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October 6, 2010 / Dave Gorham

Fall’s Annual Explosion of Colors…It’s Here!

Fall is my favorite time of the year and I can think of several reasons why. Okay, I’ll admit one of those reasons is football season, but otherwise it’s completely weather related. I love it when the temperatures start to fall and you wake up to a cool, fall morning. For the past several days I’ve actually needed a lightweight jacket in the mornings with temperatures in the Houston area dropping into the 50’s. Another thing I look forward to is the fall foliage. Granted, some areas have better fall foliage than others. Call me a little biased since I’m from Alabama (the Birmingham area), but I think it’s beautiful there this time of year.

Alabama fall foliage. Bursts of red, yellow and orange dominate here and the peak of the fall colors in northern Alabama is typically late October into early November. Photo: Birmingham News

The weather plays a major role in how bright the leaves’ colors are during fall with temperature and moisture the main influences. Weather conditions both before and during the time chlorophyll starts decreasing in the leaves is crucial. During the growing season, chlorophyll is constantly produced and broken down easily in sunlight. This is what makes and keeps the leaves green all summer long. As fall arrives and the nights get longer and cooler, the production of chlorophyll slows down and eventually stops as the trees prepare for winter. This allows the carotenoids and anthocyanins in the leaves to be unmasked and show their true colors.

The most brilliant fall colors tend to come from warm, sunny days and cool nights. The warm days allow sugars to be produced in the leaf but the cool nights prevent these sugars from moving out. Lots of sugar and sunlight produce the anthocyanin pigments which give the leaves their radiant colors (i.e. reds, purples, etc.). The amount of moisture in the soil also affects the colors. The best weather conditions for a dazzling array of fall foliage would come from a warm and wet spring/summer and warm, sunny fall days with cool nights. On the other hand, when an area suffers from a lack of moisture in the soil or an actual drought, this can often delay the arrival of fall colors a few weeks.

The U.S. Drought Monitor. Image: Drought Monitor

According to the U.S. Drought Monitor, a good portion of the eastern U.S. and portions of the Rockies have been abnormally dry this year. Parts of northern Louisiana, eastern Alabama and eastern West Virginia are currently in an extreme drought (indicated in red). It appears with the hotter-than-average summer across the eastern and southern U.S. combined with the abnormally dry/drought conditions some areas have seen this year, this could delay the onset of fall foliage across this region.

Hopefully the spectacular colors of fall will show their true colors this year across the eastern U.S. as this is where the majority of America’s best foliage appears. New England always has beautiful fall foliage and this year is no different. Some areas across Maine, Vermont, New Hampshire and Massachusetts are currently reaching their peak as they tend to see their leaves change colors beginning in September.

Areas in red indicate where they’re reaching peak fall foliage. Image: Yankee Foliage

For the most part, in Houston we don’t get to experience the beautiful fall foliage other parts of the south get to experience. This is because our trees are mostly evergreens and our climate is humid subtropical. Here at ImpactWeather, we’re only 36 miles from the Gulf Coast in Galveston. So it looks like I’ll be sneaking off to Birmingham at the end of the month to enjoy the fall foliage.

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