This map shows the historical probability (given in percentile) of seasonal average monthly minimum or maximum temperature falling within the upper (hot), middle (normal), or bottom (cold) one-third ("tercile") of the 1961 to 2020 historical distribution in the country given the state of ENSO (El Niño, Neutral, La Niña) during the previous season (e.g. Jan-Mar temperature against Oct-Dec ENSO state).
Here, the ENSO state for each season is defined according to the Oceanic Niño Index (ONI). It is calculated using Sea Surface Temperature (SST) anomalies, based on centered 30-year base periods updated every 5 years, in the geographical box (170˚W, 5˚S, 120˚W, 5˚N). A season is considered El Niño (La Niña) if it is part of at least 5 consecutive overlapping 3-month long seasons where the ONI is above 0.5˚C (below -0.5˚C). Use the controls on the page to select the season, rainfall tercile category of interest, and ENSO state. The analysis reproduces, using same SST dataset, the following definition from NOAA.
Clicking on the map will then display, for the selected point, yearly seasonal minimum or maximum temperature averages time series. The colors of the bars depict what ENSO phase it was that year, and the horizontal lines show the historical terciles limits. This allows to quickly picture what years fell into what ENSO Phase and into what Temperature Tercile category.
While the rainfall response to ENSO is nearly contemporaneous, this is not true for temperature. Once El Niño (La Niña) has begun, there is a ramp up (down) of global temperatures which are then slow to dissipate after the return to a neutral phase. Because of this we lag the temperature response to ENSO phases by 3 months.
NB: This is not a forecast. It is based just on historical observations of minimum or maximum temperature and SST. However, it would be a good tool for exploring the effect of different ENSO phases on the following seasonal temperature.
Reference for ENSO phases definition: V. E. Kousky and R. W. Higgins, 2007: An Alert Classification System for Monitoring and Assessing the ENSO Cycle. Wea. Forecasting, 22, 353-371. doi: http://dx.doi.org/10.1175/WAF987.1
Contact help@iri.columbia.edu with any technical questions or problems with this Map Room.