Figure 22.  Observed surface temperature (deg F) analysis at 1600 UTC April 6 2003. The yellow vectors directly relate to the orientation and magnitude of the surface thermal gradient (deg C/m). The red '-' and '+' represent locations of lightning strikes during the previous hour (NLDN). While the primary thermal gradient is associated with the synoptic front farther north, this analysis clearly shows the thermal gradient associated the boundary across northeast Louisiana and central Mississippi ahead of the convective precipitation associated with the first MCS. is the U.S. government's official web portal to all federal, state and local government web resources and services.