A gas assisted liquid spray nozzle assembly having a nozzle body that defines a mixing zone, a liquid inlet communicating with the mixing zone from a side thereof, and a pressurized gas inlet communicating with the mixing chamber from an upstream end. The liquid inlet includes a liquid inlet extension and diffuser post extending transversely into the mixing zone having a liquid extension passageway and a closed downstream end that defines an internal impingement surface disposed on a central axis of the mixing zone against which liquid impinges and is transversely directed into the mixing zone for atomization by pressurized gas directed centrally through the mixing zone from the gas inlet. The spray nozzle assembly includes a barrel extension zone downstream of said mixing zone with a spray tip for directing the atomized liquid in a predetermined spray pattern.