Winter is coming. For the next three months or so, we face cold temperatures, blustery winds, chilly rains, occasional snow and ice storms, and regular frosts. Living in the 21st century, accurate foreknowledge of unpleasant or dangerous weather is available at our fingertips. It was decidedly different in the 18th century.
Just like we are today, people in the past were captivated by the weather and urgently wanted to know what it was going to do. George Washington was fascinated by the weather. His preoccupation stemmed, of course, from his occupations as a surveyor, soldier, and planter. Washington’s lifetime of diaries are filled with meteorological observations like this one from December 13, 1799. “Morning Snowing & abt. 3 Inches deep. Wind at No. Et. & Mer. at 30. Contg. Snowing till 1 Oclock and abt. 4 it became perfectly clear. Wind in the same place but not hard. Mer. 28 at Night.” This particular weather observation by Washington would also prove to be his final diary entry. He died about 24 hours later. Given his passion for the weather, it actually seems quite fitting that among the man’s last documented words there would be a weather report.
Accurately predicting the weather certainly would have helped Washington in his surveying, soldiering, and planting and weather forecasting was not completely impossible in the 18th century. People in Washington’s time had some primitive tools, skills, and knowledge that they could call upon to help them guess what the weather was about to do for a relatively brief amount of time within the limited geographic area around them.
Weather vanes were one common tool used by colonial Americans to help divine the weather. The direction and intensity of the wind can indeed provide a general idea of weather ahead. Breezes from the south typically bring warm temperatures and increased humidity. Winds from the north can mean colder temperatures and drier air. A sudden shift in the wind direction with strong gusts coming from the west may mean a storm is approaching.
Along with wind direction, early Americans also got an idea of what might happen with the weather simply by watching the sky. Over the centuries, folk knowledge from this sky watching was distilled into weather lore, sayings meant to forecast the weather based on these observations of the local sky. Indeed, some weather lore can be explained scientifically, is actually valid, and does provide an idea of what the weather will be for the short-term.
Let’s examine three example sayings (PDF)…
Red sky at night, sailor’s delight
Red sky in the morning, sailor’s warning
Red sky marks where high pressure is located. Dust and soot captured in the high pressure dome scatter more of the sunlight’s red wavelength while regular air molecules scatter sunlight’s blue wavelength. An evening red sky in the west indicates an approaching high pressure bringing calm weather. A red sky in the morning in the east means a high pressure has passed and a low pressure with unsettled weather is likely following behind.
When halo rings the moon
Rain’s approaching soon
At night, high thin cirrostratus clouds can create halos around the moon. These clouds forecast approaching rain.
When clouds look like black smoke
A wise man will put on his cloak
Thick clouds contain a lot of moisture which helps block sunlight and creates an appearance of black smoke in the sky. The moisture in the clouds will often fall as rain, of course, necessitating the need for a cloak to stay dry outdoors.
In the 18th century, many weather sayings once shared through oral tradition were finally recorded in almanacs. The 1700s was a boom time for almanacs and none was perhaps as focused on weather prediction as The Old Farmer’s Almanac, which first appeared in 1792 when George Washington was president.
Robert B. Thomas, The Old Farmer’s Almanac original publisher, created long-term weather forecasts based on a theory developed by Galileo in the 1600s. Galileo and Thomas believed that an 11-year cycle of sunspots influenced the Earth’s climate and weather. To this day, science has not ruled out a connection although sunspot impact on weather is thought to be relatively minor. Nevertheless, a farmer who wanted to know the best day to plant a certain crop and if that day would have good weather consulted The Old Farmer’s Almanac.
The last tool available to 18th century weather prognosticators was the barometer, which measures atmospheric pressure. Generally speaking, a rising barometer means high pressure is approaching and thus good weather is likely ahead while a falling barometer means low pressure is on the way and so is bad weather. While they were over 100-years-old by his time, it does not appear that Washington owned barometer. He definitely owned a thermometer but the many weather observations he recorded in his diaries do not include observations taken on a barometer.
With these primitive tools, skills, and knowledge, weather forecasting in the 18th century was possible but immensely flawed. One could not know anything with certainty. The error rate was substantial to be sure. Forecasting was really little more than making a guess based on some vague general rules of thumb. The advent of telegraphy in 1835 sparked the current age of modern weather forecasting with its collecting and sharing of both observations and data across large distances and its ever-increasing warning times about weather changes.
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