Nowadays, we have radio, TV and the internet to tell us when a cold front or other weather is headed our way. In the late 19th and early 20th centuries, signal flags were used to alert U.S. citizens to weather conditions.
Postcard of the U.S. Weather Bureau Building at Charles City, Iowa. c. 1900. Note the Weather Forecast Flag system flags flown on the flag pole mounted on the roof. They appear to be the blue flag with a black pennant above, indicating a forecast of higher temperatures and rain. (Image credit: Courtesy of Steve Doty, NOAA NCDC (ret.))
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The origin of weather signal flags
Weather signal flags grew out of the use of the maritime signal flag, which was red, with a black square inside. Starting in 1871, this flag was used at 20 ports on the Atlantic and Gulf Coasts, as well as the Great Lakes.
In 1878, the Army Signal Service’s Weather Bureau began flying coded flags outside weather buildings and post offices to share forecasts with locals.
The original weather signal flags included a red circle, crescent, and star for warmer, cooler, and steady temperatures, respectively. A blue circle, crescent, and star indicated general rain or snow, fair weather, and local rain or snow. A special white flag with a black square in the center indicated a sudden cold wave moving through.
A new look for weather signal flags
By the early 1890s, the flags had been updated. The circles, crescents, and stars were replaced by a new system. This included a white flag for fair weather, blue for precipitation, and horizontal bars of white above blue for local rain. A black triangular flag was placed above one of these flags for warmer weather and below for colder weather. When the temperature remained about the same as the day before, the black triangular flag was not displayed. The cold wave flag remained unchanged. It was never flown with the black triangular flag, as it already indicated a sharp temperature drop.
The network grows
By 1886, 290 locations were capable of displaying these weather flags and the forecast could be relayed further by telegraph, telephone, and railway. They were so popular that W.B. Hazen, the Chief Signal Officer at the time, recommended that $5000 be allocated in the 1886-87 fiscal year to expand the network.
"There is no feature of the service which has proven more valuable, and the system should be extended to every town in the United States, and also to stock agricultural districts when practicable," W.B. Hazen wrote in the Annual Report of the Chief Signal Officer of the Army to the Secretary of War.
Wind and hurricane weather signal flags were added in the mid-1890s and a series of vertical lights was added in 1916 for nighttime use.
New technologies improve weather warnings
In 1927, the Weather Bureau decided to begin phasing out their use of weather signal flags. They would purchase no replacements once their existing stock of flags had been exhausted. However, the flags remained in use in some areas until the 1960s.
As radio and television became more popular, these flags were no longer needed, but today’s National Weather Service still issues weather warnings to inform and protect the American public and is always working to improve that capability.
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