Convective-scale data assimilation and nowcasting
Nowcasting is the prediction of weather with 0 to 7 hour lead times. This is vital for the prediction of severe weather, in particular flooding events.
Nowcasts of rainfall and associated weather, such as hail and lightning, are the most widespread and advanced applications, though temperature, wind and other weather elements are also produced in some systems.
Traditionally nowcasting has been done by human weather forecasters or by computer-based extrapolation techniques of the current or most recent observations, particularly radar and satellite observations. Increases in available computer power allowing faster, more complex models with higher resolution mean that it is now possible to start developing an NWP-based nowcasting system - this will allow for prediction of initiation, development and decay of storms, by use of fundamental fluid dynamics and physical processes, which pure extrapolation techniques cannot represent.
A major challenge is to exploit available observations, especially high resolution ground and satellite based remote sensing, to describe the initial conditions for the nowcasts using data assimilation.
At MetOffice@Reading a 1.5km resolution NWP-based hourly nowcasting system producing forecasts from 0 to 7 hours was developed to use surface observations, radar radial Doppler winds, radar derived surface rain rates, Meteosat satellite imagery, wind profiler, GPS and aircraft data using 3DVAR and 4DVAR data assimilation methods. Nowcast forecasts have to be available very quickly after the time of the observations which is challenging not only for the data assimilation and NWP systems but also for transmission and pre-processing of the observations. A system known as the Nowcasting Demonstration Project for the London 2012 Olympic and Paralympic Games was run in real-time from March 2012-April 2013 and work has now transferred to the Convective-Scale Data Assimilation Team, based in Exeter, to produce an operational system for the whole UK
- Development of efficient NWP-based nowcasting system for forecasting high impact weather
- Exploitation of novel data sources such as radar, geostationary imagery, high resolution polar orbiter sounding data and ground based remote sensing
- Improved forecast systems for flooding from intense rainfall.
- Development of techniques to directly assimilate radar data such as radial Doppler winds, reflectivity and refractivity and ceilometer backscatter profiles and geostationary satellite imagery at 1.5km resolution.
- Development of techniques for improved specification of forecast background errors and correlated observations errors at 1.5km resolution.
- Collaboration with UK universities.