Coplanar barrier discharge in single-pair electrode configuration was used to study the formation of helium diffuse mode discharge. Transition from Townsend avalanching to the cathode and anode directed ionization waves was documented by high-speed camera imaging. When alumina dielectric barrier was coated by a thin layer of high permittivity coating (epsilon_r = 120–140), a new partial discharge preceding the Townsend avalanching phase was clearly visible. We suggest that this new pre-Townsend breakdown event is analogous to the known backward discharge of surface barrier discharge. Low magnitude of local electric field strength during the pre-Townsend breakdown reduces the number of competing electron collision excitation processes. This opens a new opportunity for studying optical emission from surface charge recombination processes.