Nowcasting

Nowcasting comprises the detailed description of the current weather along with forecasts obtained by extrapolation for a period of 0 to 6 hours ahead. In this time range it is possible to forecast small features such as individual storms with reasonable accuracy. A forecaster using the latest radar, satellite and observational data is able to make analysis of the small-scale features present in a small area such as a city and make an accurate forecast for the following few hours. It is, therefore, a powerful tool in warning the public of hazardous, high-impact weather including tropical cyclones, thunderstorms and tornados which cause flash floods, lightning strikes and destructive winds. In broad terms, nowcasting contributes to the:

•          reduction of fatalities and injuries due to weather hazards;
•          reduction of private, public, and industrial, property damage; and to
•          improved efficiency and savings for industry, transportation and agriculture. 

In addition to using Nowcasting for warning the public of hazardous weather,  it is also used for aviation weather forecasts in both the terminal and en-route environment, marine safety, water and power management, off-shore oil drilling, construction industry and leisure industry. The strength of nowcasting lies in the fact that it provides location-specific forecasts of storm initiation, growth, movement and dissipation, which allows for specific preparation for a certain weather event by people in a specific location.

Extrapolating radar echoes is the mainstay of Nowcasting. This is because radar data is very detailed and picks out the size, shape, intensity, speed and direction of movement of individual storms on a practically continuous basis.  This makes it possible to extrapolate the likely location of a moving storm. The intensity of rainfall from a particular cloud or group of clouds can be estimated, which gives a very good indication as to whether to expect flooding, the swelling of a river etc. Depending on the area of built-up space, drainage and land-use in general, a forecast warning tailored to the safety and well-being of a particular community may be issued. In order to extend the time period of Nowcasting beyond 6 hours, some Nowcasting systems use the combination of radar extrapolation techniques with satellite and Numerical Weather Prediction (NWP) model products to produce an extended short-period forecast.

Given the utility of Nowcasting, it is desirable that every National Meteorological and Hydrological Service (NMHS) develops its PWS capacity to effectively render Nowcasting Services to the public.

 Proceedings of a meeting of the experts on the application of Nowcasting techniques to PWS are available on this website.