High-resolution total column ozone data from the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS) are used in conjunction with potential vorticity (PV) from NCEP's Rapid Update Cycle (RUC) and Eta mesoscale model analyses to examine the role of stratospheric air and rapid PV fluctuations in two severe weather events accompanied by pronounced stratospheric intrusions. Backward trajectories, determined from the Eta model, were used to examine the role of descending dry stratospheric air in severe weather not associated with thunderstorms and within severe thunderstorms. Agreement between the total ozone and PV data supported the notion of stratospheric descent. Detailed vertical structure in the PV appears to be captured by small-scale variations in the total ozone. Also, the total ozone data identified mesoscale features that may be useful in model verification. In addition, the total ozone data was able to distinguish between PV of stratospheric origin and PV diabatically generated in the troposphere. Another severe weather event analyzed exemplifies the need to use chemical traces, such as ozone and water vapor, in addition to isentropic PV to indicate air mass origin. This particular case appeared to have enhanced total ozone concentrations unaccompanied by high PV values. Again, backward trajectories from the Eta model were used to discern the diabatic or diffusive processes that may have been responsible for the lack of correlation. These results are significant to tropospheric-stratospheric exchange studies indicating that isentropic PV alone is an insufficient indicator of air mass origin.