Upward positive leaders (UPLs) in two artificially‐ initiated lightning flashes were imaged in three dimensions using VHF broadband digital interferometers and a high‐ speed video camera with time‐synchronized channel‐base current measurements. Locatable VHF sources of the two UPLs began at 1.1 km and 1.5 km, a few milliseconds after the UPL inception, and ascended to 2.4 km and 3.7 km, respectively, with average 3‐D speeds on the order of 106 ms⁻¹ . The initial stage currents for both flashes were unusually large and had peak values of 6 kA and 18 kA. VHF sources associated with positive leader propagation were located when the average current was higher than 3 kA and had significant pulse activity. The source altitudes and channel‐base currents suggest that there might have been a region of significant negative charge at altitudes from 2 to 4 km, which is below the freezing level of typical thunderstorms in Florida.