Caption: U.S. Army Signal Service Weather Map for 7:35 a.m. Eastern Time, October 8, 1871. The wind at Chicago was out of the southwest—the prevailing direction for the month—at 19 mph. Its intensity would only increase later that day as a massive fire swept across the city.
In his 1883 memoir of his days as a riverboat pilot, Life on the Mississippi, Mark Twain wrote, “It is hopeless for the occasional visitor to try to keep up with Chicago—she outgrows his prophecies faster than he can make them. She is always a novelty, for she is never the Chicago you saw when you passed through the last time.”
Twain could have been writing of Chicago in the years after the great fire of 1871, which burned more than 2,000 acres, destroying the city's central business district, including some 1,600 stores, 28 hotels, and 60 churches. The fire killed more than 200 people (a relatively small number for a blaze of such magnitude) and left another 90,000 homeless—nearly one-third of the city's population at the time. Chicago would eventually rebuild and transform itself into a modern city, but only after it was, as the Chicago Tribune put it, “swept by a conflagration which has no parallels in the annals of history, for the quantity of property destroyed, and the utter and almost irremediable ruin which it wrought.”
The great fire started around 9:30 p.m. on October 8, in or near the barn behind the home of Patrick and Catherine O'Leary, at 137 DeKoven Street, just southwest of the Chicago Loop. While legend would have us believe that Mrs. O'Leary's cow began the blaze when it kicked over a lantern, this story was proved to be a fabrication from the mind of Chicago Republican reporter Michael Ahern, who thought it would make for more colorful copy.
What is true is that much of the Upper Midwest, including Chicago, had been experiencing drought conditions in the months leading up to the fire. In reporting on the Chicago fire and other fires that occurred around the same time from the Rocky Mountains to central New York and Pennsylvania, Professor Increase A. Lapham of Milwaukee (who had been instrumental in creating the first national weather service in the United States in 1870, under the auspices of the U.S. Army Signal Service, and served as a civilian assistant to the chief signal officer) noted the fires:
… must be regarded as the effect of meteorological causes. Unusual dryness has pervaded the atmosphere during the past two months; the amount of rain-fall (sic) has been considerably less than the average and the amount of evaporation considerably more. Very little rain has fallen upon most of this extended region since August.
Further evidence of drought conditions is presented by Weather Bureau Professor Henry J. Cox and forecaster John Armington in their 1914 publication The Weather and Climate of Chicago:
A drouth (sic) period of more than ordinary interest to Chicagoans is that covering 22 days, from September 17 to October 8, 1871, just prior to the Great fire. But 0.11 inch of rain fell during the 22 days mentioned, and, indeed, for more than two and a half months previous there had been comparatively little rainfall; and it is undoubtedly because of the extreme dryness of the buildings, due to the drouth, that the fire spread so rapidly.
Measurable amounts of rainfall occurred on only 17 days during the period from July 1 through the start of the fire on October 8, with a total amount of precipitation of only 5.27 inches, a departure of 4.94 inches from the normal for that period.
The official Signal Service weather map issued on the morning of October 8 indicated southwesterly winds at Chicago, with a temperature of 51°F. This map—one of the first issued by the burgeoning weather service since it began publishing daily weather maps on January 1, 1871—offers little in the way of a detailed picture of the synoptic situation on the day the fire broke out. Much more detailed maps, based on a reanalysis, and a more detailed description of the synoptic weather conditions at the time, appear in the article “When the Midwest Burned,” published in the June 1970 issue of Weatherwise. The map for 7:00 a.m. EST on October 8 and shows a developing area of low pressure centered over the southeastern part of what is today South Dakota. A second low, not pictured on the map, was located near Salt Lake City, Utah, with an associated cold front extending to the south. Chicago lay in the warm sector ahead of this cold front, and on the warm side of the stationary front depicted in the map.
As the day progressed, the pressure at Chicago decreased, while the temperature and wind speed increased, as shown in the weather observations from that day (Table 1).
Table 1. Weather observations from October 8, 1871
7:35 a.m. EST
3:35 p.m. EST
11:35 p.m. EST
SW 19 mph
SW 22 mph
SSW 18 mph
The “smoky” weather conditions reported early in the day are likely a reference to another, smaller fire that burned the previous day in Chicago. The smoke from the great fire that broke out that evening would eventually drift eastward, becoming visible to residents in New York and New England.
In his official weather journal, Sgt. James Mackintosh, observer in charge of the Chicago Signal Service station, wrote:
The weather was intensely dry, and the wind blowing from the south-southwest with a velocity of about twenty miles per hour. Accordingly, when by 10 o'clock p.m. the fire had increased instead of diminishing, many people turned out to see it, not from alarm, but simply for the sake of the spectacle. At 10:30 the fire was still confined to two blocks, with a strong hold of only one. The firemen at this time seemed to have a fair chance of checking it, still the burning was so great as to enable one, by the light of it, to read the time on the city clock, one-and-a-half-miles distant. The wind was carrying the sparks right through the center of the city, the line lying only two blocks west of the city hall. Still, no one felt alarmed, except those in the immediate vicinity. I myself was present, and had seen the much larger fire of the previous night checked by the river. By 12 a.m. the fire had increased considerably in area and intensity, but as the wind was south-southwest, and the river ran due north and south, there seemed as yet by little danger for anything beyond the river. Hitherto the fire had been propagated, and with no great velocity, merely by contact with the flames, but toward 1 a.m. the heat of the fire had become so intense as greatly to increase the power of the wind in the immediate neighborhood of the flames. This was especially the case on the east and west of the fire toward the front, the wind blowing straight toward the fire in all directions. Within forty yards of the blaze I estimated the wind blowing from the east toward it at thirty miles per hour. This caused a decided whirling motion in the column of flame and smoke, which was contrary to the hands of a watch.
Mackintosh went on to describe how the fire progressed as the city's firemen tried in vain to keep it in check, ultimately destroying the local Signal Service office, along with all of its instruments and records, despite the attempts of his assistant, Sgt. W.S. Kaufman, to save them:
The observation-office lay right in the path along which the conflagration mowed its first swath, from the southwest through the center of the city to the northwest. I went to the scene of the fire between 10 and 11 p.m., and did not think of the danger until too late. Kaufman was on duty, and saved the most valuable of the instruments, but only for a time. He carried them to his lodgings, which lay nearer the lake, and returned to find all the buildings around the office in a blaze. Thinking himself safe, he went back to his lodgings and went to sleep, and awoke in time to find the flames just upon him.
Mackintosh reunited with Kaufman on October 10, but it was not until the 16th that they were able to take possession of a new office. This did not, however, keep them from resuming their duties, which they did on October 12, upon receipt of new instruments sent by the central office in Washington, D.C., and a new printing press for the issuing of weather maps, sent from New York.
By the time the cold front associated with the advancing low passed over Chicago, during the morning of October 10, the fire had burned itself out. Although rainfall amounts in excess of one inch were reported across the mid-Mississippi Valley with the passage of the frontal system, only about 0.1 inch of rain fell in Chicago, which likely had little effect on the fire.
Contributing Editor SEAN POTTER is a New York-based Certified Consulting Meteorologist (CCM) and science writer with an interest in weather history.