Comparison of forecast winds with those reported by aircraft on high altitude flights

After assessing the errors involved in deriving upper winds from a 200 mb contour and isotach chart, and considering also the likely error in "inflight" winds as computed by an aircraft navigator, it is concluded that computed and actual winds show reasonable agreement. Forecast winds are then compared with those computed and it is found that in 22 of the 25 zones considered, the forecasts are under-estimates, the root mean square difference ranging from 11.5 to 13.5 kt. Some of the reasons for this difference and the weakness of the forecasting technique adopted are then discussed.