Abstract A 12 h nested-grid numerical simulation of a warm-season mesoscale convective weather system (Zhang and Fritsch, 1986) is utilized as a control run in order to 1) test the sensitivity of the numerical simulation to different types of initial conditions; 2) examine the need for an observing system that would resolve mesoscale features; and 3) determine which meteorological variables need to be most carefully considered in observing system design and preprocessing analysis. It is found that improved observational capabilities are likely to have an important impact on the successful prediction of the timing and location of summertime mesoscale convective weather systems if mesoscale features can be resolved. In particular, the resolution of the moisture field significantly affects the prediction of the evolution of the convective weather systems. Correspondingly, the mesoscale distribution of precipitation is substantially affected, especially the location of the areas of heavy rain. It is also foun...