Precipitation, Sunshine, Frost and Snow are converted to standard deviations from their own average so they can share an axis with Temperature anomalies.
Metric
Insight
Temperature
10-Yr AverageActual Year
Climate History
38 of 38 events
1910Other
The 1910 'Big Burn'
Three million acres burned in two days, and the fire set US fire policy for the next century. In the Northwest it burned across northern Idaho and into Washington.
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.
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'.
A north-western drought, separate from the Southern Plains drought of the same decade. 1952 is the driest year on record in Washington, the 2nd-driest in Idaho and the 6th-driest in Oregon.
In mid-November 1955 a record-breaking Arctic outbreak swept into the Pacific Northwest before trees had hardened off for winter, killing or damaging large areas of young forest in western Washington. It capped a cold year across the region.
April snowpack declined at 81% of measured western US sites from 1955-2023 (avg ~18% decline); Idaho's state climatologist has documented a clear multi-decade warming/drying trend feeding the Snake River system.
1958 stands out as a warm spike on Pacific Northwest charts. It followed the 1957-58 El Niño, one of the strongest of the 20th century, in a period when the whole north-east Pacific ran unusually warm - fisheries scientists called 1957 'the year of warm water'.
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 Northwest, 2006-2025 averaged +0.87°C warmer than the two decades before the Act, 1951-1970.
The Pacific Decadal Oscillation is this region's own ocean rhythm. Its warm phase gives the Pacific Northwest milder, drier winters and a thinner mountain snowpack, and the 1976-77 flip began about two decades of it - long enough to show in the region's salmon runs, which is how the pattern was first identified.
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.
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.
El Niño usually gives the Northwest a mild, dry winter. 1982-83 was mild, +1.6°C against the 1961-90 average, but rainfall went the other way (+23%). On NOAA's RONI index, which strips out background ocean warming, this is the strongest El Niño since 1950.
November 1985 was the coldest November on record in Seattle, by more than 3°F, with days of sub-freezing temperatures and repeated snow. It ended a cold and dry year across the Pacific Northwest, with rainfall about 30% below the 1961-90 average.
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.
Pinatubo's aerosol veil left a clear mark on the Northwest. 1993, two years after the June 1991 eruption, is the region's 5th-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.
1992 was one of the Pacific Northwest's warmest years, following the 1991-92 El Niño. El Niño winters in the Northwest tend to run warmer and drier than normal, with a thinner mountain snowpack.
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.
El Niño usually gives the Northwest a mild, dry winter. 1997-98 was mild, +1.2°C against the 1961-90 average, but rainfall stayed close to normal (-1%). It is often treated as the textbook strong El Niño.
Pacific Decadal Oscillation flips back to a cool phase
The Pacific Decadal Oscillation flipped back to a cool phase around 1998-99. For the Pacific Northwest a cool phase favours cooler, wetter winters and a deeper mountain snowpack - the opposite of the two decades before.
2004 is Washington's 7th-warmest year in this site's 1950-2025 record. The warmth carried into the winter of 2004-05, when much of the precipitation fell as rain rather than snow; the mountain snowpack finished 3rd-lowest on record and the state declared a drought in 2005.
Start of the sustained rise in US heatwave frequency
Across the three states of the Northwest, Heatwave Days (WSDI) rose from a 1961-90 average of 8.5 days a year to 13.0 in 2016-25 - a rise of 53%, with every one of them recording more heatwave days than in 1961-90. The three states are closely grouped, from 1.3x to 1.7x.
Across the three states of the Northwest, an average of 6.3 of each state's ten warmest years have come since 2013, ranging from 6 in Idaho to 7 in Oregon. Every state in the region has at least 7 of its ten warmest since 2000.
"The Blob": the North Pacific marine heatwave of 2014-16
A vast patch of unusually warm water - nicknamed "the Blob" - spread across the north-east Pacific from late 2013 and lasted into 2016, at times more than 2.5°C above normal. It coincided with the PDO's swing to its warm phase and then the 2015-16 El Niño. Its effects ran through the food web: about 62,000 dead common murres washed ashore from California to Alaska in 2015-16, with total deaths estimated near a million birds - the largest seabird die-off on record.
