This section deals with the Lemon Technique of severe storm detection by radar, designed for environments with moderate to strong vertical wind shear. We have seen that strong shear causes weak updrafts to slope from the vertical, whereas stronger updrafts are able to withstand the shear and assume a more vertical character. The Lemon Technique, and modified versions such as the WRIST technique, allow the radar operator to infer the strength of the updraft through three-dimensional visualization of the radar-detectable rainy downdraft surrounding the updraft. We stress that the radar operator must perform the vertical tilt sequence employed in these techniques to determine storm structure and classification properly.

[Image: lemon technique to analyze thunderstorm (61K)]

This diagram represents a weak, non-severe storm (most likely multicellular) in a sheared environment. The top figure is a westward view of a vertical cross section of the storm, whereas the bottom diagram is a horizontal, low-level cross section. (Note line A-B in the lower figure, which corresponds to the vertical cross section.) Precipitation and rainy downdraft descend downwind (usually northeast) from near the summit of the tilted cloud. The radar PPI echo, the bottom figure, has a concentric reflectivity configuration, with the highest top over the center of the low-level echo maximum. Note the orange arrow, which represents the trajectory that air parcels take into the storm, through the updraft, and out of the storm through the downwind anvil.

This thunderstorm was developing in a strongly-sheared environment in the northeast Texas Panhandle. The severe slope of both the updraft and its trailing flanking line towers is quite obvious in this view, looking north from about 30 miles.

One of the tops, about half way along the flank and slightly behind the first row of flanking towers, had assumed a slightly more vertical appearance. The storm was a small VIP 4 on radar at this time with its top situated over the low-level echo.

introduction

Terms for using data resources. CD-ROM available. Credits and Acknowledgments for WW2010. Department of Atmospheric Sciences (DAS) at the University of Illinois at Urbana-Champaign.

multicell lt-analysis