New Hampshire 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

Mount Washington's 231mph wind gust

The fastest surface wind gust ever recorded by a staffed weather station (still the staffed-station record).

Mount Washington Observatory

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 summer of 1953

Between 24 August and 6 September 1953 the north-eastern United States recorded 1,097 readings above 90°F, 546 above 95°F and 129 above 100°F. New York City spent twelve consecutive days in the 90s. At least 59 people died directly of the heat in that fortnight, and 576 across the year - most of the country from the Rockies to the Atlantic was described at the time as suffering its worst heat and drought since the Dust Bowl.

Northeast Regional Climate Center, LIFE

The 1962-66 Northeast drought

1965 was New Hampshire's driest year in this site's 1950-2025 record - 835 mm, 26% below its 1961-90 average. It was not one dry year but five: 1962-66 as a whole averaged 14% below that baseline.

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, New Hampshire averaged +1.33°C warmer across 2006-2025 than across the two decades before the Act, 1951-1970, the 9th-largest rise of the 49 states measured and above their median of +1.09°C. Cleaning the air was right for human health. It also uncovered warming that was already there.

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

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

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 New Hampshire's winter rainfall - it is not one of the seven states where ENSO reliably moves it. In 1982-83 New Hampshire's winter rainfall ran -10% against the 1961-90 average, with temperatures +2.8°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

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 New Hampshire's 13th-warmest year in this site's 1950-2025 record. 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 New Hampshire's own record. 1993, two years after the June 1991 eruption, ranks 23rd-coldest of the 76 years there, though 1997 and 2003 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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Atlantic Multidecadal Oscillation flips to a warm phase

The Atlantic Multidecadal Oscillation flipped to a warm phase in 1995, and for the Northeast its reach is through the Atlantic hurricane season: the warm phase since includes Irene in 2011 and Sandy in 2012. 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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1997-98 El Niño

In 1997-98 New Hampshire's winter rainfall ran +16% against the 1961-90 average, with temperatures +3.5°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

The Ice Storm of 1998

Northern New Hampshire was hit hard by the January 1998 ice storm, with prolonged freezing rain bringing down power lines and trees across the north of the state. The heaviest accretion, and the worst of the damage, was over the border in Maine.

USDA Forest Service

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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The 1999-2002 Eastern drought

2001 was New Hampshire's 2nd-driest year on record here - 886 mm, 21% below its 1961-90 average. It was not one dry year: 2001 and 2002 together averaged 10% below that baseline.

USGS New England Water Science Center, Vermont State Climate Office, NOAA Drought.gov

The hot summer of 2002

2002 gave New Hampshire 12.8 heatwave days, its 5th-highest of the 1950-2025 record, against an annual mean that ranks only 17th-warmest - another summer that does not show in a yearly average.

NOAA NCEI

The October 2005 Northeast floods

October 2005 is still the wettest month ever recorded in Concord, in records going back to 1868 - 14.57 inches. In Alstead an embankment on the Cold River gave way and sent a 20-30 ft wave through the village, destroying 40 homes and killing four of the six New Hampshire deaths. 2005 finished as the state's wettest year in this site's 1950-2025 record, 38% above its 1961-90 average.

USGS, US Army Corps of Engineers

Start of the sustained rise in US heatwave frequency

New Hampshire's own Heatwave Days (WSDI) count rose from a 1961-90 average of 2.6 days a year to 9.6 in 2016-25 - more than a threefold increase, well ahead of the 2.4x averaged across the 50 states.

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

The Northeast's record summer of 2010

2010 gave New Hampshire 16.9 heatwave days, its 2nd-highest of the 1950-2025 record, alongside its 5th-warmest year overall.

NOAA Climate.gov, NOAA NCEI, Northeast Regional Climate Center

2012: the warmest year on record for the contiguous US

2012 is New Hampshire's 3rd-warmest year in this site's 1950-2025 record. Nationally it was the warmest year the contiguous United States had recorded, 3.2°F above the 20th-century average, with a record-warm March that broke more than 15,000 daily records; 19 states set record-warm years.

NOAA Climate.gov, NOAA Climate.gov (2)

Post-2013 acceleration in US temperatures

6 of New Hampshire's ten warmest years on record have occurred since 2013, and 9 of the ten since 2000, with 2024 the warmest of all.

NOAA Climate at a Glance

2015-16 El Niño

In 2015-16 New Hampshire's winter rainfall ran +22% against the 1961-90 average, with temperatures +5.0°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. New Hampshire's own record is a looser fit - six of its eleven warmest fall in that span, with 2012, 2010, 2006, 1999 and 1998 outside it. Its warmest year is 2024.

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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