NOAA-NESDIS
Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Friday May 9, 1997
    The two visible images below from 1715 Z and 2015 Z Mar 14, 1997 demonstrate boundary interaction in the initiation and movement of thunderstorms. On this day a cold front was moving through Texas, the 18 Z NMC surface analysis showed the cold front just on the Texas coast. The front can be identified on the 1715 Z image as the narrow cloud band which parallels the coast (marked by light blue arrow). Moving out ahead of the front was an impressive morning glory. If you follow the leading cloud band of the morning glory (marked by red arrow) back inland, you'll notice that it ends in a large cumulus cloud (marked by black arrow). Extrapolate the cold front described above and you'll see that the enhanced cumulus appears to form at the intersection of the front and the morning glory.

    At 2015 Z a thunderstorm which developed out of the enhanced cumulus can be seen on the Texas/Mexico border, south-southeast of the enhanced cumulus seen at 1715 Z. NMC placed the cold front just off the coast at 21 Z, corresponding with the thin cloud band off of the Texas coast (again marked by light blue arrow). The interpretation is that the thunderstorm exists at the intersection of the cold front and the leading cloud band of the morning glory (again marked by red arrow).

    Consider again the motion of the storm, to the south-southeast. At 00Z Mar 15, 850 mb and 700 mb winds at BRO were southwesterly, the middle and upper level winds (note direction of thunderstorm anvil for upper level winds) were westerly. In this case the thunderstorm apparently followed the movement of the intersection of the two boundaries, and not the mean winds. I say apparently, however, because at 12 Z 14 Mar, BRO had north-northwesterly winds at 700 mb, northwesterly winds at 500 mb and 300 mb, and west-northwesterly winds at 200 mb. So depending on what the vertical wind profile in southern Texas was between 1715 Z and 2015 Z, the environmental winds may have assissted in the direction of the storm's movement. But seeing how the upper level winds as shown in the anvil were more closely related to the 00 Z 15 Mar vertical wind profile, the boundary movement most likely had some, if not most of the influence on storm motion. Storm motion dictated by boudaries as opposed to evironmental flow does occur and should be considered.

    Jack Dostalek

    We welcome your comments and discussion at ramsdis@comet.ucar.edu