ONI · NOAA Climate Prediction Center CC0 · public domain

The Zero Horizon

Seventy-six years of the Oceanic Niño Index — the observed sea-surface anomaly that names each season El Niño (warm), La Niña (cool), or neutral. The horizon line is zero: warm fills up, cool fills down. One climate gauge, read straight from the record — never a forecast.

Latest observed seasonAMJ 2026
ONI anomaly+0.98°C
Regime as observedEl Niño territory

The record ends mid-2026 climbing out of the 2025 La Niña trough (SON 2025 −0.51°C). This is the tracked record ending on a warm upswing, described as observed. No value here is extrapolated forward.

The signature view

The zero-horizon ribbon

Every one of the 917 overlapping three-month seasons since DJF 1950, as a diverging area around a hard zero line. Rust fills upward for El Niño, teal fills downward for La Niña, and the guide lines mark the ±0.5°C thresholds. The pale ribbon is the full record; the saturated runs are the 42 official episodes. Nearly half the record — 45.6% — sits in the quiet neutral band, so ENSO reads as episodic punctuation, not a constant seesaw.

Sonification maps anomaly to pitch (warm = higher, cool = lower) as a play-through; a moving caret and the readout track it, and every value is also in the episode and seasonal tables below. Audio is an enhancement, never the only channel.

Diverging area chart of the Oceanic Niño Index, DJF 1950 through AMJ 2026. The observed ONI anomaly around a zero horizon: warm El Niño lobes fill upward, cool La Niña lobes fill downward, threshold guides at plus and minus 0.5 degrees C. Reads the regime by which side is filled and how far. Observed record, not a forecast.
Scroll the strip or drag the slider to read any season. El Niño owns the sharpest peaks (record +2.75°C, NDJ 2015); La Niña's floor is −2.03°C (NDJ 1973).

Walk the data

Scattered peaks, one heartbeat

El Niño and La Niña can begin in any season. Watch where the big ones peak. Below are three of the strongest warm events; a tick marks the season each one topped out. Every tick lands in late autumn or winter.

Peak season of three major El Niño events. 1982-83 peaks at NDJ, 1997-98 peaks at OND, 2015-16 peaks at NDJ — all in the November-to-January winter window.
Across all 42 official episodes, 34 of 42 reach peak intensity in the Oct–Mar window and 32 of 42 peak specifically in OND / NDJ / DJF. ENSO doesn't peak randomly — it locks to boreal winter.

Now fold those scattered peaks onto a single dial. The clock below places all 76 years of every season around a ring — and the same winter seasons that caught the peaks are exactly where the ring bulges widest.

The non-obvious form

The phase clock

One spoke per overlapping season, DJF around to NDJ. Each spoke's length is the spread (standard deviation) of all 76 years of anomalies in that season. The dial bulges through NDJ / DJF / OND (std 1.03–1.09) and pinches to its narrowest waist at AMJ / MJJ (std ≈ 0.56 — a tight spread, not zero; the radius is short, the anomalies still vary). This is the seasonal phase-lock made into one glanceable shape — ENSO's heartbeat, wide in winter, narrow in spring.

Radial dial of ONI spread by season. Twelve spokes, one per overlapping season. Spoke length encodes the standard deviation of the anomaly across all years. The dial is widest at NDJ, OND and DJF (winter) and narrowest at MAM, AMJ and MJJ (spring), showing the seasonal phase-lock.

Winter seasons carry roughly twice the spread of spring seasons. Select a season to read its spread.

Seasonal spread — full table
Standard deviation and median of the ONI anomaly by overlapping season, all years 1950–2026. Source: NOAA CPC ONI (CC0).
SeasonStd dev °CMedianMinMax
DJF1.03−0.19−1.84+2.63
JFM0.87−0.02−1.55+2.28
FMA0.70+0.06−1.29+1.71
MAM0.59+0.15−1.18+1.29
AMJ0.56+0.02−1.07+1.06
MJJ0.58+0.00−1.30+1.25
JJA0.65+0.07−1.30+1.60
JAS0.74−0.07−1.35+1.91
ASO0.86−0.12−1.56+2.21
SON0.97−0.17−1.71+2.47
OND1.07−0.15−1.95+2.64
NDJ1.09−0.12−2.03+2.75

The asymmetry & the browser

Twin span-bars: the sprinter and the marathoner

El Niño episodes stack above the zero line, La Niña below; bar length is duration in seasons. La Niña bars run longer and, above all, repeat — five distinct multi-year events, the 1998–2001 and 2021–2023 dips re-intensifying across three to four consecutive winters, a double-dip pattern El Niño doesn't make in this record. El Niño's longest runs (2014–16, 1986–88) can span three calendar years too, but each holds a single peak and fades rather than re-deepening winter after winter. And El Niño owns the sharper ceiling. Warm events spike higher; cool events last longer and repeat. Select any bar or table row to walk through that episode.

