Before World War II, weather forecasters had little knowledge of upper-air wind patterns above 20 000 feet. Data were seldom available at these heights, and the need was not great because commercial aircraft seldom flew at these altitudes. The war in the Pacific changed all that. Wind forecasts for 30 000 feet plus became urgent to support the XXI Bomber Command in its bombing mission over Japan.
The U.S. Army Air Force Pacific Ocean Area (AAFPOA) placed a Weather Central in the Marianas Islands in 1944 (Saipan in 1944 and Guam in 1945) to provide forecasting support for this mission. A forecasting procedure was put into operation that combined the elements known as “single-station forecasting” and an advanced procedure that used “altimeter corrections” to analyze upper-air data and make prognoses. Upper-air charts were drawn for constant pressure surfaces rather than constant height surfaces. The constant pressure surfaces were tied together by means of the atmospheric temperature field represented by specific temperature anomalies between pressure surfaces. Wind forecasts over the Marianas-Japan route made use of space cross sections that provided the data to forecast winds at each 5000-ft level to 35 000 ft along the mission flight path. The new procedures allowed the forecaster to construct internally consistent meteorological charts in three dimensions in regions of sparse data.
Army air force pilots and their crews from the Marianas were among the first to experience the extreme wind conditions now known as the “jet stream.” Air force forecasters demonstrated that, with experience, such winds could reasonably be forecast under difficult operational conditions.