Problems in Weather Map Analysis and Forecasting in Connection with Transatlantic Flying

Abstract

T following remarks are based in part on the author's experience of the past summer in forecasting for the transatlantic survey flights of the American Export Airlines, and in part on experience gained during the past three years in the analysis of Northern Hemisphere weather maps, together with the analysis of North American aerological data. Any discussion of transatlantic flight forecasting must be prefaced by a few general remarks on the basic requirements of such a service. It must be borne in mind that efficient transatlantic flight operations, especially in winter, will require dependable weather forecasts over a stretch of some 3000 miles of open ocean, extending from 48 to 72 hours ahead. This presupposes quite a different type of forecasting than, for instance, that required by domestic airlines, where usually an accurate 12-hour forecast, or at most one for 24 hours, is sufficient to meet individual flight needs. Furthermore, all the local topographical features of the flight region which are so important to much of the domestic airlines forecasting largely disappear in transoceanic forecasting. In other words, the transoceanic service calls for more emphasis on the basic long-range general type of forecast, with particular emphasis on winds aloft, rather than the typical short range specialized aviation forecast. The greater the time and space range of a forecast, the more important becomes the general basic forecast, and the less important the localized special details which are emphasized in the aviation type of forecast. Apart from the winds aloft, the occurrence of zones of heavy icing is the only characteristically aviation forecast item which needs to be stressed in the transatlantic flight forecasts. Not only in comparison with domestic aviation forecasting, but also in comparison with flight forecasting for the present transpacific routes and the routes to Central and South America, the Atlantic forecast service offers peculiar difficulties. The Atlantic flight routes lie far enough north so that they come within the zone of strong cyclonic activity in winter, with its rapidly changing conditions and frequent strong winds over large areas. The Pacific and South American routes occasionally are affected by strong extra-tropical cyclonic activity, and occasionally by tropical disturbances, but by and large, conditions on those routes are comparatively steady and winds moderate. The