Temperature Departures in Illinois During the 1982-83 and 1997-98 El Nino

The bar graph below summarizes the monthly temperature pattern for the past two strong El Niño events in Illinois – the 1982-83 event and 1997-98 event. The warmer than average winters stand out while the results for fall and spring are mixed.

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In the fall as El Niño starts to develop, both of the earlier events tended to be a little cool at times, but not in a consistent way. Overall, the 1997-98 event was cooler thanks to the exceptionally cold November.

By December warmer than average temperatures were associated with El Niño, a classic pattern for stronger events. However, if you look closely, the nature of the warming differed between the two. The 1982-83 event had its warmest departures in December and less so in January and February. On the other hand, the 1997-98 event clearly ramped up with relatively cold temperatures in November, and each following month showing stronger above-average temperature departures through February.

By spring, the story gets complicated. By March, the influence had disappeared. April was colder than average for the 1982-83 event while near-average for the 1997-98 event. For May, Illinois temperatures were colder than average for the 1982-83 event and warmer than average for the 1997-98 event. That is hardly a consistent pattern.