The Chicago National Weather Service Forecast Office went back through the record books to come up with a list of the 20 most significant weather events that occurred in Chicago and surrounding areas from 1900 to 1999. Factors that were considered were number of casualties, amount of property damage, impact on travel and commerce, and uniqueness of the event.

This list is in chronological order. It does not attempt to rank or compare events.

Chicago temperature and rainfall records go back to 1871 and snowfall records go back to 1886. Note that the official weather observatory was downtown or at the University of Chicago until 1942 when Midway Airport became the official Chicago observing site. O’Hare Airport became the official Chicago observation site in 1980. Temperature records can vary from downtown or lakeside locations to the inland airport sites. Both downtown/lakefront and inland temperatures are given for comparison when available.

The Winter of 1903-1904
The coldest winter on record. Temperatures were taken downtown. It was even colder in outlying areas. The winter of 1903-1904 was also the 7th snowiest winter on record with 59.5 inches.

Bitter Cold January, 1912
The second coldest January on record with an average temperature of 11.9. The temperatures were taken downtown. It was even colder inland. (average temperature at Aurora was 8.9) There was a record stretch of 10 days in a row with minimums below zero. There were 13 days below zero for the month.

Late July Heat Wave in 1916
July 26 through July 30, 1916 was one of the most oppressive periods of heat and humidity ever in Chicago, rivaling the heat wave of mid July 1995. Minimum temperatures were in the 80s for 5 consecutive nights, the longest such string in Chicago history. Warm minimum temperatures are an indication of very high humidity. Here are the high and low temperatures for each day. July 26 89/80, July 27 100/82, July 28 97/84, July 29 96/85, July 30 102/84.

Snowfall of January, 1918
The 42.5 inches of snow that fell was a monthly snowfall record. This total included a 14.9 inch snowstorm on the 6th and 7th, followed a week later by a 9.9 inch snow on the 11th and 12th. January, 1918 was part of the 6th snowiest winter ever with 64.1 inches for the season. It was cold, too. Temperatures stayed below freezing from December 28 to January 24, 28 straight days.

March 28, 1920 Tornado Outbreak
Twenty eight people were killed and 400 were injured. There was over $2.5 million (1920 dollars) in damage. There were at least four Chicago area tornadoes. An F3 struck near Elgin. Another tornado occurred from near Channahon to Lockport. It touched down again in Maywood, causing F4 damage. An F2 tornado struck the southwest side of Chicago near Midway. This was the third worst tornado disaster in Chicago history, in terms of casualties.

1930s Dust Bowl Summers
A series of hot dry summers occurred in the early and mid 1930s. June of 1933 was the hottest June on record for Chicago. The summer of 1936 was the third driest on record with only 5.54 inches of rain falling in June, July and August. In the official Chicago record books, the summers of 1934 and 1936 had above normal temperatures but didn't appear to be extremely hot. But these were lakefront temperatures. Inland records from Rockford, Midway and Aurora tell a different story. Twenty five of Rockford's daily record maximum temperatures for the months of May, June, July and August were set in 1934 and were still standing as of 2000. On May 31 it was 104 at Midway, the earliest 100 temperature recorded at any Chicago area location. Chicago's official all-time high temperature of 105 (University of Chicago) was set July 24 1934. It was 109 at Midway, the highest temperature ever recorded at a Chicago location (but Midway was not the official observatory for Chicago in 1934). July of 1936 produced the longest period of scorching heat ever in northeast Illinois. July 6 through 14 1936 there were nine days in a row over 100 at Rockford (all records that still stand) and eight 100s in a row at Midway. The hottest day ever in much of northeast Illinois was July 14 1936. The high temperatures were 112 at Rockford, 111 at Aurora and 104 at Midway.

Seiche of 1954
June 26, 1954, under calm winds and a bright sunny sky, a killer wave rose suddenly from a placid Lake Michigan, sweeping eight unsuspecting fishermen off a breakwater to their deaths.  The water level at Montrose harbor surged more than 10 feet within a few minutes. The seiche was caused by an earlier squall on the lake.

Heavy Rain and Flood of October 1954
12.06 inches of rain fell in October, 1954. That set a record for the month of October. Most of the rain fell in a one week period from the 3rd through the 10th. In Chicago, 3.95 inches fell on the 3rd, 2.27 on the 9th, and 3.94 on the 10th. Elsewhere in northeast Illinois, on the 9th through the 11th 12.1 inches fell at Waterman in DeKalb County and 10.6 inches fell at Aurora. New record crests were established at 24 river gaging stations in northeast Illinois. Flood damage was estimated at 25 million dollars in Chicago and the suburbs.

