Nowcasting of precipitation systems

Abstract

Digital remotely sensed observations of the atmosphere, particularly from radars and satellites, have become increasingly available over the last 15 years. Together with developments in computer technology this has stimulated the design and operation of a variety of systems to exploit these data in weather forecasting. Growing awareness of the importance of detailed site specific weather information and forecasts from zero to a few hours ahead has led to the emergence of a particular kind of forecasting called nowcasting which depends on the exceptionally detailed knowledge of the current pattern of weather that remote sensing can provide. This type of weather forecasting is reviewed, with emphasis on the measurement and extrapolation up to about 2 hours ahead of fields of various weather parameters, especially rainfall. Trends in the design of nowcasting systems are discussed, and potential benefits summarized. tion of the weather, have been available to forecasters in real time and in a digital form amenable to manipulation. Although the preparation of forecasts by extrapolating the observed fields might be regarded as a simple extension of what forecasters have done for generations, limitations in observing capability and understanding of mesoscale phenomena, together with the practical difficulties of handling vast quantifies of data quickly, make this a challenging task in practice.Since extrapolation is the basis of nowcasting systems, the quality of the resulting forecasts depends upon the time ahead for which linear extrapolation is valid. This varies for different weather systems as shown in Table 1. Frontal rainbands, for example, persist for many hours. However, severe weather caused by individual convective systems is short-lived, and linear extrapolation on its own is unlikely to provide good forecasts beyond an hour or so. The larger-scale systems with greater persistence, such as fronts, often act as the trigger for the smaller convective Published in 1989 by the American Geophysical Union. ß 345 ß Reviews of Geophysics, 27, 3 / August 1989 pages 345-370 Paper number 89RG01134 346 ß Browning and Collier: NOWCASTING OF PRECIPITATION SYSTEMS 27, 3 / REVIEWS OF GEOPHYSICS storm/blizzard High wind gusts 5-30 min very limited accompanying shallow showers Hurricane many hours fair Frontal passage many hours fair to good After Zipser [ 1983]. (Part of this table is from Doswell [ 1986].) 27, 3 /REVIEWS OF GEOPHYSICS Browning and Collier: NOWCASTING OF PRECIPITATION SYSTEMS ß 347 when and where it will be triggered, unless there is some well-def'med topographical forcing, for example. We shall not discuss the nonlinear methods further in this review; rather we concentrate on the conceptually simple linear nowcasting techniques that have been developed to characterize, track, and extrapolate the motion of existing weather features detected by mdars and satellite. At present, nowcasting systems in several countries are providing data for severe weather warning, hydrological forecasting, snow clearance on roa...

INCA-CE: a Central European initiative in nowcasting severe weather and its applications

“…Most existing observation-based forecasting systems focus on the prediction of precipitation and convective activity (Browning and Collier, 1989;Li et al, 1995;Hand, 1996;Golding, 1998;Pierce et al, 2000;Seed, 2003). During the World Weather Research Program (WWRP) Forecast Demonstration Project of the 2000 Sydney Olympics several of these methods were tested and compared .…”

Very short period quantitative precipitation forecasting

“…Most notable was the Met Office in the United Kingdom, which introduced first the FRONTIERS (Browning and Collier, 1989), and then the Nimrod systems (Golding, 1998). The major innovation of the latter of these systems was the combination of radar extrapolation techniques with NWP model precipitation products to produce an extended short-period forecast that was consistent with larger-scale and longer-period forecasts (Golding, 2000).…”

Peak Flow Forecasting with Radar Precipitation and the Distributed Model CASC2D

“…A term that is often used to describe real time generation of precipitation forecasts from radar data is "nowcasting." Browning and Collier (1989) present a review of several nowcasting techniques in which they state that weather prediction models can provide precipitation forecast data, and although these models are improving in spatial resolution, they operationally may not be able to provide the level of detail that is desired for hydrologic forecasting in real time. They further state that for short-term forecasts of a few hours, a reasonable forecast can be achieved by assuming that the current rainfall pattern and movement will continue without change over the short time period of interest into the future.…”