US Upper Midwest 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

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

1951: a cold, wet year and the Great Flood

1951 is Iowa's coldest year in this site's 1950-2025 record, and it was wet as well - 27% above its 1961-90 average. The same cold, rain-soaked year across the central US produced the Great Flood of 1951 further south and west.

NWS Missouri Basin River Forecast Center, USGS

The summer of 1953

One of the most widespread hot summers in the US record: a top-five heatwave year in 23 states. In the Upper Midwest it is the 2nd-highest heatwave year on record in Iowa, Michigan and Wisconsin.

Northeast Regional Climate Center, LIFE

The 1962-66 drought

Centred on the Northeast, the 1962-66 drought was the longest and most severe on the books there, and New York City's reservoirs fell to about a quarter of capacity. It also reached Michigan, where 1963 is the driest year in this site's 1950-2025 record.

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 cut sulphur dioxide and particulate pollution across the country, and removing those sunlight-reflecting aerosols also removed a cooling effect that had been partly masking greenhouse warming. Across the Upper Midwest, 2006-2025 averaged +1.14°C warmer than the two decades before the Act, 1951-1970.

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 Mississippi flood of 1973

A flood of duration rather than height: 88 consecutive days of flood flow at Vicksburg. Upstream, it reached Iowa.

USGS Professional Paper 937, NWS St. Louis

The 1976-77 drought

A short, intense drought that ran from northern Minnesota to southern California. It reached every state in the Upper Midwest.

USGS, US GAO, USGS Water Data Labs

The cold winters of 1976-79

Three severe winters in a row. January 1977 was probably the coldest month the eastern United States had seen in two centuries - Atlanta's coldest month ever measured - and the winter of 1978-79 was the coldest on record for the contiguous United States. Missouri had its coldest winter on record; Illinois had its coldest January-February, 14°F below normal, with seventeen major winter storms.

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.

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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

The 1980 heat wave and drought

A three-month heat wave that killed at least 1,700 people across the country. In the Upper Midwest it hit Minnesota.

NOAA NCEI Billion-Dollar Disasters, Linda Hall Library, Karl & Quayle 1981

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 usually gives the Upper Midwest a mild, dry winter. 1982-83 was mild, +4.1°C against the 1961-90 average, but rainfall went the other way (+36%). 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

The costliest US natural disaster of its time, and the summer Yellowstone burned. The drought reached every state in the Upper Midwest.

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

Mild winters made 1990 the 7th-warmest year then recorded in the contiguous United States, and the 4th-warmest in the Northeast. January-February 1990 set the national record for those months, which stood until 1998, and 1991 was nearly as warm across much of the East.

News & Record / AP (1991), NOAA NCEI

Mount Pinatubo erupts

Pinatubo's aerosol veil left a clear mark on the Upper Midwest. 1993, two years after the June 1991 eruption, is the region's 12th-coldest year of the 76 on record, though 1996 and 2014 have since been colder. A single large eruption can hold temperatures down for two or three years; it cannot reverse the trend.

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The Great Flood of 1993 (Mississippi River)

The greatest flood on record on the Upper Mississippi, with $36.3bn in losses. In the Upper Midwest it hit Iowa and Minnesota.

NASA Earth Observatory / NWS

Atlantic Multidecadal Oscillation flips to a warm phase

The Atlantic Multidecadal Oscillation flipped to a warm phase in 1995. It is an Atlantic cycle, but its reach is not confined to the coast: a warm AMO alongside a cool Pacific has been tied to more frequent drought across the western and central United States, including the widespread droughts of 1996 and 1999-2002. It is a natural cycle of roughly 60-70 years, so it shifts the baseline rather than driving the long-term trend.

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February 1996 Arctic outbreak, state record colds

An Arctic outbreak that set all-time state record lows in Minnesota (-60°F at Tower) and Wisconsin (-55°F at Couderay). The cold reached every state in the Upper Midwest.

NWS La Crosse

1997-98 El Niño

El Niño usually gives the Upper Midwest a mild, dry winter. 1997-98 was mild, +5.5°C against the 1961-90 average, but rainfall stayed close to normal (+8%). 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.

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2006: a national heat record that lasted six years

2006 was the warmest year ever recorded for the contiguous United States, edging past the 1998 El Niño record. A severe heat wave ran from mid-July into late August, killing at least 225 people; on 17 July all but three states reached 90°F or more, and California's central valley hit 110-115°F. In this site's data 2006 now ranks only 10th warmest nationally.

NOAA NCEI, Science

2008 Iowa flood

9.03in of rain fell statewide over ~2 weeks (normal: 2.45in); Iowa's 4th wettest year on record (43.79in) - distinct mechanism and rivers from the 1993 Great Mississippi Flood.

NOAA NCEI

Start of the sustained rise in US heatwave frequency

Across the four states of the Upper Midwest, Heatwave Days (WSDI) rose from a 1961-90 average of 5.4 days a year to 11.9 in 2016-25 - more than doubling, with every one of them recording more heatwave days than in 1961-90. The four states are closely grouped, from 2.0x to 2.4x.

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

The 2012 drought and heat

A drought that covered about 70% of the country at its July peak. It reached every state in the Upper Midwest.

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

Post-2013 acceleration in US temperatures

Across the four states of the Upper Midwest, an average of 4.8 of each state's ten warmest years have come since 2013, ranging from 4 in Michigan to 6 in Iowa. Every state in the region has at least 7 of its ten warmest since 2000.

NOAA Climate at a Glance

Great Lakes water-level swing, 2013 record low to 2020 record high

Jan 2013 record low (lowest since 1918 records began), followed by 2020 record highs after the region's wettest 60-month period in 120 years - a real, dramatic hydrologic swing documented by NOAA GLERL long-term data.

NOAA GLERL

The polar-vortex winter of 2013-14

In early January 2014 the polar vortex slipped south and Arctic air spread from the Rockies to the Atlantic, affecting more than 200 million people. Chicago fell to -16°F on 6 January, and the cold returned in waves into March. It made 2014 one of the coldest years of recent decades across the Midwest and the South.

Wikipedia, CBS NewsPolar Vortex Tracker

2015-16 El Niño

El Niño usually gives the Upper Midwest a mild, dry winter. 2015-16 was mild, +4.4°C against the 1961-90 average, but rainfall went the other way (+63%). 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. The Upper Midwest follows it only partly: four of its own eleven warmest fall in that span, with 2012, 2006, 2005, 2001, 1999, 1998 and 1987 outside it. Its warmest year is 2024.

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2019: the wettest year on record

The wettest year ever recorded for the Midwest as a whole. In the Upper Midwest it is the wettest year on record in Michigan, Minnesota and Wisconsin.

Wisconsin State Climatology Office / WPR, Midwestern Regional Climate Center, NWS Green Bay

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

The 2020 Midwest derecho

The costliest thunderstorm event ever recorded in the United States: $11.2bn in 14 hours. Iowa took the worst of it.

NWS Des Moines, NASA Earth Observatory

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