US Northern Rockies & Plains Climate – Sep 2026September 2026 Update

The 1910 'Big Burn'

Three million acres burned in two days, and the fire set US fire policy for the next century. In the Northern Rockies & Plains it burned across western Montana.

BAMS, 2013

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

The 1950s drought

Among the most widespread and sustained droughts ever recorded in the US - worse than the Dust Bowl in several states. In the Northern Rockies & Plains it reached Nebraska.

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

1951: a cold, wet year and the Great Flood

1951 is Nebraska's coldest year in this site's 1950-2025 record and its 3rd-wettest, 32% above its 1961-90 average - part of the same cold, rain-soaked year across the central US that produced the Great Flood of 1951 further south.

NWS Missouri Basin River Forecast Center, USGS

The 1952 Northwest drought

A north-western drought, separate from the Southern Plains drought of the same decade. 1952 is the driest year on record in Montana and among the three driest in North and South Dakota.

NOAA NCEI

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

Glacier National Park's glacier retreat

A USGS/Portland State study tracked 39 named glaciers across 4 time points (1966-2015/16): average 39% area loss, some up to 85%. Only 26 of the original named ice bodies remain above the 25-acre 'glacier' threshold.

USGS

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 Northern Rockies & Plains, 2006-2025 averaged +1.00°C warmer than the two decades before the Act, 1951-1970.

US EPA

The 1972 Black Hills flood (Rapid City)

A stationary storm dropped ~15in of rain in ~6 hours; flash flooding (compounded by a dam failure) killed 237+ - the highest flood death toll in SD history and among the deadliest US flash floods ever.

USGS Professional Paper 877

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 Nebraska.

USGS Professional Paper 937, NWS St. Louis

The 1976-77 drought

A short, intense drought that ran from northern Minnesota to southern California. In the Northern Rockies & Plains it reached North Dakota and South Dakota.

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

A warm Pacific Decadal Oscillation pushes the winter storm track north of the northern Rockies and Plains, tending to bring milder winters and lighter snowpack. The 1976-77 flip began about two decades of that phase.

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 usually gives the Northern Rockies & Plains a mild, dry winter. 1982-83 was mild, +3.7°C against the 1961-90 average, but rainfall stayed close to normal (-8%). 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 Northern Rockies & Plains.

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 Northern Rockies & Plains. 1993, two years after the June 1991 eruption, is the region's 4th-coldest year of the 76 on record and no year since has been colder there. 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 Northern Rockies & Plains it reached Nebraska, North Dakota and South Dakota.

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.

Learn more →

1997-98 El Niño

El Niño usually gives the Northern Rockies & Plains a mild, dry winter. 1997-98 was mild, +3.6°C against the 1961-90 average, but rainfall stayed close to normal (+3%). It is often treated as the textbook strong El Niño.

ONI +2.4°C · RONI +2.3°C

NOAA CPC, NOAA NCEIENSO Tracker

The 1997 Red River flood (Grand Forks)

The most severe Red River flood since 1826 - Grand Forks/East Grand Forks evacuated ~90% of their population, the largest US city evacuation since the Civil War at the time. $3.5bn damage.

NOAA CPC

Pacific Decadal Oscillation flips back to a cool phase

The Pacific Decadal Oscillation flipped back to a cool phase around 1998-99, which tends to favour colder, snowier winters across the northern Rockies and Plains.

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Colorado River flow decline / Lake Mead crisis

A decline in the river's flow of which roughly a third to a half is attributable to warming alone, not to reduced precipitation. Wyoming is where much of that water starts: the Green River, the Colorado's largest tributary, rises in its Wind River Range.

Udall & Overpeck 2017

The 2002 Western drought

The sharpest single dry year of the early Southwest megadrought, and Colorado's driest year on record. In the Northern Rockies & Plains it reached Nebraska, South Dakota and Wyoming.

NOAA Drought.gov, NOAA NCEI

2006: a national heat record that lasted six years

The warmest year ever recorded for the contiguous United States at the time - since pushed down to 10th. In the Northern Rockies & Plains it is still a top-five warm year in Montana, Nebraska, North Dakota and South Dakota.

NOAA NCEI, Science

Start of the sustained rise in US heatwave frequency

Across the five states of the Northern Rockies & Plains, Heatwave Days (WSDI) rose from a 1961-90 average of 6.3 days a year to 9.9 in 2016-25 - a rise of 57%, with 4 of the 5 recording more heatwave days than in 1961-90. It is not uniform: Nebraska is at 2.4x, Montana at 1.0x.

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 Northern Rockies & Plains.

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

Post-2013 acceleration in US temperatures

Across the five states of the Northern Rockies & Plains, an average of 4.6 of each state's ten warmest years have come since 2013, ranging from 4 in Montana to 6 in Wyoming. Every state in the region has at least 6 of its ten warmest since 2000.

NOAA Climate at a Glance

2015-16 El Niño

El Niño usually gives the Northern Rockies & Plains a mild, dry winter. 2015-16 was mild, +3.7°C against the 1961-90 average, but rainfall went the other way (+17%). 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 Northern Rockies & Plains follows it only partly: five of its own eleven warmest fall in that span, with 2012, 2006, 1999, 1998, 1987 and 1981 outside it. Its warmest year is 2012.

Learn more →

The 2015 western snow drought

The year 81% of the West's monitored snow sites hit record-low snowpack - driven by warmth, not a shortage of precipitation. In the Northern Rockies & Plains it reached Montana and Wyoming.

Mote et al. 2016, NOAA Drought.gov, USDA

Montana's record-cold February, 2019

February 2019, weeks after a sudden stratospheric warming split the polar vortex, was Montana's coldest February since 1936 - 19.5°F below normal statewide. Great Falls ran nearly 28°F below normal and stayed below freezing for 32 days in a row into early March. It pulled 2019 down to Montana's 12th-coldest year in this site's 1950-2025 record - a rare cold year in a warming decade.

NWS Great Falls, NOAA NCEIPolar Vortex Tracker

March 2019 'bomb cyclone' flooding

A rapidly-intensifying cyclone plus frozen ground and rapid snowmelt produced record Missouri River flooding - $10.8bn regional damage, one of the costliest US inland flood events on record. Nebraska alone: ~$2.7bn in damages to 7,000+ homes.

Weather.com / NOAA

2019: the wettest year on record

The wettest year ever recorded for the Midwest as a whole. In the Northern Rockies & Plains it is the wettest year on record in North Dakota and South Dakota, and the 2nd-wettest in Nebraska.

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. It began in South Dakota.

NWS Des Moines, NASA Earth Observatory

The 2022 Yellowstone flood

A 500-year flood that closed Yellowstone National Park entirely. It hit Montana and Wyoming.

NASA Earth Observatory, WyoFile

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