ENSO events vary in strength, thus impacts from each ENSO event can differ and predicting these effects can be difficult. Climatologies of El Niño events have been developed over the past several decades and have found that in general, warmer and slightly drier wintertime conditions occur in the Midwest during El Niño. For La Niña events, cooler and wetter wintertime conditions occur. These impacts can be seen in the images below.

El Niño winter pattern. Source: climate.gov

La Niña winter pattern. Source: climate.gov

During the heart of the summer (June, July, and August), ENSO events have a lesser impact on Midwest temperature and precipitation patterns. ENSO events are usually weaker during the summer months. In addition, ENSO mainly influences the location of the jet stream over North America. The jet stream is weaker and farther north during the summer months, minimizing the effects of ENSO on weather in the United States.

ENSO diagnostic and attribution tools can be retrieved from the Climate Prediction Center's website, where information regarding seasonal US temperature, precipitation, and snowfall impacts based on historical ENSO episodes. An example of the maps available can be seen below.

CPC Diagnostic Tools