Hoist a Flag for Cold waves and Other Weather Conditions

Posted
Last Updated

By noaa.gov.

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.

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.

Illustration of the Signal Service flags used in 1886.

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

Excerpt from the 1894 edition of Bureau of Navigation’s "Merchant Vessels of the United States."

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.

A 6 foot by 6 foot cold wave flag provided to the U.S. Weather Bureau as a sample of an unknown company’s work sometime in the late 19th or early 20th century.

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.

read more at noaa.gov.

Image Credits: 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.))
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.))