Today, few stations do manual analysis. Com-puters have for the most part replaced individual analysts. They are undoubtedly faster at deci-phering reports, evaluating data for continuity and accuracy, and producing a myriad of products worldwide. However, there are times when com-puter generated products arent available. At such times, you may be called upon to analyze upper level data. For this reason, and to better acquaint you with constant-pressure chart features, you should be familiar with analysis procedures. Just as there are recommended analysis procedures for the surface chart, there are similar procedures for constant-pressure charts. A recommended pro-cedure is as follows:

One basic consideration in the approach to all types of map analysis is that of history or con-tinuity. Upper-level features do not change radically in short periods of time. Consequently, a valuable aid in contour analysis of any given pressure level is the past history of the contours at that level. The study of previous maps is essen-tial, both as a key to the present situation and as a method of determining future movement and change in atmospheric systems.

Your first step in the analysis should be to check previous charts for accuracy, rationality, and any changes made to previous analyses based on information received after the analyses were completed. Fronts, troughs, and height centers do not normally appear and/or disappear in the 12 hours between analyses and any such occurrence should be viewed with suspicion. The past position of all height centers should be entered on the current chart for at least 24 hours. These positions are normally entered in black ink with an X circumscribed with a circle and connected with a dashed line. The time and date are entered above the circle. The corrected positions of all troughs and ridges should be transposed onto the current chart in yellow pencil. Knowing the past positions of features is your first clue in locating their present positions. When an upper-level feature moves into an area containing few or no reports, you may have to extrapolate its movement, construct the upper-level field from surface data, and/or deter-mine the new position from satellite pictures, if possible. Constructing the upper-level field from surface data is widely used in computer-generated products.

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