Because of the individuality of jetstreams, and also because of the individuality of each situation with respect to humidity distribution and lower level circulation patterns, statistically stated relationships become somewhat vague and are of little value in forecasting. Compare short-range extrapolation techniques for the movement of frontal systems and associated weather. The purpose of this section is to outline several methods that are particularly suited to preparing forecasts for periods of 6 hours or less. The techniques presented are based on extrapolation. Extrapolation is the estimating of the future value of some variable based on past values.
Extrapolation is one of the most powerful short-range forecasting tools available to the forecaster.
Cloud observations received in synoptic codes permit only a highly generalized description of the actual structure of the cloud systems. Few forecasters make full use of the cloud reports plotted on their surface charts, and often, the first consideration in nephanalysis is to survey what cloud information is transmitted, and to make sure that everything pertinent is plotted. Either nephanalysis or surface charts should then be plotted at the intermediate times from 3-hourly synoptic reports or even from hourly sequences. An integrated system of forecasting ceiling, visibility, cloud cover, and precipitation should be considered simultaneously, as these elements are physically dependent upon the same synoptic processes. With present-day satellite capabilities, it is rare that a nephanalysis would be manually performed.