What kind of ENSO path is this?
El Niño and La Niña are not single events but links in a chain. A super El Niño after years of La Niña can snap straight back into La Niña, fade to neutral, or linger. This library sorts every ENSO path since 1940 by plain, stated rules, shows what each year of each kind of sequence did to U.S. winters, and asks which kind of path 2025–28 is on.
Where we are on the path
Every winter since 1940, and the paths the rules find
Dec–Feb ENSO index, every winter, with each archetype's sequences beneath
The library
rules, members, and whether other indices agreeWhat each year of the sequence did to U.S. winters
Duration is the damage
precipitation departures that add up across yearsA single dry winter is a setback; two or three in a row empty soils, reservoirs and aquifers. This map adds up each division's water-year (October–September) precipitation departure across the years of every past sequence of the kind chosen, then averages across sequences.
Would the data find the same groups on its own?
How to read this, and what it cannot tell you
The rules decide, not a model. Each winter gets a phase from its Dec–Feb index: El Niño at +0.5σ or more, La Niña at −0.5σ or less, neutral in between. A path is three winters in a row (years 1, 2 and 3), and the archetype is read off their phases. The winter before year 1 is checked only to make sure a double or triple dip starts at its first La Niña winter and a long neutral at its first quiet one.
Small samples. The whole record since 1940 holds only a handful of each kind of path. With three members, no division can pass the significance test even if all three winters landed in the same third, so the single-archetype maps are a list of three winters drawn on a map, not a forecast. The pooled families (El Niño → La Niña, multi-year La Niña) have five to nine members. Read the counts, not the colours.
The index matters. Borderline winters change sides between indices, and with them whole sequences change archetype: 1971–72 is La Niña on NOAA's ONI but neutral on the primary index, which turns the 1972–74 path from a whiplash into "warm to cold". Each card says how many of its members another index agrees on.
Related routes: the 2027–28 transition watch, trajectory analogs, draw your own path, drought and pluvial debt.