North Atlantic Oscillation - NAO Tracker
The North Atlantic Oscillation is 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 rams Atlantic storms into northern Europe; in its negative (-NAO) phase the jet buckles south and lets Arctic air flood in. This page combines the live NOAA daily index, the 75-year monthly history and the Atlantic Multidecadal Variability (AMV) ocean background that tilts the NAO across whole decades.
Current State - Negative (-NAO) · on Warm (+AMV) Background
The North Atlantic Oscillation is the pressure see-saw between the Icelandic Low and Azores High. Its famous mild/cold winter grip is out of season: in high summer the weaker summer NAO tilts the UK between warm-dry-sunny (positive) and cool-wet-cloudy (negative) patterns.
NAO phase - latest
Negative (-NAO)
-1.28 · 2026-07-31
30-day rolling mean
-0.31 · 2026-07
N.North 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.
NAO phase - latest
Negative (-NAO)
-1.28 · 2026-07-31
30-day rolling mean
-0.31 · 2026-07
Atlantic Multidecadal Variability (background)
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 positive to negative on 2026-07-26 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.
History (1950-present)
NAO History
Daily NAO swings inside individual winters; monthly NAO shows the longer regime shifts. Green bands mark sustained +NAO (mild/wet Europe); violet bands mark sustained -NAO (cold/blocked Europe). Sky-blue vertical strips are Dec-Feb, the season that matters most for UK & European weather.
NOAA classifies the NAO from a rotated-principal-component analysis of 500 hPa geopotential heights across the Northern Hemisphere. The thin grey line is raw monthly values; the gold trendline is the 12-month rolling mean - visible regime shifts include the famously +NAO 1990s and the -NAO blocking cluster around 2009-2013. The monthly index is the more useful indicator for seasonal forecasting. Data: NOAA CPC daily NAO · monthly NAO.
AMV Ocean Background
AMV Background - Warm (+AMV) since ~2000
Atlantic Multidecadal Variability is the 20-40 year warm/cool baseline of North Atlantic sea-surface temperatures. It tilts the NAO and Atlantic hurricane activity across whole decades, not single seasons.
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
Rose / sky bands show the conventional Atlantic warm / cool periods used in the literature (Enfield et al. 2001; Trenberth & Shea 2006). Grey line: unsmoothed annual North-Atlantic SST anomaly. Gold line: low-pass smoothed series used to classify the multidecadal background. Data note: NOAA PSL’s Kaplan-SST AMO file currently only publishes through Jan 2023 (annual through 2022); the smoothed series lags a further ~5 years because of the low-pass filter and PSL’s update cadence. The page shows the latest values NOAA distributes. Data: NOAA PSL AMO long monthly series.
Regional Impacts
Where Does the NAO Bite Hardest?
The NAO's footprint is concentrated on the North Atlantic rim. Below is the canonical winter (Nov-Mar) pattern for each phase, with today's live regime highlighted at the top. High summer (Jul-Aug) plays by different rules - the summer NAO - and the UK rainfall sign flips.
Live: -NAO regime today · summer NAO pattern
- UK, Ireland, Scandinavia -Cooler · wetter · cloudier
- Mediterranean, S. Europe -Tilted hotter · drier
Summer NAO relationships are weaker than winter ones, and the UK rainfall sign flips: positive summers lean dry and sunny where positive winters lean wet and stormy.
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. Germany
Mild · wet · windy winters - Strong westerly jet drives Atlantic storms across the British Isles into mainland Europe. Flooding risk elevated. - Mediterranean, Iberia, N. Africa
Drier · cooler - Storm track pushed north; subtropical high dominates. Worsens drought stress in already dry years. - Eastern US, SE Canada
Milder winters - Fewer cold-air outbreaks; coastal storms tend to track further offshore. - Greenland, NE Canada, Labrador
Colder · snowier - Reinforced trough over Baffin Bay channels Arctic air south.
Negative NAO (-NAO) · winter
- UK, Ireland, Scandinavia, N. Germany
Colder · stiller · snowier - Buckled jet allows Arctic air to plunge south. High-latitude blocking patterns dominate. - Mediterranean, Iberia, N. Africa
Wetter · stormier - Storm track diverted south; episodic flooding around Atlas, Pyrenees and SE Spain. - Eastern US, SE Canada
Cold outbreaks · Nor’easters - Polar air discharges south more often. Snowstorms hit the eastern seaboard harder. - Greenland, NE Canada
Relatively mild - Reduced 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.
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 speed up or slow down at any moment, while AMOC weakening is a long-term, near-irreversible shift driven by Greenland melt and warming surface waters.
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.
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.