What Is Nowcasting?
Nowcasting is a form of very short-range weather forecasting, covering only a very specific geographic area. A nowcast is loosely defined as a forecast for the coming 12-hour period, based on very detailed observational data. A more restrictive definition of a nowcast is a detailed description of current weather conditions, from which one can extrapolate (project) the weather conditions for the following two hours.
Source: McGraw-Hill Encyclopedia of Science and Technology, 7th ed., vol. 12, p. 116.