El Niño may delay and compress fall foliage in Chicago area

A strengthening El Niño, forecasted to be one of the strongest in over 75 years, may significantly impact the fall foliage season in the Chicago region. Experts at The Morton Arboretum are monitoring how the warming of the Pacific Ocean’s surface will influence local weather patterns.

According to Dr. Christy Rollinson, a senior scientist in forest ecology at the Arboretum, the warming impact of El Niño could lead to a compressed fall color season, with leaves changing rapidly all at once in late fall. While summer droughts typically trigger earlier color changes, recent data from the Illinois State Climatology Office indicates that higher-than-average precipitation over the last 90 days has offset those effects.

National Weather Service data suggests above-average temperatures for October, November, and December. If these warmer conditions persist, they are expected to delay autumn colors generally. However, once the region experiences several consecutive nights of freezing temperatures, the color change is expected to occur quickly.