Areas of Excessive Rainfall; Watching for Tropical Cyclone Development in the Atlantic

Heavy to excessive rainfall Wednesday may bring areas of flash and urban flooding over portions of the Ohio and Tennessee Valleys. In Arizona and New Mexico, heavy to excessive rainfall from monsoon thunderstorms may bring isolated flash and urban flooding Thursday into Saturday. Two tropical waves in the Atlantic are being monitored for tropical cyclone formation within the next few days. Read More >

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Fall colors in this area of the country usually peak between the last week of September and the last week of October.

Visit the US Forest Service Fall Color webpage for a "Fall Colors Progression" map.

Why Do We See Different Colors in the Fall?
(Courtesy NWS Lincoln)

Many people think that cold weather is solely responsible for the color change in leaves, but not so. Leaves begin to turn before we have any frosts. Change in coloring is the result of chemical processes, which take place in the tree as the seasons change.

During the spring and summer, a food-making process takes place in the leaves, within cells containing the pigment chlorophyll. This gives the leaf its green color. The chlorophyll absorbs energy from sunlight, and uses it in transforming carbon dioxide and water to carbohydrates, such as sugars and starch.

In the fall, the decrease in intensity and duration of sunlight, and the cooler temperatures, cause the leaves to stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellowish colors or other pigments already in the leaf become visible.

Autumn weather conditions favoring the most brilliant colors are warm sunny days and cool, but not freezing, nights. A few hard frosts can cause the leaves to wither and fall from the tree without changing color. The degree of color may also vary from tree to tree. Leaves directly exposed to the sun may turn red, while those on the shady side may be yellow. When warm, cloudy and rainy weather dominates the fall season, leaves tend to have less coloration.

Fall colors usually peak from early to mid October over eastern Iowa and northwest Illinois, to late October in southeast Iowa, west central Illinois and northeast Missouri.


Images Courtesy, D. Becht, A. Gray, NWS DVN, and Missouri Department of Conservation

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