At 10:37 on 22 March 2014, a rain-soaked hillside above the North Fork Stillaguamish River near Oso, Washington, collapsed. Some 18 million tons of sand, mud and debris crossed the valley at around 40 mph, burying the Steelhead Haven community and State Route 530. It killed 43 people - the deadliest landslide in US history.
El Niño usually gives the Northwest a mild, dry winter. 2015-16 was mild, +1.6°C against the 1961-90 average, but rainfall went the other way (+24%). 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.
Globally, the eleven warmest years on record have all happened since 2015. The Northwest is a looser fit: six of its own eleven warmest fall in that span, with 2014, 2003, 1992, 1987 and 1958 outside it. Its warmest year is 2015.
Washington's largest wildfire season on record, 2015
1,137,664 acres burned (Jun-Sep 2015), amid historic regional drought - the largest Washington fire season on record, called a likely 'harbinger' of future conditions.
The year 81% of the West's monitored snow sites hit record-low snowpack - driven by warmth, not a shortage of precipitation. In the Northwest it reached Idaho and Oregon.
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.
Oregon's most destructive fire season on record - five simultaneous megafires driven by an extreme offshore wind event. A peer-reviewed study (Abatzoglou et al. 2021) found these fires burned more Cascades forest than the previous 36 years combined.
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.
Warm Spell Duration Index (WSDI) - days in a 6+ day run above the local 90th-percentile temperature for that time of year.
Heatwave days per year2015 (Record)10-yr avg
Data: World Bank Climate Change Knowledge Portal (ERA5-derived), aggregated by 4BYO across member states. Refreshed roughly 1-2x/year, ~7-8 months behind present.
Source: NOAA Climate at a Glance — US states & climate regions (tavg, pcp), plus GPCC (Snow, water-equivalent). Anomalies are vs the 1961–1990 baseline. See methodology.
How spring and autumn have shifted in US Northwest. Spring is defined as the date monthly temperatures first rise above the long-term annual mean (7.3°C, from 1950–1979); autumn is the date they fall back below it. Temperature swings 21.0°C peak-to-peak across the year - a classic four-seasons rhythm.
Shifting summer
10 Days Longer
Warm Season
1950–1979 Baseline: 27 Apr → 20 Oct · 176 days
2016–2025 Now: 20 Apr → 22 Oct · 186 days
−7d+2d
JanJFebFMarMAprAMayMJunJJulJAugASepSOctONovNDecD
Spr 7 Days EarlierAut 2 Days Later
baseline avgrecent avgClickTap for decades
1950–19792016–20251950–1979 annual mean
Baseline vs recent monthly temperature climatology. Biggest warming: Aug (+1.9°C).
NOAA Climate at a Glance — regional tavg. Baseline: first 30 yrs on record. Recent: last 10 yrs on record.
The natural climate patterns that measurably shape seasonal temperature or rainfall in the US Northwest, from this site’s own data since 1950 - long-term trends removed, and ENSO’s share taken out before scoring the others, so each is credited only for what it adds.
El Niño / La Niña (ENSO)moderate link
The tropical Pacific’s warm and cool swings - the biggest natural driver of year-to-year climate.
Now: El Niño (strong) · RONI +1.7°C(Jul-Sep 2026)
Forecast - 100% very strong at peak, Sep-Nov, then neutral by Apr-Jun 2027 (NOAA). La Niña from Sep 2027 in SNU’s AI model.
A moderate or strong link for 100% of the places in this group.
Every figure on this page is sourced from official, openly published climate datasets. Anomalies are calculated against the 1961–1990 baseline (temperature) and 1991–2020 (rainfall, sunshine, frost) - see the Methodology & Sources page for the complete dataset list and update calendar.
The US Northwest is warming in line with the rest of the world. The page above shows the latest monthly temperature anomaly versus the 1961-1990 baseline, the long-term annual trend, and the region's rank in the historical record. The headline panel also shows the long-term trend rate per decade and the warmest and coolest years on file.
Which climate drivers affect the weather in the US Northwest?
