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The daily weather map is a bird’s-eye view of the United States with respect to temperature, pressure, wind, and storm at 8 o’clock in the morning, seventy-fifth meridian, standard time. A few minutes before 8 o’clock more than two hundred observers are busy recording all weather conditions covering the various stations. These observations are completed by 8 o’clock, morning and evening, and are promptly telegraphed to the Weather Bureau at Washington in coded form. So carefully and thoroughly is the work done that a few code words from each station contain all the necessary information concerning temperature, pressure, direction of the wind, rain or snow, cloudiness, moisture, thunder-storms, fog, and other phenomena.

Making the Daily Weather Map.—At the central office, and also at certain other designated offices, the figures and other information are charted on a base map containing the name and position of each station, the boundaries of the states, and the outline of the United States. For the sake of clearness, all other features and names are omitted. Blue lines are drawn to indicate isotherms; red lines similarly indicate isobars. When the isobars are completed it will be found that some of them are roughly concentric, inclosing irregularly shaped ellipses. In some of these the pressure is highest at the center; in others, the center is the point of lowest pressure. These are the highs and the lows that indicate storm centers—that is, anticyclones and cyclones.

In order to give the forecaster additional information, the direction of the wind and the sky condition must be noted. These are shown in each case by a circle pierced with an arrow.