Given the growing volume of forecast and observational data, it is becoming increasingly important for forecasters to extract relevant information quickly before and during severe weather forecast and warning operations. Thus, composite charts of model forecast fields and hourly surface analysis are presented to highlight the processes supporting severe storm development, convective organization, and storm mode. Composite charts are effective because they highlight important information, rather than exposing all possible information. By using color, images, and contours effectively, composite charts allow forecasters to quickly sort more from less important information, resulting in quick recognition of the convective potential.

The charts presented here focus on evaluating the large scale potential for severe weather with the Eta, and monitoring the real-time evolution of the convective environment with the hourly Rapid Update Cycle (RUC). In this context, RUC composite charts provide a link between synoptic scale model forecasts and an evolving real-time environment. Material composite charts include 1) measures of instability and vertical wind shear, 2) three dimensional moisture availability, content, and distribution and, 3) synoptic and mesoscale forcing mechanisms. By focusing on the processes that produce severe weather, forecasters can more confidently anticipate the probable range of convective evolutions for a given environment. During the event, composite mesoscale analysis charts constructed from the hourly RUC help forecasters understand ongoing convective evolutions, resulting in more effective warning operations.

Composite charts presented here were generated with AWIPS, and illustrate the large scale potential for a severe convective wind event that effected parts of Ohio, Pennsylvania, West Virginia, New York, and Maryland on 9 March 2002. Several model runs of the Eta indicated 1) significant vertical wind shear associated with strong tropospheric winds, 2) moderate moisture (dew points in the mid 50s) and, 3) considerable low-level forcing from a combination of strong moisture flux convergence and frontogenesis associated with a vigorous frontal system. The environment ahead of the front was forecast to become only weakly unstable, however, with CAPE forecast to remain less than 500 jkg-1, and the Best Lifted Index (BLI) expected to reduce no further than -2. The large scale potential thus suggested the possibility of a narrow frontal squall line with strong convective wind gusts, but weak instability would probably limit the areal extent of severe weather.

Composite mesoscale analysis charts presented here also reveal the evolution of the event in real-time, providing a critical link to the model forecasts, and strongly influencing the process of warning decisions. The hourly RUC composite charts illustrate the convective potential noted from Eta model forecasts, but also show that CAPEs were greater than 1300 jkg-1, and BLIs were -3 to -6 during the early evolution of the squall line. The environment had become significantly more unstable than the model forecast, indicating a high potential for widespread wind damage. This information was critical to understanding the evolving convective potential, resulting in exceptionally effective warning operations.