Although no actual experience of aircraft operations at 30000 and 40000 ft was available on the Sydney - Nandi route, an attempt was wade to assess the likely order of accuracy pf forecasts of wind and temperature at these heights on the route. As background data, the standard deviation of wind and temperature and statistics relating to the variation of wind in time and space were derived for stations near the route. As these statistics are not available elsewhere they have been included in the article. Using upper air analyses which contain an unknown error, a subjective assessment was made of the errors in 24-hr forecasts of wind and temperature. By the use of statistical relations errors in 24-hr point forecasts were used as a check on the errors in 24-hr equivalent head winds over the route. Statistical relations were also used to assess, from 24-hr EHW forecasts, likely errors in shorter period forecasts. An assessment was also made of the probable error in forecasting by statistical methods. All methods indicated a RMS error in wind forecasts of about 15 kt for forecasts made 8 to 20 hr after the time of observations. Using the assessed errors in 24-hr forecasts of temperature over four zones of the route and 24-hr temperature forecasts for points near the route, RMS errors in temperature forecasts for periods of 8 to 32 hr were assessed to range from 2.5°C in the western zone to 2°C in the eastern zone.
McRae et al. (Mon,) studied this question.