Measured from seasonal temperature and rainfall in the US Northwest since 1950, with the long-term warming trend removed (and ENSO's own share removed before scoring the other drivers), the climate drivers with a clear effect here are: El Niño / La Niña (ENSO) - a moderate or strong link for 100% of the places in this group; the Pacific-North American pattern (PNA) - a moderate or strong link for 100% of the places in this group; the North Atlantic Oscillation (NAO) - a moderate or strong link for 67% of the places in this group. There are also weaker links to the AO. Their current state is shown in the Climate Drivers section of this page.
What extreme weather affects the US Northwest?
NOAA's Storm Events Database recorded 47 damaging weather events in the US Northwest in 2025 - storms, floods, heat, drought and wildfires that killed or injured anyone or did $1M or more of damage - against an average of 38 a year in 2016-2025, with 10 deaths. The deadliest since 1996 was 2021 Pacific Northwest heat dome (26 June 2021, Oregon), which killed 118. GDACS, the UN and European Commission's disaster alert system, issued 0 Major (Red) and 0 Severe (Orange) alerts for the US Northwest in the last 12 months. Live alerts are on this page and on the Extreme Weather tracker.
Where does the climate data for the US Northwest come from?
Climate data for the US Northwest comes from authoritative climate datasets including national meteorological services and peer-reviewed reanalyses, refreshed every month, when the upstream temperature and rainfall data are refreshed.
What is the climate baseline used on this page?
Anomalies on this page are calculated against the 1961-1990 climatological baseline, which is the standard reference period used by the Met Office, NOAA, IPCC and most national climate services. Some panels also show the source-native 1901-2000 (NOAA) or 1991-2020 (WMO) baselines for verification. See Methodology & Sources for the full reference.
Which areas does the US Northwest climate data cover?
The US Northwest climate profile covers Washington, Oregon, Idaho and surrounding areas. NOAA Northwest - ID, OR, WA
How often is the US Northwest climate update refreshed?
The US Northwest climate update is refreshed monthly, typically a few days after the previous month closes and the upstream provider (Met Office HadUK-Grid, NOAA Climate at a Glance, Copernicus ERA5 or the Global Carbon Project) publishes its update. See the Climate Rankings for cross-region comparisons.
What counts as a Heatwave Day on the US Northwest climate page?
Heatwave Days use the Warm Spell Duration Index (WSDI) - the WMO/ETCCDI-standard heatwave measure: days that are part of a run of 6 or more consecutive days above the local 90th-percentile temperature for that calendar day. The 90th-percentile threshold varies by time of year (a hot day in January is judged differently to one in July) but is fixed to the 1961-1990 baseline for every year shown - it does not shift as the climate warms, which is why Heatwave Days trend upward over time.
Does the US Northwest climate page include frost and snow data?
Yes. Frost Days (days with a minimum temperature below 0°C, World Bank CCKP) and snow water-equivalent (GPCC) are shown alongside temperature and precipitation, each measured against the 1961-1990 baseline where a like-for-like historical comparison is available.
What major climate events has the US Northwest experienced?
Major climate events in the US Northwest include The 1910 'Big Burn'; The 1976-77 drought; The 2002 Western drought; Post-2013 acceleration in US temperatures; The 2015 western snow drought. The Climate History panel on this page lists 38 sourced events and pattern shifts relevant to the US Northwest, the earliest from 1910 - 10 about the US Northwest itself and the rest global context such as volcanic eruptions and El Niño events. Each entry carries its own sources and can be searched, filtered to local events or by category, and sorted by date; scrolling the list moves a cursor across the chart above so you can see where each event falls in the record.
Where does the Climate History list for the US Northwest come from, and how is it checked?
It is a hand-reviewed register, not an automatic feed. Every entry is sourced, and each one records how it was verified - against this site's own data series, against a peer-reviewed paper, or against the public record of the event. 19 of the 38 entries here are written specifically about the US Northwest, usually quoting its own ranking or measured figures. The rest give global or national context shared with wider pages. Where a figure is narrower than it first appears, or a famous claim does not hold locally, the entry says so.
We use cookies for ads, social features and analytics, and share how you use the site with our advertising, social media and analytics partners. Privacy Policy
