October opens with an autumn chill here in Georgia but the month as a whole looks to average out with near-normal temperatures and rainfall normal to below unless we get a tropical hit. November looks to average out near-normal to a tad below-normal on temperatures with below-normal rainfall.

Many weather factors play into how intense the colors will be and how long the leaves will be around and in good color.

After the leaves are fully developed on trees, they begin making and storing the carbohydrates that will be needed for new tree growth. As the season progresses, in early fall, the trees enter a growth process that produces the colorful fall leaves, according to the U.S. Dept. of Agriculture.

As a tree grows throughout the spring and summer months, chlorophyll is constantly replaced in the leaves. The chlorophyll gives the leaves their green color.

As the nights get longer in the early fall, the cells near the juncture of the leaf and stem divide rapidly but do not expand. This action of the cells form a layer called the abscission layer. The abscission layer then blocks the the transportation of materials from the leaf to the branch and from the roots to the leaves. As the chlorophyll is blocked from the leaves, it disappears completely from them.

The lack of chlorophyll allows the yellow (xanthophylls) and orange (carotenoids) pigments to be visible. The red and purple pigments (anthocyanins) are manufactured from the sugars that are trapped in the leaf. These pigments in leaves are responsible for the vivid color changes in the fall.

The weather before and during the autumn is key to how the leaves will look in the fall.

• Abundant sunlight and low temperatures after the abscission layer forms cause the chlorophyll to be destroyed more rapidly leading to quick change.
• Cool air (especially at night) with a lot of daytime sunshine promote the formation of more red and purple pigments.
• Freezing conditions destroy the leaf's ability to manufacture the red and purple pigments. Early frost will end the colorful foliage.
• Drought during the growing season can cause the abscission layer to form early and cause the leaves to drop before they change color or with muted colors and leaf drop simultaneously.
• The best weather for brilliant fall foliage is a growing season with ample moisture (good spring and summer rains--no drought) followed by a dry, cool and sunny autumn with warm days and cool but frostless nights.
• Heavy wind or rain can cause the leaves to fall before they fully develop color.

Usually, a good year for a colorful display would be a good climatic growing season without prolonged drought. However, that's only one part of what makes a great year for brightly colored leaves.

Really, one of the most important things is what happens in October.

Crisp temperatures are the key for brightly colored leaves. In those weeks, nighttime temperatures hopefully fall into low 30s and 40s with bright sunny days and dry weather.

Warm and wet would be a problem because the leaves won't go into their normal coloration.

The leaves are brightest when the cool weather starts at the end of September. If the cool down starts in late October or November instead, the colors aren't as vibrant.

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