Indiana Climate – Sep 2026September 2026 Update

Novarupta (Katmai) eruption

The largest volcanic eruption anywhere in the world in the 20th century - 13 km3 of magma, about thirty times the 1980 Mount St. Helens eruption - at Novarupta in Alaska on 6-8 June 1912. Ash reached 100,000 ft and cooled the Northern Hemisphere by roughly 0.3°C over 1912-13. Unlike a tropical eruption such as Pinatubo, a high-latitude eruption's haze stays in its own hemisphere, so it did little to the Southern Hemisphere.

Smithsonian Global Volcanism Program, Alaska Volcano Observatory, National Park Service, Oman et al. 2005

The Great Flood of 1913 (Indiana)

Indianapolis floodwaters reached 19.5ft above flood stage; ~7,000 families lost homes. Remains the flood of record for many Indiana communities over a century later, and led directly to the Ohio Conservancy Act.

Indiana Magazine of History (IU)

Post-WWII industrial expansion begins

After the Second World War, coal and oil use grew rapidly across Europe, North America and the Soviet Union. Global sulphur dioxide emissions rose from about 30 to about 130 million tonnes a year by 1980, and the sulphate haze they formed masked part of the greenhouse warming underneath - the effect known as 'global dimming'.

Klimont et al. 2013

The 1950s drought

1953 was Indiana's 2nd-driest year (783 mm, 23% below its 1961-90 average) and also its highest heatwave-day count on record at 31.8.

NOAA Drought.gov, NOAA Climate Program Office, Texas Water Development Board

The 1962-66 Northeast drought

1963 was Indiana's driest year in this site's 1950-2025 record - 739 mm, 28% below its 1961-90 average. It was not one dry year but five: 1962-66 as a whole averaged 12% below that baseline. This is the western edge of a drought centred on New England and the Mid-Atlantic, and it peaked a couple of years earlier here than on the coast.

USGS, Seager et al. 2012, NYC Emergency Management

Agung eruption

Agung's eruption in Bali put a veil of sulphate haze into the stratosphere that cooled global temperature by about 0.3°C over 1963-66.

Smithsonian Global Volcanism Program, NOAA Global Monitoring Laboratory

US Clean Air Act

The 1970 Clean Air Act set strict national standards for sulphur dioxide and particulates, and American skies got measurably cleaner over the decades that followed. There is a climate sting in that success: sulphate aerosols reflect sunlight, so removing them removed a cooling effect that had been partly masking greenhouse warming. Measured here, Indiana averaged +0.94°C warmer across 2006-2025 than across the two decades before the Act, 1951-1970, against a median of +1.09°C across the 49 states whose records reach back that far. Every one of them warmed. The range runs from +0.66°C in Oklahoma to +1.67°C in Alaska, so the question a state's own chart answers is not whether it warmed, but by how much.

US EPA

The 1973-74 La Niña

The strongest La Niña of the 1950-present record, part of a multi-year cool phase that also included a second, separate La Niña in 1975-76.

ONI -2.0°C · RONI -1.9°C

NOAA CPCENSO Tracker

The 1976-77 drought

1976 was Indiana's 3rd-driest year on record here - 828 mm, 19% below its 1961-90 average.

USGS, US GAO, USGS Water Data Labs

The cold winters of 1976-79

1979 is Indiana's 2nd-coldest year in this site's 1950-2025 record. Its first months were the end of the winter of 1978-79, the coldest on record for the contiguous United States and the third brutal winter in a row across the Midwest.

Illinois State Water Survey, Missouri Climate Center, Monthly Weather Review (1978), Wikipedia

Pacific Decadal Oscillation flips to a warm phase

The Pacific Decadal Oscillation is a North Pacific pattern, and its influence on this side of the country is weak and indirect - mostly through how it nudges the winter jet stream downstream. Its 1976-77 flip marks a genuine shift in Pacific-basin climate, but for eastern states the Atlantic Multidecadal Oscillation is the ocean cycle that matters more.

Learn more →

Global SO2 emissions peak

Global sulphur dioxide emissions peak at about 130 million tonnes a year, then begin a long decline as Europe, North America and Japan clean up their air. As the aerosol mask thins, the rate of global warming picks up through the 1980s.

Klimont et al. 2013

El Chichón eruption

A sulphur-rich eruption in Mexico whose aerosol cloud stayed in the stratosphere for more than two years, cooling the Northern Hemisphere by about 0.2°C.

Smithsonian Global Volcanism Program

1982-83 El Niño

El Niño has only a weak pull on Indiana's winter rainfall - it is not one of the seven states where ENSO reliably moves it. In 1982-83 Indiana's winter rainfall was close to its 1961-90 average (+3%), with temperatures +3.8°C. On NOAA's RONI index, which strips out background ocean warming, this is the strongest El Niño since 1950.

ONI +2.1°C · RONI +2.4°C

NOAA CPC, NOAA CPC (2)ENSO Tracker

1988 Midwest drought / Yellowstone fires

1988 was Indiana's 6th-driest year (870 mm, 15% below its 1961-90 average) with 17.9 heatwave days, its 4th-highest.

NOAA

Daytime warming catches up with the night-led pattern

Across 1961-90, 81% of the world's land saw nights warming faster than days. Across 1991-2020 the pattern reversed: 70% saw days warming faster, as the industrial haze that had been dimming daytime sunshine was cleaned up. The study compares two fixed thirty-year windows; measured as a turning point, this site's own global series turns around 1982.

