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Most leaves remain green, but the last few cool days have reminded us that peak season for fall foliage isn't that far off.Even without the recent cooldown, the rapidly dwindling daylight is a sign that autumn colors are on the horizon. When does fall color typically peak?Right now, we're still weeks away.On average, October is the month for prime viewing in Iowa — early in the month across the north and a few weeks later across the south. Upcoming weather will make a differenceLoss of daylight is the main driver behind leaves changing color each year. As nights get longer, leaves stop producing a green chemical called chlorophyll. When the green color disappears, other pigments like red, orange and yellow show through.Fall weather can influence this process.Sunny days and cool, crisp nights are best for producing vivid displays.Under these conditions, leaves produce lots of colorful sugars during the day, which become trapped within the leaves at night. Cooler temperatures also help break down the green-colored chlorophyll.Cool temperatures are helpful, but freezing temperatures are not.If leaves freeze before completing their color change, they're more likely to just drop off the tree prematurely.Past weather also mattersAccording to the U.S. Forest Service, the best fall colors often come when soils have received adequate moisture in the months leading up to autumn. That's something Iowa hasn't had the past few years, but this time looks different. Unlike many recent years, we started this September without widespread drought across the state. In addition, most of Iowa is coming off a wetter-than-normal summer. That wasn't the case in 2024, when precipitation was spottier. If we were coming into fall with a drought, it would depend on the drought's intensity. Moderately dry conditions can allow leaves to produce certain sugars more effectively and make some colors brighter.Severe drought often causes trees to go dormant early and drop their leaves right away.Current weather outlookDon't expect the current forecast to jumpstart color change in the leaves, though.Right now, a stretch of heat is expected for Iowa into the middle of September.Autumn warmth, especially at night, can slow down color changes in leaves and lead to duller hues. We're currently looking at 80-degree days and 60-degree nights for several days, and above normal warmth persisting into the third week of the month.