Overview

• The fire started during the evening of October 8th, 1871 on the property of Patrick and Catherine O’Leary at 137 DeKoven Street on what was then the southwest side of Chicago, but quickly spread northeastward into the main business district and the heart of the city.

• The fire ended on the morning of October 10th, roughly 36 hours after it had started, after rain had moved in and assisted firefighters with putting the blaze out.

• The fire inflicted devastating losses on both the physical property and the population of the city of Chicago:
  • Estimated 300 fatalities
  • Approximately 100,000 left homeless (about 31% of Chicago’s population at the time)
  • Roughly 2,124 acres (3.3 square miles) of the city burned
  • Approximately 17,500 buildings destroyed
  • Estimated $222 million in damage. When accounting for inflation, this would equate to roughly $5 billion in 2021.

• The Great Chicago Fire was just one of numerous large fires that broke out across the Midwestern U.S. during early October 1871. Other large fires occurred in Indiana, Iowa, Michigan, and Wisconsin. The most notable among these fires was the Peshtigo Fire, which burned 1.5 million acres across northeastern Wisconsin and the northern peninsula of Michigan and caused at least 1,200 fatalities, and to this day is the deadliest fire in U.S. history.

• Official weather observations for the city of Chicago started being taken on October 15th, 1870 at 181 W Washington St. soon after the U.S. Weather Bureau (precursor to the National Weather Service) was signed into existence as part of the Army Signal Corps in 1870. However, this station had to be abandoned on October 8th, 1871 due to the Great Chicago Fire, and all of the records from that station ended up being lost in the fire. Regular observations started being taken again at a different location in the city on October 16th, 1871 and have been taken on every single day up to the present date since then (albeit at different observation sites within the city).

• Prior to the establishment of official NWS observation programs, daily weather observations were recorded at U.S. Army forts. The Smithsonian Institution and the U.S. Department of Agriculture also managed volunteer observer networks that allowed for members of the general public to take and record weather observations. Early weather records from over 50 of these sites were retrieved from NOAA's National Centers for Environmental Information (NCEI) and were utilized for the creation of this web page.

Weather Prior to the Fire
 

The Months Leading Up to the Fire

While there were plenty of rainy periods during the first half of 1871, rainfall quickly became more scarce in the latter half of summer and into the first half of autumn for both Chicago and other areas across the Midwest. For Chicago specifically, the relative lack of rainfall from July through early October caused annual precipitation totals to trend from slightly above average to well below average. Here are a couple of statistics to put the dryness seen in the months leading up to the Great Chicago Fire into perspective:

• In the 3-month period leading up to the fire (July 7 - October 8), only 3.55 inches of precipitation were recorded. This was almost 8 inches below the average amount of precipitation that is typically seen over this 3-month period, and as of 2021, this was the 2nd driest stretch from July 7th through October 8th on record (the driest took place in 1939, when 3.31 inches of precipitation were recorded).
• The month of September on its own was exceptionally dry. As of 2021, it was the 8th driest September on record for Chicago with only 0.74 inches of precipitation recorded during the entire month.
• Only 3 days of the month of September saw measurable precipitation (the 15th, 16th, and 28th). As of 2021, there were only 4 Septembers that had fewer dates with measurable precipitation: September of 1979 had only 1 day with measurable precipitation and the Septembers of 1897, 2004, and 2017 each had only 2 days with measurable precipitation.

The lack of rainfall helped intensify drought conditions across much of the Midwest by the end of September. Vegetation dried out and turned much of the region into a tinderbox where wildfires could ignite and spread very easily if sufficiently dry and windy weather conditions could be realized.

The Week Leading Up to the Fire

The first week of October unfortunately saw these dry and windy conditions take place. From September 29th through October 8th, Chicago saw no precipitation at all. Temperatures during this time frame were generally above normal with most high temperatures reaching the 70s or 80s. Dew points generally ranged between 30 and 50 degrees. Winds during this time frame were generally pretty breezy, gusting to about 15 to 25 mph on most days. Similar weather conditions were seen across much of the rest of the Midwest, where fires began breaking out in rapid succession. Several weather observers across the Midwest reported haze and dense smoke from wildfires that had broken out across the region in their weather reports. However, the worst was still to come...

Weather During the Fire

October 8th

Out of all the warm, dry, and windy days seen in early October 1871, October 8th was by far the most favorable for the spread of fires. Temperatures were very warm for early October with high temperatures in the low to mid 80s across most of northern Illinois, likely after a warm front had tracked through. The weather observer in Aurora, IL had reported that relative humidity ranged from around 35% to 40% during the afternoon and evening. While these humidity values were not particularly favorable for fires to start and spread, they were sufficient when taking into account how dry the vegetation across the area was and that a large percentage of buildings in Chicago were made of wood.

A strong low pressure system moving across the Great Plains was responsible for producing strong winds across the Midwest on October 8th with weather observers in the region estimating that southwest winds peaked at around 35 to 45 mph, including within the city of Chicago. Winds this strong would ensure that any fires that ignited would spread rapidly, and this unfortunately turned out to be the case with the Great Chicago Fire when it broke out later that evening.

Official U.S. Signal Service weather map from the afternoon of October 8, 1871	Digitized surface analysis map from the afternoon of October 8, 1871 based on weather observations taken by volunteer observers and the U.S. Army

October 9th

The day after the fire broke out was another another warm and windy day. High temperatures peaked at in the upper 70s at most observation sites in and near northern Illinois, but it was likely warmer in the heart of the city where the fire was raging. Winds shifted to become more southerly throughout the course of the day but were still gusting to around 35 to 45 mph. The relative humidity had increased slightly during the overnight and morning hours when temperatures cooled before falling again to around 40% by mid-afternoon.

