4 Billion Years On

North Atlantic Oscillation

The pressure see-saw behind UK and European winters - mild and stormy, or cold and still…

The pressure see-saw between the Icelandic Low and the Azores High - the single most important driver of UK and European winter weather. In its positive (+NAO) phase a strong westerly jet drives Atlantic storms into northern Europe; in its negative (-NAO) phase the jet buckles south and lets Arctic air in. With the live NOAA daily index, 75 years of monthly history and the Atlantic Multidecadal Variability (AMV) ocean background.

Latest data 14 Oct 2026

Current State

Icelandic Low vs Azores High: strongest in winter (Nov-Mar) - between seasons, context rather than a forecast.

NAO phase - latest

Positive

+0.77 · 2026-10-14

30-day rolling mean

+0.37σ

+0.53 · 2026-09

N. Atlantic

Azores High and Icelandic Low are the two NAO action centres - their pressure difference defines the index. The shaded box is the AMV domain (0-60°N, 80°W-0°); rose = warm phase, sky = cool phase.

Atlantic Multidecadal Variability

Warm
+0.17°C smoothed· since ~2000

AMV (also called the Atlantic Multidecadal Oscillation, AMO) is the slow 20-40 year warm/cool baseline of the North Atlantic. Warm-AMV decades tilt the NAO positive on average and supercharge Atlantic storms; cool-AMV decades favour more blocking and -NAO episodes.

Sustained sign flip detected

NAO crossed from negative to positive on 2026-10-02 and has held the new sign for at least five days. This often marks a genuine jet-stream regime change rather than weather noise.

Thresholds: ≥ +0.5σ Positive · ≤ -0.5σ Negative · otherwise Neutral. Data: NOAA CPC daily NAO - monthly NAO - NOAA PSL AMO/AMV.

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History

Daily & Monthly NAO

Daily swings within winters, and the monthly regime shifts since 1950.

Daily NAO · last 730 days
+NAO (mild, wet Europe)-NAO (cold, blocked)30-day meanDaily valuesDec-Feb winters
Monthly NAO · 1950-present
+NAO (mild, wet Europe)-NAO (cold, blocked)12-month meanMonthly values

Note the +NAO 1990s and the -NAO blocking of 2009-13. NOAA derives the index from 500 hPa heights (rotated principal components). Data: NOAA CPC daily NAO · monthly NAO.

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Ocean Background

Atlantic Multidecadal Variability (AMV)

The 20-40 year warm/cool swing in North Atlantic sea temperatures that tilts the NAO and hurricane activity over decades - often linked to the AMOC.

Smoothed (latest)

+0.17°C

2017 · low-pass filtered

Unsmoothed (latest)

+0.19°C

Jan 2023

Phase start

2000

last sign change in smoothed series

Warm-AMV decade Cool-AMV decade Annual Smoothed (low-pass)

Bands: the accepted warm and cool periods (Enfield et al. 2001; Trenberth & Shea 2006). Grey: annual North Atlantic SST anomaly; violet: the smoothed series that sets the phase. NOAA PSL’s Kaplan-SST file runs to Jan 2023 (annual to 2022), and smoothing lags it ~5 years more. Data: NOAA PSL AMO long monthly series.

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Regional Impacts

Where Does the NAO Bite Hardest?

Each region's usual winter (Nov-Mar) response to each NAO phase, with today's phase shown first - in high summer the UK rainfall signal flips.

Live: +NAO today · transition season

The index is positive, but NAO weather impacts are strongest in winter (Nov-Mar), with a weaker, different-signed high-summer pattern (Jul-Aug). In the transition seasons the link between the index and UK/European weather is loose - treat today's phase as context rather than a forecast.

AMV background modulator

Warm-AMV background amplifies +NAO storminess and weakens -NAO cold spells across northern Europe.

Positive NAO (+NAO) · winter

  • UK, Ireland, Scandinavia, N. GermanyMild · wet · windy wintersStrong westerly jet drives Atlantic storms across the British Isles into mainland Europe. Flooding risk elevated.
  • Mediterranean, Iberia, N. AfricaDrier · coolerStorm track pushed north; subtropical high dominates. Worsens drought stress in already dry years.
  • Eastern US, SE CanadaMilder wintersFewer cold-air outbreaks; coastal storms tend to track further offshore.
  • Greenland, NE Canada, LabradorColder · snowierReinforced trough over Baffin Bay channels Arctic air south.

Negative NAO (-NAO) · winter

  • UK, Ireland, Scandinavia, N. GermanyColder · stiller · snowierBuckled jet allows Arctic air to plunge south. High-latitude blocking patterns dominate.
  • Mediterranean, Iberia, N. AfricaWetter · stormierStorm track diverted south; episodic flooding around Atlas, Pyrenees and SE Spain.
  • Eastern US, SE CanadaCold outbreaks · Nor’eastersPolar air discharges south more often. Snowstorms hit the eastern seaboard harder.
  • Greenland, NE CanadaRelatively mildReduced trough lets Atlantic air reach high latitudes. Greenland melt season starts earlier.

Composite from Hurrell (1995, Science), Scaife et al. (2014, GRL) and Met Office GloSea seasonal-forecast verification; summer NAO relationships from Folland et al. (2009, J. Climate). Stratospheric sudden warmings often precede sustained -NAO episodes by 2-4 weeks - see the Stratospheric Polar Vortex tracker for the upstream signal.

