Postmaster Frank Haskell ran a local weather bureau at the post office beginning in August of 1891. Each day he received a telegram from St. Paul telling the forecast for the next 24 hours. He had a flag pole installed in front of his post office and would raise Signal Service Flags of different colors and designs to indicate weather conditions.
The following is a description of the different flags:
No. 1, white flag, clear or fair weather
No. 2, blue flag, rain or snow
No. 3, white and blue flag, local rains
No. 4, black triangular flag, temperature signal
No. 5, white flag with black square in center, cold wave.
INTERPRETATION OF DISPLAYS
No. 1, alone indicates fair weather, stationary temperature.
No. 2, alone, indicates rain or snow stationary temperature.
No. 3, alone, indicates local rain, stationary temperature.
No. 1, with No. 4 above it, indicates fair weather, warmer.
No. 1, with No. 4 below it, indicates fair weather, colder.
No. 2, with No. 4 above it, indicates warmer weather, rain or snow.
No. 2, with No. 4 below it, indicates colder weather, rain or snow.
No. 3, with No. 4 above it, indicates warmer weather with local rains.
No. 3, with No. 4 below it, indicates colder weather with local rains.
No. 1, with No. 5 above it, indicates fair weather, cold wave.
No. 2, with No. 5 above it, indicates wet weather, cold wave.
Source: Cooperstown, North Dakota 1882-1982 Centennial Page 265