Utah 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

The 1950s drought

1956 was Utah's 2nd-driest year - 206 mm, 41% below its 1961-90 average.

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

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, Utah averaged +1.09°C warmer across 2006-2025 than across the two decades before the Act, 1951-1970 - exactly the median of 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 Utah's 5th-driest year on record here - 233 mm, 33% below its 1961-90 average.

USGS, US GAO, USGS Water Data Labs

Pacific Decadal Oscillation flips to a warm phase

A warm Pacific Decadal Oscillation tends to bring the Southwest wetter winters, and the two decades after the 1976-77 flip were among the region's wetter spells of the century - which is part of why the drought that followed the flip back in 1998-99 came as such a contrast.

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 Utah's winter rainfall - it is not one of the seven states where ENSO reliably moves it. In 1982-83 Utah's winter rainfall ran +17% against the 1961-90 average, with temperatures +1.3°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

Mount Pinatubo erupts

Pinatubo's aerosol veil left a clear mark on Utah. 1993, two years after the June 1991 eruption, is Utah's 12th-coldest year of the 76 on record and no year since has 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. 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

In 1997-98 Utah's winter rainfall ran +31% against the 1961-90 average, with temperatures +1.2°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 flipped back to a cool phase around 1998-99. Cool phases favour dry winters across the Southwest, and the flip coincides with the start of the megadrought in 2000 - natural variability setting the stage, with warming then deepening it.

Learn more →

Southwest megadrought (2000-2021+)

Utah's 2000-2021 rainfall averaged 5% below its 1961-90 average. The effect on the Great Salt Lake, which reached record lows in 2021 and 2022, was amplified by water withdrawal on top of the shortfall.

Williams et al. 2022

Colorado River flow decline / Lake Mead crisis

Utah sits in the river's Upper Division and contains Lake Powell, the basin's other great reservoir, which fell to record lows alongside Mead from 2021 and came close to the level at which Glen Canyon Dam can no longer generate power. Udall & Overpeck (2017) attribute roughly a third to a half of the flow decline to temperature rather than to reduced precipitation.

Udall & Overpeck 2017

The 2002 Western drought

2002 was Utah's 3rd-driest year on record here - 230 mm, 34% below its 1961-90 average.

NOAA Drought.gov, NOAA NCEI

Start of the sustained rise in US heatwave frequency

Utah's own Heatwave Days (WSDI) count rose from a 1961-90 average of 6.0 days a year to 20.4 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 2012 drought and heat

2012 was Utah's 3rd-warmest year, but neither exceptionally hot (27th-highest for heatwave days) nor exceptionally dry (13th-driest of 76 years). The drought that made 2012 notorious nationally had its worst conditions over the Plains and Corn Belt, and largely passed Utah by.

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

Post-2013 acceleration in US temperatures

8 of Utah's ten warmest years on record have occurred since 2013, and all ten since 2000, with 2025 the warmest of all - a local acceleration closely tracking the national one.

NOAA Climate at a Glance

2015-16 El Niño

In 2015-16 Utah's winter rainfall was close to its 1961-90 average (+4%), with temperatures +0.7°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. Utah follows closely: eight of its own eleven warmest fall in that span, with 2014, 2012 and 2003 outside. Utah's warmest year is 2025.

Learn more →

The West's air gets drier

Utah's relative humidity has fallen 3.9 percentage points comparing 2015-2025 with 1950-2014 - the largest fall of any US state - while its annual temperature rose +1.11°C over the same comparison.

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

The 2015 western snow drought

For Utah, 2015 was its 4th-warmest year, its highest heatwave-day count (38.5 days) and its 5th-lowest snow year of 44.

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

The Hildale and Zion flash floods

On 14 September 2015 slow-moving thunderstorms over south-west Utah sent flash floods down Short Creek in Hildale and through Keyhole Canyon in Zion National Park. Twenty-one people died - 14 from Hildale, most of them in two vans swept away by the flood, and 7 canyoneers in Zion - the deadliest natural disaster in Utah's history.

NOAA NCEI Storm Events, FOX Weather

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

Great Salt Lake's record-low water level, 2022

Reached its lowest recorded level in November 2022. A 2025 peer-reviewed study (Bigalke et al., Geophysical Research Letters) found reduced streamflow explains about two-thirds of the decline, but warming-driven evaporation accounts for the remaining third - without the warming trend, 2022 would NOT have been a record low.

Bigalke et al. 2025

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