Nowcast

Nowcast refers to the prediction of weather conditions on very short time scales, typically from minutes up to a few hours. It emphasizes rapidly changing phenomena such as precipitation, thunderstorms, and local wind shifts, and is distinct from longer-range forecasts which rely more on model guidance over days ahead. Nowcasting provides timely, highly localized information for decision making in aviation, emergency management, and outdoor activities.

Nowcasting methods combine real-time observational data and short-term dynamical understanding. Core data sources include radar reflectivity, satellite imagery (visible and infrared), weather station networks, rain gauges, and lightning detection. Two broad approaches are common: radar-based extrapolation, which tracks movement of observed precipitation features, and object-based or probabilistic methods that attempt to forecast the evolution of these features. Some systems blend extrapolation with brief numerical model guidance and physical constraints to improve skill.

Limitations include rapid structural changes in storms, radar sampling errors, clutter, and the potential for over- or underestimation as lead times lengthen within the nowcast window.

In addition to meteorology, the term nowcasting is also used in economics to describe real-time estimation of current economic activity, typically using high-frequency data sources to provide timely indicators of GDP growth or other aggregates before official statistics are released.