The National Oceanic and Atmospheric Administration (NOAA) forecasts that Chicago and much of Illinois will experience above-average temperatures in the coming months due to the ongoing El Niño weather phenomenon. Illinois state climatologist Trent Ford said the region faces about a 70% chance of warmer-than-normal temperatures from December through February, a prediction he described as highly reliable in terms of temperature but less so for precipitation trends.
El Niño, part of the El Niño-Southern Oscillation cycle characterized by warming in the Pacific Ocean, is currently one of the strongest on record, amplified by human-driven climate change. Zack Leasor, state climatologist at the University of Missouri, noted this could result in one of the most significant weather events in recent history. While much of the United States is expected to see normal or above-average temperatures, precipitation patterns remain uncertain, with Illinois and the surrounding regions facing equal odds for wetter or drier conditions.
The warmer temperatures are already impacting the region’s fall foliage. Michael Jesiolowski, plant clinic manager at The Morton Arboretum, explained that leaf color changes are often triggered by colder temperatures, particularly nights near or below freezing. However, as of mid-October, temperatures have remained relatively mild, delaying the display of vibrant fall colors. Jesiolowski anticipates later but potentially longer-lasting foliage hues this season, depending on factors like sunlight and rainfall.
Agricultural impacts from El Niño are expected to be mixed. According to botanist David Zaya of the Illinois Natural History Survey, El Niño years tend to produce higher yields in corn and soybeans due to a longer growing season and fewer obstacles during planting. Conversely, warmer conditions may promote the survival of more pests and early-emerging weeds, such as marestail, which could require increased herbicide use. Zaya expressed concern over the potential spread of these chemicals into nearby natural areas, many of which already show damage from herbicide drift. Additionally, the warm winter could accelerate the spread of invasive plants like the Japanese chaff flower in southern Illinois.
El Niño’s effects extend to aquatic ecosystems as well. NOAA identifies harmful algal blooms as an escalating issue in the Great Lakes, exacerbated by higher water temperatures that foster rapid plankton growth. Casey Godwin, an associate research professor at the University of Michigan, emphasized the role of ice cover in protecting lake whitefish eggs, which may be compromised by milder winters linked to El Niño.
Despite international concerns about El Niño’s more severe impacts—such as flooding and drought in other regions—Illinois and the broader Midwest are expected to face relatively moderate effects. Ford cautioned that the warmer conditions could stress plants in gardens and landscapes by reducing soil moisture. Jesiolowski advised residents to water deeply and apply mulch or leaf litter to help retain moisture, recommending the conservation practice of leaving fallen leaves in place.
As temperatures begin to drop into the 40s, the natural cycle of fall color in the Chicago area continues to progress. At The Morton Arboretum, the slow but steady arrival of autumn hues offers a welcome respite amid broader global uncertainties.