by Ernest Thompson Seton
(Adopted for general use by the United States Signal Service on and after March 1, 1887.)
No. 1, white flag, clear or fair weather, no rain.
No. 2, blue flag, rain or snow.
No. 3, black triangular flag, refers to temperature, and above Numbers 1 or 2 indicates warmer weather; below Numbers 1 or 2 indicates colder weather, and when not displayed, stationary weather.
No. 4, white flag with black center (cold wave flag), sudden fall in temperature; this signal is usually ordered at least twenty-four hours in advance of the cold wave. It is not displayed unless a temperature of forty-five degrees or less is expected, nor is flag No. 3 ever displayed with it.
No. 5, means local rain or snow; with 3 above it means with higher temperature; and with 3 below it means lower temperature.
A red flag with a black center indicates that a storm of marked violence is expected.
