The Weather Bureau maintained by the United States Department of Agriculture displays at its stations flags which indicate probable changes in the weather.
A white flag indicates clear or fair weather.
A blue flag, rain or snow.
A flag with the upper half white and the lower half blue, local rain or snow.
A black triangular flag indicates temperature.
A white flag with black square in center, a cold wave.
When the black triangular flag is placed above the white flag, the black flag or the white and blue flag, it indicates warmer weather; when below, colder.
When the black triangular flag is not displayed at all, the temperature is likely to remain stationary.
Flags are displayed by the Weather Bureau as storm warnings in the following manner: