ENSO is a cycle with memory. Plan for the sequence, not the event.
A single El Niño or La Niña forecast answers “what about this winter?” The decisions that carry the most money and the most risk run longer: stocks carried from one harvest to the next, reinsurance bought a year ahead, reservoirs managed across water years, budgets and aid set for several. Over those horizons what matters is the regime: a La Niña in its second or third year, an El Niño that follows one, the whiplash between them, and the slow oscillations underneath that tilt every event for years.
Every number on this page is a link to its data file (hover the dotted numbers). Years are ENSO winters labelled by the January of the peak (1997–98 = 1998). Counts are “k of n” events; with ten or fewer events, even 9 of 10 carries a wide interval, and only results marked passes FDR survive the correction for the number of tests.
Seventy-eight winters, and what came with them
1949–50 to 2026–27The regime timeline, with sector outcomes aligned underneath
Top: each winter's ENSO state and strength, the multi-year La Niña runs bracketed, and the PDO, the Indian Ocean Dipole and the QBO below it. Underneath, on the same years: synchronous maize failures, three breadbasket yields that the regimes move most, U.S. crop-insurance and billion-dollar losses, Atlantic hurricane energy, stratospheric warmings and global record years. Hover any year; highlight a regime to see where its outcomes fall.
ENSO has memory: La Niña lingers, and El Niño sets up what comes next
El Niño and La Niña are not mirror images. Most El Niños end within a year; La Niñas often last two or three. Since 1949–50, – La Niña episodes (counted by winter) lasted two winters or more (–), against – El Niño episodes. A strong El Niño discharges the heat stored in the equatorial Pacific, and the ocean often swings past neutral: La Niña followed – strong El Niños the next winter (–). The literature explains why, and why the sequence is partly predictable a year or two ahead.
Regimes move sectors that single events do not
Split the record by where a year sits in the sequence and some of the clearest results in the site's data appear. Crops: breadbaskets fail together in the second and third years of La Niña (the figure above); Argentina's maize was below the neutral median after – second-or-later La Niña winters (mean – of trend); South Africa's after – strong El Niños (–); Australia's wheat in – years while an El Niño developed (–). Prices: real palm-oil prices were higher 24 months after – El Niño onsets. Insurance: crop-insurance drought losses ran above trend in – La Niña crop years (not significant after correction); Atlantic hurricanes were fewer than the neutral trend in – seasons while a strong El Niño developed. Winter: strong El Niños that followed a multi-year La Niña were barely warm across the Lower 48 (– against – for the other six), and every El Niño after a multi-year La Niña since 1959 had a major stratospheric warming (–, against – of all winters). Heat: U.S. summer cooling demand was above normal after – El Niño peaks.
The null results matter as much. Billion-dollar disaster counts and costs, the total crop-insurance loss cost, heating demand, gas storage and winter gas prices, and southern tornado springs show no regime signal at all (–, –, – and – tests pass). A regime tells you which perils and which places, not the size of a year's national bill.
The evidence ledger
Every headline result and every null, side by side. Click through for the full comparisons.
The slower oscillations tilt every event for years
The Pacific Decadal Oscillation has been negative in – months since January 2020 (NCEI ERSSTv5, mean –). When the PDO is negative, El Niño's North American pattern is weaker and less reliable; when it is positive the two add up (Gershunov and Barnett 1998; Maher et al. 2022). A cool Pacific with a warm Atlantic has been the background of the worst U.S. multi-year droughts. The Indian Ocean Dipole decides much of what El Niño does to Australia, East Africa and India, and the QBO shifts the odds of a stratospheric warming. None of these is an ENSO forecast, but each changes what a given ENSO event delivers, and each persists for months to decades.
The decisions already run on multi-year horizons
The people who carry ENSO risk rarely decide one season at a time. What each of them can take from the regime record:
By sector, and for this winter
Related: compounding pathways · the compound ledger · the year after · the archetype library · the 2027–28 transition · the stratosphere · sectors · intelligence briefs · the planet.
How the numbers were made
Regimes. Each ENSO winter is classed by CPC's Oceanic Niño Index (the most extreme of OND, NDJ and DJF; ±0.5 °C), its strength by the peak 3-month value (strong at 1.5 °C or more), and its place in the sequence: a first, second or third La Niña year; an El Niño that follows two or more La Niña winters (1957–58, 1972–73, 2009–10 and 2023–24 among the strong ones). The PDO is the NCEI ERSSTv5 index averaged over the 12 months before the winter. On the relative index (RONI) some years change class, 2024–25 among them; the pages say so where it matters.
Tests. Every outcome has its trend removed first, fitted on neutral years only. A regime's years are counted above or below the neutral years' median, with 95% Wilson intervals; Mann–Whitney and sign tests compare them with the neutral years; and the Benjamini–Hochberg false-discovery rule (q = 0.10) is applied across every family of tests, so a count that looks striking among hundreds of comparisons is not over-read. Groups overlap (2023–24 is strong, very strong, after a multi-year La Niña and negative-PDO), so they are not independent.
Literature. Every paper cited was checked against Crossref (title, first author, year); web sources carry their URL check, and findings not checked against an abstract are flagged on their cards. The data, the tests and the caveats are documented in the data files' schema; nothing here is a forecast except where the 2026–27 page says so.