The Hot Summer of 1955
There were 4 consecutive hot summers beginning in 1952. The heat peaked in 1955, the all-time warmest summer (1952 was the 11th warmest, 1953 was 6th and 1954 was 8th). July 1955 was the warmest month on record with an average temperature of 81.3 . Summer of 1955 had 46 days with a temperature of 90 or greater, including a record 11 in a row from July 26 through August 5. (The summers of 1953 and 1954 also had 11 straight days of 90 weather) This period also had 10 straight minimum temperatures of 75 or greater. Although dew point records aren't readily available, this had to be the longest period of very oppressive heat and humidity in Chicago history.

The Big Snow of January 26-27, 1967
Chicago’s all-time record snowfall of 23.0 inches was established. The snow began on a Thursday morning and didn't let up until the next day. The city of Chicago, including O’Hare Airport, was shut down for several days. An estimated 20,000 cars and 500 buses were stranded on roads everywhere, hampering snow removal efforts. This weather event probably had the greatest impact on the most people in Chicago’s history.

The Tornado Outbreak of April 21, 1967
F4 tornadoes struck Belvidere, Lake Zurich, and Oak Lawn. The twisters left 58 dead, 1100 injured and $100 million in damage. Many of the deaths in Belvidere occurred when the tornado struck the high school while students boarded buses in the parking lot. The Oak Lawn tornado struck the busy intersection of Southwest Highway and 95th street at rush hour, tossing cars and buses. A roller skating rink and high school were also hit. This was the most violent and destructive weather event to occur in northeast Illinois this century.

The Winters of 1976-77 1977-78 and 1978-79
Back to back to back brutal winters occurred in the late 1970s. These were three of the five coldest winters on record. 1976-1977 had 54.1 inches of snow and was the 3rd coldest winter ever. January 1977 was the coldest January on record with an average temperature of 10.1. There were 12 days below zero in January 1977. December 28 1976 to February 8 1977 has the distinction of being the longest continuous string of sub-freezing weather in Chicago history, 43 days. Winter 1977-1978 was the 5th coldest. The 82.3 inches of snow that fell was the 2nd highest seasonal total. Winter 1978-1979 was the 2nd coldest. The 89.7 inches of snow that fell is the all-time season record. One of Chicago's worst blizzards occurred January 12th-14th 1979. The storm total was 20.3 inches of snow. Roofs collapsed from the weight of the snow, people fought over parking spaces and a mayor lost his job.

Bitter Cold Christmas 1983
From December 22 through 25, 1983 the temperature plunged below zero for 100 consecutive hours, a record. It was the coldest Christmas ever in Chicago. December 24th had a low of -25 and a high of -11, an average of -18, making it the coldest day in Chicago history.

Record Cold January 20, 1985
The temperature went down to -27, and a wind chill of -93 was recorded. This is the all-time coldest temperature for Chicago.

Heavy Rain and Flood of August, 1987
Heavy rain fell from August 13th through the 16th. Rain totals were 2.86 on the 12th,  6.49 on the 14th,  0.59 on the 15th,  and 2.90 on the 16th & a 4 day total of over a foot. The 24 hour total of 9.35 inches on August 13th and 14th is the record for Chicago. The total for the month was 17.10 inches. The rain caused flooding in Chicago and the northwest suburbs. O’Hare airport was an island as roads and expressways were under water. Some 15,000 buildings were affected by flooding in Cook and DuPage counties.

The Heat and Drought of the Summer of 1988
There were 47 days with temperatures in the 90s and 7 days in the 100s, both records. Drought lead to lower humidity and lower minimum temperatures than other hot summers. So, despite all the 90 and 100 degree days, 1988 ended up only the 9th warmest summer.

Plainfield Tornado August 28, 1990
A violent tornado touched down near Oswego and ended in Joliet. The path was 16 miles long and as much as quarter mile wide. 29 people were killed, 350 were injured and the tornado caused $165 million in damage. It was the only F5 tornado ever to occur in the Chicago metro area. 

The Heat Wave of July 12-16, 1995
Heat 583 people died in the mid July heat wave, making this the deadliest weather event of the century. Humidity was extremely high with dew point temperatures in the upper 70s to lower 80s. The hottest day was July 13. The high of 104 at O’Hare (official Chicago observatory) was the second highest official temperature in Chicago (the record is 105 July 26 1934). The temperature reached 106 at Midway and 103 at Meigs Field. The heat index peaked at 119 at O’Hare and 125 at Midway. This was probably the most intense combination of heat and humidity ever in Chicago. The summer of 1995 was the second warmest on record.

The Flood of July 17 and 18, 1996
16.91 inches of rain fell in Aurora in 24 hours, breaking the state record. More than 5 inches of rain fell over a large swath from Rockford to Aurora to Joliet to the south side of Chicago. Almost continuous lightning occurred through much of the night of the 17th as wave after wave of thunderstorms rolled through. Travel was nearly impossible on the 18th over the southwest suburbs with I-55 closed in 2 places, I-88 closed in one spot, many major roads closed, and the Burlington Northern line shut down.