Lack of a strong cold pool keeps the system relatively stationary, allowing for the redevelopment of cells over the same area and contributing to flash flooding that occured with this storm. A leading mesolow is evident in the mesonet data which moves to the southeast, along the stratiform area. Further analysis of this mesolow indicates it has gravity wave-like features. A descending leading inflow jet appears in the data, a mirror image of the rear inflow jet commonly observed in TS systems. This feature could be responsible for heat bursts that occur ahead of and beneath the stratiform area. In a broad sense, features in the 30 April LS MCS appear as a mirror image of typical TS structure. However, the convective line in this LS system is far more discontinuous.

Doppler radar analyses of storm relative radial velocity for the 7 May case indicate the presence of an elevated rear inflow at 3 km. This high resolution dataset supports the findings of the coarser profiler data in the 30 April case. There is evidence of descending leading inflow, but it is not as prominent as the 30 April case. The storm relative radial velocity cross sections also depict rising rear-to-front flow at upper levels which causes ice crystals to blow downstream and form the stratiform precipitation ahead of the convective line. Vertical cross sections of radar reflectivity show a significant bright band progressing ahead of the convective line with a transition zone of low reflectivity dividing the two areas. This also appears as a mirror image of typical TS structure. RUC reanalyses, although they have lower resolution than the mesonet data, show a stronger cold pool for the 7 May case than the 30 April case.

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