Montana Climate – Sep 2026September 2026 Update

The 1910 'Big Burn'

Western Montana burned alongside northern Idaho in the Big Burn of August 1910, with Taft and other rail towns along the Bitterroot divide destroyed. The fire's political consequence outlasted its smoke: it entrenched total fire suppression as US Forest Service doctrine for most of the following century, a policy now understood to have left western forests carrying far more fuel than they would naturally hold.

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 1952 Northwest drought

1952 is Montana's driest year in this site's 1950-2025 record - 338 mm, 30% below its 1961-90 average. This is a north-western drought, separate from the great 1950s drought of the Southern Plains that ran through the same decade.

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 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, Montana 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

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.

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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 Montana's winter rainfall - it is not one of the seven states where ENSO reliably moves it. In 1982-83 Montana's winter rainfall ran -12% against the 1961-90 average, with temperatures +3.6°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 Montana's 5th-driest year (369 mm, 23% below its 1961-90 average) with 33.8 heatwave days, its 2nd-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

Mount Pinatubo erupts

Pinatubo's aerosol veil left a clear mark on Montana. 1993, two years after the June 1991 eruption, is Montana's 10th-coldest year of the 76 on record, though 1996 has 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. 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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1997-98 El Niño

In 1997-98 Montana's winter rainfall ran -32% against the 1961-90 average, with temperatures +2.8°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, which tends to favour colder, snowier winters across the northern Rockies and Plains.

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2006: a national heat record that lasted six years

2006 is Montana's 5th-warmest year in this site's 1950-2025 record. It was the warmest year ever recorded for the contiguous United States at the time, beating the 1998 El Niño record - and it has since been pushed down to 10th nationally, passed by nine warmer years in under two decades.

NOAA NCEI, Science

Start of the sustained rise in US heatwave frequency

Montana's own Heatwave Days (WSDI) count went from a 1961-90 average of 8.4 days a year to 8.1 in 2016-25 - essentially flat, making it one of only two states where the national rise in heatwave frequency does not show up at all.

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

The 2012 drought and heat

2012 was Montana's 4th-warmest year, but neither exceptionally hot (34th-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 Montana by.

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

Post-2013 acceleration in US temperatures

4 of Montana'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 2015 the warmest of all. The acceleration is clear in Montana'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

2015-16 El Niño

In 2015-16 Montana's winter rainfall ran -11% against the 1961-90 average, with temperatures +3.8°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 Montana the pattern is weaker: only four of its eleven warmest fall in that span, with 2012, 2007, 2006, 1999, 1988, 1987 and 1981 outside it. Its warmest year is 2015. The warming is in Montana's record; it simply arrives in a different order.

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The 2015 western snow drought

For Montana, 2015 was its warmest year on record and its 4th-highest heatwave-day count (24.6 days). The snow drought itself bit hardest west of the Continental Divide, so Montana's 2015 is a warmth record more than a snow one.

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

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 2022 Yellowstone flood

The worst community damage from the June 2022 Yellowstone flood fell on Montana: Gardiner was cut off, Red Lodge flooded, and the road from the park's north entrance was torn away in several places. Montana's 2022 rainfall finished 3% below its 1961-90 average, which is exactly why annual figures are a poor guide to this kind of event - it was days of rain on melting snow, not a wet year.

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