Zhong et al. 2023

1990-91: mild winters and warm years

1990 is Indiana's 11th-warmest year in this site's 1950-2025 record, and 1991 its 7th-warmest. Mild winters did most of it: January-February 1990 was the warmest start to a year the contiguous US had recorded, a record that stood until 1998.

News & Record / AP (1991), NOAA NCEI

Mount Pinatubo erupts

Pinatubo's cooling is only faintly visible in Indiana's own record. 1993, two years after the June 1991 eruption, ranks 21st-coldest of the 76 years there, though 1996, 1997 and 2014 have since been colder. A single large eruption can hold temperatures down for two or three years; it cannot reverse the trend.

Learn more →

Atlantic Multidecadal Oscillation flips to a warm phase

The Atlantic Multidecadal Oscillation flipped to a warm phase in 1995. Atlantic hurricanes reach this far inland mostly as remnants - Helene's floods in east Tennessee in 2024 among them - and warm AMO phases have also been linked to more frequent drought across the central United States. It is a natural cycle of roughly 60-70 years, so it shifts the baseline rather than driving the long-term trend.

Learn more →

1997-98 El Niño

In 1997-98 Indiana's winter rainfall was close to its 1961-90 average (-7%), with temperatures +4.5°C - though ENSO's pull on rainfall here is weak. It is often treated as the textbook strong El Niño.

ONI +2.4°C · RONI +2.3°C

NOAA CPC, NOAA NCEIENSO Tracker

Pacific Decadal Oscillation flips back to a cool phase

The Pacific Decadal Oscillation returned to a cool phase around 1998-99. Its direct effects are western - drier conditions across the south-west, changes in North Pacific fisheries - and its influence on this side of the country is weak and indirect. The Atlantic Multidecadal Oscillation, which flipped warm in 1995, is the ocean cycle with more bearing on eastern weather.

Learn more →

The Evansville tornado, November 2005

In the early hours of 6 November 2005 an F3 tornado crossed the Ohio River and tracked 41 miles through the Evansville area. It killed 25 people - 20 of them in the Eastbrook Mobile Home Park - and injured more than 200. It was Indiana's deadliest tornado since the 1974 Super Outbreak.

NWS Paducah, NOAA NCEI Storm Events

Start of the sustained rise in US heatwave frequency

Indiana's own Heatwave Days (WSDI) count rose from a 1961-90 average of 5.4 days a year to 8.6 in 2016-25 - a clear rise, though more moderate than the 2.4x averaged across the 50 states.

World Bank CCKP (CCKP), NOAA Climate at a Glance

The floods of 2011

2011 is Indiana's wettest year in this site's 1950-2025 record - 1,402 mm, 37% above its 1961-90 average, beating a mark set back in 1950. Evansville took 11.77 inches in April alone, within a hundredth of an inch of its wettest April ever.

SIR 2014-5058, NOAA/NWS, NWS Paducah

The 2012 drought and heat

Indiana recorded 28.9 heatwave days in 2012, its 2nd-highest on record here, alongside its 2nd-warmest year and its 5th-driest year (859 mm).

NOAA NCEI, Summer 2012 Drought Update, NOAA NCEI, Drought

Post-2013 acceleration in US temperatures

5 of Indiana's ten warmest years on record have occurred since 2013 - fewer than in most states - but 7 of the ten have come since 2000, with 2024 the warmest of all. The acceleration is clear in Indiana's data; its year-to-year swings are simply wide enough to spread the warmest years further apart than the national mean does.

NOAA Climate at a Glance

The polar-vortex winter of 2013-14

2014 is Indiana's 3rd-coldest year in this site's 1950-2025 record - its coldest since 1979. In early January 2014 the polar vortex slipped south and Arctic air spread across most of the country, and the cold returned in waves into March.

Wikipedia, CBS NewsPolar Vortex Tracker

2015-16 El Niño

In 2015-16 Indiana's winter rainfall ran +30% against the 1961-90 average, with temperatures +3.9°C - though ENSO's pull on rainfall here is weak. By the raw ONI index it was the strongest El Niño ever measured - a reminder that a strong index does not guarantee a strong local outcome.

ONI +2.6°C · RONI +2.3°C

NOAA CPCENSO Tracker

2015-2025: the eleven warmest years on record

Globally, the eleven warmest years on record have all happened since 2015. In Indiana the pattern is weaker: only five of its eleven warmest fall in that span, with 2012, 2006, 1998, 1991, 1990 and 1953 outside it. Its warmest year is 2024. The warming is in Indiana's record; it simply arrives in a different order.

Learn more →

Low-sulphur shipping fuel rule (IMO 2020)

New international shipping rules cut the sulphur allowed in ship fuel from 3.5% to 0.5% almost overnight, removing about 8 million tonnes of sulphur dioxide a year. With less sulphate haze over the oceans, it may have added around 0.1°C of warming by 2023-24.

Gettelman et al. 2024

2023-24 El Niño

A strong El Niño arriving on top of long-term greenhouse warming, with the cut in shipping sulphur from the 2020 fuel rule adding a little more. Together they produced the record global temperatures of 2023 and 2024.

ONI +2.0°C · RONI +1.4°C

NOAA CPCENSO Tracker