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

Wednesday, 1 August 2001
Analysis of warm-season morning convection across the southern Great Plains
John A. Haynes, CIMMS/Univ. of Oklahoma, Norman, OK; and C. E. Hane, D. L. Andra, E. Berry, F. H. Carr, and R. M. Rabin
Poster PDF (49.6 kB)
Warm-season mesoscale convective systems (MCSs) impact much of the United States with heavy rains, and often severe weather, primarily during nighttime hours. These systems typically dissipate or decline in intensity during the four hours or so before local noon. However, some are maintained or regenerate and continue into the afternoon. The Morning Convection Project (MCP) was begun for the purposes of better understanding the factors that influence late-morning (0900-1700 UTC) MCS evolution, and to provide tools that can be used to improve short-term forecasting of these systems. The MCP is a collaborative effort among the National Severe Storms Laboratory, the University of Oklahoma, and the National Weather Service Forecast Offices in Norman, Oklahoma, and Dodge City, Kansas.

An effort has been made to assess the factors that are currently felt to be most important in short-term forecasts of evolution for these morning systems. National Weather Service forecasters at the two offices provided real-time input on a subset of those convective systems that occurred within the period of interest during the summers of 1997-2000. A summary is given, based on their comments, listing the factors that were felt to be most important in their forecast of system evolution during the late morning period. The environmental factors that were listed most often included system-relative winds and shear ahead of systems, environmental stability, and the presence of upper level short-wave troughs.

Results of a climatological study of morning systems are described in which characteristics of almost 150 individual MCSs that occurred during the summers of 1996-2000 within the County Warning Areas (CWAs) of Norman and Dodge City were investigated. In addition to occurrence within the CWAs in the 0900-1700 UTC period, included systems had to meet criteria relating to system motion, size, duration, and intensity. Systems were chosen based upon examination of hourly mosaic images from the National Climatic Data Center (NCDC) archive of NEXRAD national reflectivity and upon the NCDC archive of individual station WSR-88D Level II data. Surface and upper air charts were also examined, as well as maps indicating cloud-to-ground lightning within specified time periods. The climatology included for each system the track, initiation mechanism, character of evolution, occurrences of severe weather, and occurrences of cloud-to-ground lightning.

A summary is given of preliminary results that include the relation of system evolution to the environmental wind profile ahead of each system. Data for calculation of wind characteristics was obtained from an archive of the Rapid Update Cycle (RUC) analyses. Plans for future work as part of this project-in-progress are also summarized. These include system evolution in relation to static stability changes, evaluation of theories relating wind characteristics to system evolution, and assessment of an operational model in its ability to predict environmental fields that are significant factors in the evolution of these systems.

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