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Why Peak Fall Foliage Could Be Delayed This Year
Published: September 14, 2019
Fall color will likely reach its peak later than usual this year across a large portion of the United States, and the weather is to blame.
By mid-September, some parts of the Rockies and northern tier often begin to see the early stages of fall color, eventually reaching a late-September peak in the Rockies' highest elevations, northern MInnesota and northern New England. Then, an early- or mid-October peak is typically found in the rest of the Rockies, Midwest, Appalachians and most of the Northeast.
(MAPS: Current Fall Foliage
Similar to last year, however, fall color is likely to run behind schedule again.
This is because much of the nation is predicted to have above-average temperatures in late September, according to the latest 8- to 14-day outlook from NOAA's Climate Prediction Center. Parts of the Northeast, Southeast, Rockies and West have at least 50-50 odds of warmer-than-average temperatures over the next one to two weeks.
8- to 14-Day Temperature Outlook
Warm, sunny days may be good for vibrant fall foliage, but only if accompanied by cool nights. This weather pattern should keep overnight lows rather mild for this time of year, which will likely cause the leaves to change color a week or so later than average, WBZ-TV chief meteorologist Eric Fisher, based in Boston, noted on Twitter.
After a wet summer for much of the U.S., most trees are healthy heading into fall – which officially begins Sept. 23 with the autumnal equinox – so leaf peepers should be in for an eye-popping show once the leaves do reach their peak, barring any tropical troubles that could make soils too saturated (heavy rain) or even strip trees of their leaves early (strong winds).
That said, dry conditions over some parts of the country could cause leaves to drop early and without much color.
How the Weather Impacts Fall Color
The weather before and during the time when chlorophyll in leaves decreases affects when leaves change and how vibrant their colors are, according to the U.S. Forest Service.
But the weather is just one factor that influences their color. The shorter amount of daylight is the primary trigger for the color change. As the nights become longer and colder, chlorophyll production slows and eventually stops. Without chlorophyll, the yellow and orange pigments of the leaves become dominant, resulting in the many beautiful colors of fall.
Warm, sunny days with cool nights are the ideal conditions for a colorful change. Soil moisture is also important. Both drought and excessive rainfall can be detrimental to a spectacular foliage season.
In the Mountain West, the higher peaks of Utah and Wyoming are seeing their first snow of the season this week. This may not be good for fall foliage in those areas because heavy, wet snow, which is common early in the season, can bring down trees or at least cause them to shed their leaves.
Even without snow, freezing temperatures destroy the ability of leaves to manufacture red and purple pigments. As a result, an early frost or freeze can cause leaves to fall from trees sooner.
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