Abstract <p>Using the example of a catastrophic convective storm that occurred in Moscow region on June&#xa0;20, 2024, a study was conducted on the evolution of the potential vorticity and helicity based on information from a global hydrodynamic model and then a nonhydrostatic mesoscale model. A comparison of model data with weather radar information showed that a synoptic-scale tropospheric potential vorticity anomaly can serve as an indicator of the existence of convection. However, to specify the time and place of occurrence and development of active convection, a study based on information from a mesoscale nonhydrostatic model is necessary. If convection exists, mesoscale potential vorticity in the troposphere in the baroclinic zone are horizontally oriented dipoles of positive and negative anomalies. The integral helicity (0–3&#xa0;km) in the zone of active fronts also has a dipole structure, and a comparison of the integral helicity with an objective frontal analysis shows that negative helicity is present in the zone of cold fronts and positive helicity is present in the zone of warm fronts. In the zone of active convection, near the convective updraft flow, the structure of helicity calculated from the vertical component of vorticity is vortex dipoles—cyclonically and anticyclonically directed vortices, and in this zone, the same dipoles are formed in the structure of the mesoscale potential vorticity. Considering the occurrence of positive feedback between the mesoscale potential vorticity and helicity in the baroclinic zone, it is suggested to use the product of the gradient of the integral helicity in the layer from 0 to 3 km and the gradient of the mesoscale potential vorticity in the middle troposphere to determine the zones of occurrence of dangerous convective phenomena (thunderstorms, squalls, and heavy precipitation).</p>