Example of GTG2 6–hour turbulence forecast as it appears on the Operational ADDS web site
Since it is a forecast product, the GTG is most useful for route planning, i.e., strategic avoidance of turbulence. However, given the rapidly evolving character of turbulence, for tactical avoidance it is more useful to have a rapidly updated nowcast system. This system, called GTGN (N for nowcast), is currently under development at RAL and is primarily driven by the most recent available turbulence observations (in situ EDR measurements, turbulence pilot reports, NTDA output, and satellite–based turbulence inferences) merged together with a GTG short–term forecast. The product updates every 15 min. It is scheduled for implementation on ADDS in the 2011–2013 time frame.
Example GTGN output (lower right) showing modifications from the GTG input (upper left).
The GTGN procedure uses GTG short–term forecast grids which are modified on a point–by–point basis to provide better agreement with the latest observations. The observations used include PIREPs, in situ EDR data, and NTDA EDR measurements. The gridded output is EDR. An example of the adaptive procedure is shown in the figure above.