Useful tool for determining the location of initial convection when forcing mechanisms are weak. Heavy rainfall producing convection often develops within or along the upstream edge of a vorticity minimum ridge axis at 500 mb. Watch for convection behind a weak shortwave if moist unstable inflow persists into a low-level boundary. The convection then is maintained by low-level forcing. If a well-defined middle and high level tropical moisture connection exists in water vapor imagery, rain potential is typically higher than normal.
Inverted isobars signal the possibility of heavy rainfall.
Elevated thunderstorms with attendant heavy rainfall often fit the synoptic patterns described by Maddox et al. Small MCSs were associated with a weaker front, if present, which was not subject to frontogenetical forcing. Frontogenetical forcing typically enhances the direct thermal circulation pattern and thus the subsequent convective activity. Glass et al.