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FAQs

North Atlantic Oscillation: Common Questions

What is the North Atlantic Oscillation (NAO)?

The North Atlantic Oscillation is a large-scale atmospheric pressure see-saw between the subpolar low near Iceland and the subtropical high near the Azores. It is the single most important driver of winter weather across western Europe, the eastern United States and the Mediterranean, because it dictates the strength and path of the Atlantic jet stream.

What does a positive NAO (+NAO) mean for the UK and Europe?

A positive NAO (+NAO) means both the Icelandic Low and the Azores High are stronger than average, driving a powerful westerly jet stream straight across the Atlantic. Northern Europe - including the UK, Ireland, Scandinavia and northern Germany - tends to get mild, wet and windy winters with successive storm systems. The Mediterranean, by contrast, stays drier and cooler than average.

What does a negative NAO (-NAO) mean for the UK and Europe?

A negative NAO (-NAO) weakens the Icelandic Low and Azores High. The Atlantic jet stream buckles and shifts south, allowing frigid Arctic air to plunge into northern Europe. The UK and northern Europe typically see colder, snowier and stiller winters with high-latitude blocking patterns. Southern Europe and the Mediterranean instead get heavier rain and storm tracks.

How does the NAO affect the eastern United States?

A positive NAO is associated with warmer-than-average winters in the eastern US with fewer cold-air outbreaks. Eastern Canada and Greenland, however, tend to be colder and snowier. A negative NAO does the opposite: more frequent cold-air outbreaks and Nor’easter storms hitting the eastern seaboard, while Greenland stays relatively mild.

Which countries does the NAO affect most?

Measured on this site from each place's seasonal temperature and rainfall since 1950 (with the long-term trend and El Niño / La Niña's share removed), the NAO's strongest fingerprints are in winter: around half of the year-to-year swing in December-February rainfall in Scotland (wetter with a positive NAO), Greenland's winter temperature (colder with a positive NAO), and winter rainfall in Spain and Morocco (drier with a positive NAO), plus milder winters across Denmark, Sweden and the Baltic states. The summer NAO matters too - a positive summer NAO goes with drier summers in England and Wales. Every country and region page shows whether the NAO measurably matters there, in its Climate Drivers section.

Is the NAO the same thing as the Atlantic Meridional Overturning Circulation (AMOC)?

No. The NAO is an atmospheric pressure pattern that changes day-to-day and month-to-month. The AMOC is an ocean current that turns over slowly across decades. They are linked but distinct - the NAO can flip within weeks, while the AMOC changes over decades. Whether the AMOC is already weakening is still debated; the AMOC page on this site shows the direct measurements and the evidence.

How is the NAO measured?

The NAO is calculated as the standardised difference in sea-level pressure between a station representing the subtropical high (the Azores, Lisbon or Gibraltar) and one representing the subpolar low (Iceland). NOAA uses a rotated-principal-component method to extract the daily and monthly index values shown on this page, anchored to the 1950-present record.

How often does the NAO flip phase?

On the order of weeks to months. Unlike ENSO (which evolves over years) the NAO can swing from strongly positive to strongly negative inside a single winter. Sustained sign flips lasting five or more days are detected and flagged in the current-state tracker because they often signal a real change in the jet-stream regime.

What is the Atlantic Multidecadal Variability (AMV / AMO)?

The Atlantic Multidecadal Variability (also called the Atlantic Multidecadal Oscillation) is the slow, 20-to-40-year see-saw in North Atlantic sea-surface temperatures. It acts as the background baseline against which the NAO operates: warm-AMV decades bias the NAO toward more frequent positive phases and supercharge Atlantic winter storms, while cool-AMV decades favour more blocking and -NAO episodes.

How does climate change affect the NAO?

Recent peer-reviewed work (Met Office, University of Exeter, 2024-25) finds that NAO swings under high-emission scenarios are reaching magnitudes not seen in the historical record. This is interpreted as climate change amplifying the extremes of both NAO phases, meaning more severe flooding and storm damage during +NAO winters and more disruptive deep-cold outbreaks during -NAO winters across northern Europe.

Is there a seasonal forecast for the NAO?

Forecasters (Met Office, ECMWF and others) do publish qualitative seasonal commentary on the Atlantic jet stream and storm track from time to time, and these are worth reading directly for the current season's expectation. The NAO chart on the Climate Symphony deliberately doesn't turn that kind of commentary into a projected line, though - a hand-transcribed take from a blog post or report goes stale fast, and a generic statistical carry-forward can just as easily contradict what a real forecast center is actually saying. Rather than show a line that might be wrong in either direction, the NAO chart shows observed history only, with no forecast dashing, until a live automated seasonal-forecast feed exists for the NAO to plot from directly.

Where does the data on this page come from?

The daily and monthly NAO index come from the NOAA Climate Prediction Center (CWLinks dataset, 1950-present), built using a rotated-principal-component analysis of 500-hPa geopotential heights. The AMV/AMO series come from the NOAA Physical Sciences Lab (Kaplan SST V2). Snapshots are rebuilt nightly via GitHub Actions, so the page always reflects the latest published values.

How often is the tracker updated?

Daily. The NOAA CPC daily NAO index publishes a new value every day; our snapshot rebuilder runs nightly and the page reflects the new value the next time it is requested.