Weather Signal
a signal for indicating weather conditions. Five flags are used by the United States Weather Bureau to indicate the temperature and ordinary conditions of the weather. They are numbered 1 to 5, but some are used in couples to form combinations. No. 1 is a perfect white square and indicates "clear or fair weather." No. 2 is all blue, also square, and its meaning is "rain or snow." No. 3 is a black triangle and is called the "temperature signal." It is always used in combination with either the white or blue square.
When placed above the white or blue flag it means that the weather will be warmer, and when below, that it will be colder. When it is omitted altogether, the significance is that the temperature wings, long tails, and very bright coats, will be stationary. Sometimes three be stationary.
Sometimes three flags are used in combination. For example, when the triangular flag is at WEAVER BIRDS AND NEST the latter often varied in the breeding season. the top of the pole, with the white square WEAVING, the art of interlacing وو immediately below it, and the blue square below the white, the signal reads "warmer, fair weather, followed by rain or snow." No. 4 is the "cold wave" signal. It is a white square with a black square in the center of the white. It shows up very clearly, and can never be mistaken for anything else. No. 5 indicates "local rains or showers." It is a square flag, of which the upper half is white and the lower blue. See WEATHER BUREAU.