Sorces of Model Error, Page 2 of 9 No matter how fast computers become, their ability to forecast the weather will always be limited by the accuracy of the instruments used to observe the weather. Conversely, even with perfect instruments, the accuracy of a computer forecast is constrained by the ability to use the observations to construct an initial condition for the model with information at every grid point.
Instruments always have some inherent inaccuracy.
Because heights are computed from temperatures and pressures by integrating the hydrostatic equation, temperature errors cause errors in heights which get bigger at higher altitudes. Rawinsonde stations are typically more than a hundred miles apart, so each observation must represent conditions in the atmosphere over a large area. Suppose there are widespread thunderstorms, and the weather balloon ascends through the thunderstorm. On the other hand, if the balloon ascends in between clouds, the sounding will be relatively dry throughout the troposphere, and the thunderstorm will remain undetected. Either way, the observation will lead to an incorrect analysis even though the observation itself might be perfectly accurate.