A room temperature supersonic nozzle source beam was constructed as the target for a shock tube driven molecular beam. It is actuated electropneumatically and provides a few hundred microseconds of nearly constant intensity. The beam is formed from a supersonic flow by a two‐stage skimming process. In optimizing the configuration of skimmers and nozzle it was found that viscous regions in the system could be detected by observing the transient flux in the peripheral region around the beam.