The Weather Wise column has been asked to settle a family feud. It concerns when tree leaves begin changing colors in Indiana and what causes the change.
Question: Some people in my family claim trees turn color earlier in northern Indiana. Our cousins in southern Indiana say they turn earlier in southern Indiana. Who is right, and how does weather affect when trees turn color?
Answer: The northern half of the state usually turns color first. The main reason behind this is that the changing of leaves is triggered by shortening daylight hours and temperature change. The U.S. Forest Service states warm, sunny days followed by cool but not freezing nights are best for producing the most brilliant colors.
There are other factors such as soil moisture that can affect the colors, as well. Spring or summer droughts can delay coloring of leaves, and warmer-than-normal temperatures can lower the intensity of fall colors.
Shorter daylight hours and weaker solar radiation trigger the trees to begin limiting fluid supply to their leaves. The trees do this to prepare for winter dormancy. When veins in leaves close, sugars get trapped in the leaves. The sugars produce chemicals that trigger the vibrant fall colors.
Eggert works in the Indiana State Climate Office. He writes from West Lafayette.
WHEN COLORS CHANGE: This map depicts when you can expect trees to begin changing colors across the country. Notice where the break in timing falls in Indiana.