Fortunately, relief would arrive later in the day. The aforementioned low pressure system had moved across the Midwest throughout the day, bringing along a cold front with it. This cold front would reach the Chicago area sometime during the late afternoon or evening and bring relief in the form of rain and cooler temperatures. While the total amount of rain that was received likely wasn't significant (the weather observer in Evanston, IL had reported a total of 0.10" of rainfall the following morning), every drop still helped to combat the fire. Winds shifted to become westerly behind the cold front and had fortunately weakened after the cold front had passed through.

Official U.S. Signal Service weather map from the afternoon of October 9, 1871. Note that there is no observation in Chicago because the weather station there had to be abandoned due to the fire.	Digitized surface analysis map from the afternoon of October 9, 1871 based on weather observations taken by volunteer observers and the U.S. Army

October 10th

The rain eventually ceased sometime on the morning of October 10th. Temperatures had fallen significantly behind the cold front, and afternoon high temperatures didn't even break 50 degrees at some observation sites in northern Illinois. While drier air also moved in behind the cold front, the relative humidity increased to around 60% by around 7 AM. Winds had remained gentle throughout the morning as well. All of these weather conditions assisted greatly with putting the fire out, which was fully extinguished during the morning of October 10th.

Official U.S. Signal Service weather map from the afternoon of October 10, 1871	Digitized surface analysis map from the morning of October 10, 1871 based on weather observations taken by volunteer observers and the U.S. Army

Modern NWS Fire Weather Program

Overview

Since the 1871 Great Chicago Fire, much has evolved with monitoring and predicting fires, and this includes analysis and forecasts of the weather conditions supportive of fire (often referred to as “fire weather”). Since 1914, National Weather Service meteorologists have worked with fire control specialists from other agencies in a supporting role toward efforts to prevent, suppress, or manage wildfires. 

NWS fire weather forecast services include:

• Monitoring observations of fire weather conditions such as wind, humidity, temperature, precipitation, and fuel conditions (vegetation dryness)

• Providing routine forecasts of fire weather conditions over the coming days, and issuing Fire Weather Watches and Red Flag Warnings as necessary

• Receiving requests from partner agencies for site-specific fire suppression efforts, such as prescribed burns, or for partners attempting to contain wildfires

• At times, deploying specially-trained meteorologists known as Incident Meteorologists (IMETs) to the incident command at a fire to support frontline firefighting efforts.

General NWS fire weather forecast information can be found on the NWS Fire Weather page.

NWS Chicago Fire Weather Services

Meteorologists at NWS Chicago provide fire weather forecasts, warnings, and consultation services to local, state, and federal government agencies across northern Illinois and northwest Indiana. The federal agencies we work with are the Indiana Dunes National Park, the Midewin National Tallgrass Prairie, and FermiLab.

Routine fire weather text forecasts are issued three times a day during the spring and autumn fire seasons and once a day in other seasons. Graphical fire weather forecasts are also provided in a gridded, digitized format as part of the National Digital Forecast Database (NDFD).  

When severe fire weather conditions are forecast, the NWS will coordinate with area land management agencies for the issuance of a Red Flag Warning. While intended for primarily land managers, this product also is often highly visible by other decision makers and the public, as we communicate it on our web page and social media platforms. This warning signifies upcoming weather and fuel conditions where burning is extremely discouraged. Communities may institute burn bans during these warnings. Prior to a Red Flag Warning, a Fire Weather Watch may be issued when there is increasing potential of severe fire weather conditions.

Red Flag Warnings & Fire Weather Watches

NWS Chicago prepares special site-specific fire weather forecasts on demand. These forecasts, known as “spot forecasts”, are for partner agencies who are conducting a prescribed burn. They may also be prepared to assist attempts to control a wildfire. These are very detailed forecasts of parameters relevant to fire spread and containment for the location of the fire, with a forecaster discussion that communicates additional details and forecaster confidence.

More on the fire weather forecast program can be found on our NWS Chicago Fire Weather web page.

Other NWS Fire Weather Services

Specially trained NWS meteorologists called Incident Meteorologists (IMETs) provide site-specific weather forecasts for wildfires of all sizes. When requested by other government agencies helping with firefighting, an IMET is deployed with specialized equipment to assist fire crew safety, provide tactical support to the fire management team, and provide weather forecasts to the Fire Behavior Analyst. The forecast evolution of fire weather conditions is essential to incident commanders to make their best decisions to contain wildfires and keep their personnel safe. Special training in mesoscale to microscale forecasting, fire behavior, and fire operations makes these IMETs key members of fire management teams.

The NWS Storm Prediction Center issues national scale fire weather outlook forecasts. These forecasts depict areas where elevated, critical, or extreme fire danger are predicted, and also include a technical discussion.

For more on IMETs, see this "A Day in the Life of an IMET" article.

Outreach

Informing the public on the forecast of dangerous fire weather conditions is highly important ahead of windy, dry, and warm times, but preparedness beforehand is also key. NWS offices will share preparedness information, especially in those locations that commonly see damaging, large fires, such as the western United States. This also includes reminders on how to use heightened safety when burning outside.

Fire weather outreach examples

For more on wildfire safety, see the NWS Wildfire Safety page as well as this Red Cross Wildfire Safety Checklist. 

In Summary

The partnerships between the NWS and government agencies that prevent, suppress, or manage fires have been critical to ensuring advanced notice of weather conditions favorable for rapid fire growth, as well as supporting efforts for battling the inevitable wildfires that do develop. Additionally, the advance of technology, including satellite, observational networks, computer modeling known as numerical weather prediction, and information flow to users and the public, has helped with more accurate and quickly communicated forecast information. Such partnerships and advances go a long way toward ensuring that a fire like the Great Chicago Fire and its associated impacts do not reoccur.