The 0-6 hr forecasting (nowcasting) of thunderstorms has been historically based on the extrapolation of radar echoes or satellite cloud images. During the last few decades this has led to major improvements in severe storm warnings and advisories of high impact weather events. However, except for highly organized supercells or squall lines, the utility of extrapolation techniques decreases at a very rapid rate particularly during the first 60 min. Thus precision nowcasting of convective storms by extrapolation techniques is generally unreliable beyond 60 min because there is no accounting for storm initiation, growth and dissipation. Until recently there has been essentially no improvement in thunderstorm nowcasting beyond these simple extrapolation techniques.

In the last decade remarkable capabilities to anticipate storm initiation have been demonstrated by monitoring the location of boundary layer convergence lines, such as gust fronts, by radar and satellite. Physically based computerized nowcasting systems that assimilate knowledge of these convergence lines are now showing the ability to improve on extrapolation only techniques. It is believed that further improvement will require high resolution specification of the static stability and boundary layer winds; knowledge that is not routinely available. Recent exciting developments may be rectifying this situation. For example during the past four years high resolution boundary layer winds are being retrieved from single Doppler radar data. During the last year high resolution near surface water vapor measurements have been retrieved from radar data. A number of other very promising water vapor measurement techniques were also tested during the 2002 International H2O Project. In addition numerical modeling techniques which assimilate very high resolution data have shown promise. A sampling of new instrumentation and nowcasting techniques will be shown. Commentary on the future direction and accuracy of thunderstorm nowcasting will be presented. This will include the role of numerical models, automation, and the private and public forecaster.