Weather, Leaves, and Fall Foliage (credit: How Stuff Works, ThoughtCo, Durango Train, The Weather Channel, Smoky Mountains)

Image:  Vibrant fall foliage - Credit ThoughtCo.

Discussion:  Fall is here and that means it’s time to say goodbye to green leaves. Already, some areas in the Northern Hemisphere are seeing changes in leaf foliage. Temperature, sunlight, and soil moisture are key factors that determine the boldness and vibrancy of fall leaf colors. Spring and fall weather are key. Since leaves grow in the spring, wetter springs are ideal. In the fall, warm and sunny days paired with cool and dry nights yield colorful leaf foliage. Soil moisture in the spring and summer can help increase chances for a picturesque fall, though summer weather itself does not have a substantial impact on the fall foliage.

Image:  Chlorophyll depicted in a leaf - Credit Smoky Mountains.

Chlorophyll is the plant molecule responsible for giving a leaf it’s green color. Leaves house other pigments as well,but chlorophyll masks them throughout most of the year. A shorter amount of daylight is the main cause for leaf color change. In the fall, when chlorophyll levels decrease, pigments of yellow by xanthophyll and orange by carotene are more visible. Photosynthesis is the process in which leaves interact with carbon dioxide and water to produce sugars and oxygen. When sugar is trapped in the leaf by the tree’s sealant, red and purple from anthocyanin pigment dominate. Cool nighttime air accompanied by daytime sunshine enhances red and purple colors.

Image:  Fall foliage - Credit ThoughtCo.

Leaves will fall before fully developing color if the growing season is dry, there is early frost, heavy rain, or extreme wind eventsin the fall. Elevation and latitude also affect how early the leaves change. High elevations such as Denver, CO and/or higher latitudes such as Boston, MA will see earlier peak times and therefore falling of leaves.

Image: Fall 2018 foliage peak times - Credit The Weather Channel.

The Weather Channel recently explained the typical peak of fall foliage across the Continental U.S. Overall, the leaves change quicker in higher latitudes and elevations. In late September or early October, fall colors reach their peak in the highly elevated Rockies, as well as northern Minnesota, northern Wisconsin, norther Michigan, northern Pennsylvania, upstate New York, and northern New England in higher latitudes. Fall colors typically peak in the second half of October throughout the western region, Midwest into the South, and the majority of the Northeast. Sometimes the mid-Atlantic and Southeast coasts and parts of the Deep South are slow to peak. If that is the case this year, the leaves will peak in early November.

Image:   Fallen leaves on the ground - Credit How Stuff Works.

Once this process is over, we usually forget about leaves until they bud again in the springtime. In actuality, leaves undergo a full cycle. After leaves fall, they decompose and create a rich humus, or dirt, on the ground that absorbs dew and rainfall. The fallen leaves are nutrient rich and act as sponges providing continual sources of nutrients and water to trees and other plants. In this way, leaves continually work as the life cycle ensures health and sustainability for trees until they sprout again the following spring.  
 
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© 2018 Meteorologist Amber Liggett