Timeline of all 42 official ENSO episodes, El Niño above zero and La Niña below. Horizontal bars positioned by calendar time; bar length is episode duration in seasons. El Niño episodes sit above the center line, La Niña below. La Niña bars run longer and repeat, clustering into multi-year double-dip runs; El Niño episodes hold a single peak and, though a few span three calendar years, do not re-deepen across successive winters.
Longest La Niña: 32 seasons (1998–2001). Longest El Niño: 19 seasons (2014–16). El Niño's sharper ceiling (+2.75) versus La Niña's floor (−2.03).
All 42 official ENSO episodes — five or more consecutive overlapping seasons past the ±0.5°C threshold. Select a row to open its rise–peak–decay walk-through. Column headers sort. Source: NOAA CPC ONI (CC0, public domain).
La Niña 1950-50DJF 1950–JJA 19507DJF 1950−1.53
El Niño 1951-52MJJ 1951–DJF 19528SON 1951+1.15
El Niño 1953-54JFM 1953–DJF 195412SON 1953+0.84
La Niña 1954-56AMJ 1954–JAS 195628OND 1955−1.67
El Niño 1957-58MAM 1957–JJA 195816DJF 1958+1.81
El Niño 1958-59OND 1958–FMA 19595JFM 1959+0.62
El Niño 1963-64MJJ 1963–JFM 19649OND 1963+1.37
La Niña 1964-65AMJ 1964–DJF 19659OND 1964−0.82
El Niño 1965-66MJJ 1965–MAM 196611SON 1965+1.98
El Niño 1968-69SON 1968–AMJ 19698DJF 1969+1.13
El Niño 1969-70JAS 1969–DJF 19706SON 1969+0.86
La Niña 1970-72JJA 1970–DJF 197219JFM 1971−1.38
El Niño 1972-73AMJ 1972–FMA 197311NDJ 1972+2.12
La Niña 1973-74AMJ 1973–JJA 197415NDJ 1973−2.03
La Niña 1974-76SON 1974–FMA 197618NDJ 1975−1.65
El Niño 1976-77ASO 1976–JFM 19776OND 1976+0.86
El Niño 1977-78ASO 1977–DJF 19785OND 1977+0.81
El Niño 1982-83AMJ 1982–MJJ 198314NDJ 1982+2.23
La Niña 1984-85SON 1984–MJJ 19859NDJ 1984−1.14
El Niño 1986-88ASO 1986–JFM 198818JAS 1987+1.70
La Niña 1988-89AMJ 1988–AMJ 198913NDJ 1988−1.85
El Niño 1991-92MJJ 1991–MJJ 199213DJF 1992+1.71
El Niño 1994-95ASO 1994–FMA 19957NDJ 1994+1.09
La Niña 1995-96JAS 1995–FMA 19968OND 1995−1.00
El Niño 1997-98AMJ 1997–MAM 199812OND 1997+2.40
La Niña 1998-01JJA 1998–JFM 200132DJF 2000−1.66
El Niño 2002-03MJJ 2002–JFM 20039OND 2002+1.31
El Niño 2004-05JAS 2004–JFM 20057ASO 2004+0.70
La Niña 2005-06OND 2005–FMA 20065DJF 2006−0.85
El Niño 2006-07ASO 2006–DJF 20075OND 2006+0.94
La Niña 2007-08JJA 2007–MJJ 200812DJF 2008−1.64
La Niña 2008-09OND 2008–FMA 20095DJF 2009−0.85
El Niño 2009-10JAS 2009–FMA 20108NDJ 2009+1.56
La Niña 2010-11MJJ 2010–MAM 201111SON 2010−1.64
La Niña 2011-12JAS 2011–JFM 20127OND 2011−1.02
El Niño 2014-16SON 2014–MAM 201619NDJ 2015+2.75
La Niña 2017-18SON 2017–FMA 20186NDJ 2017−0.86
El Niño 2018-19ASO 2018–MJJ 201910OND 2018+0.97
El Niño 2019-20OND 2019–FMA 20205NDJ 2019+0.66
La Niña 2020-21JAS 2020–MAM 20219OND 2020−1.20
La Niña 2021-23ASO 2021–DJF 202317ASO 2022−0.97
El Niño 2023-24AMJ 2023–MAM 202412NDJ 2023+2.06

What the record earns

Five honest reads

Phase-lock is real and stark

32 of 42 official episodes peak in OND/NDJ/DJF, 34 of 42 in Oct–Mar. Seasonal spread climbs from ~0.56 in spring to ~1.09 in NDJ. The dataset has a spring waist and a winter bulge.

Sprinter vs marathoner

La Niña reaches 28 and 32 seasons and stages 5 multi-year events; El Niño's longest single run is 19 and, though it can span three calendar years, it doesn't double-dip across winters. But El Niño owns the extremes: +2.75 ceiling vs −2.03 floor.

Detrended by design

Raw SST drifts up across decades, but the anomaly stays centered on zero — ONI is measured against a moving 30-year base. A regime index that removes the warming trend, not a climate-warming line. Flip the detrend toggle above to see it.

A balanced seesaw

Over 76 years the record splits 26.9% El Niño / 27.5% La Niña / 45.6% neutral — remarkably symmetric time-in-state, even though the intensity distribution is not.

The live tail (observed)

The record ends climbing out of a La Niña trough — SON 2025 −0.51 up through MAM 2026 +0.51 to AMJ 2026 +0.98. An emerging warm signal in the observed record, described as observed — never extrapolated.