Fall leaves are about to get less colourful

If you live on the East Coast and are counting down the days until the crispness of fall finally sets in, you’ll have to be patient.

The autumn forecast for the US indicates that the season’s temperatures will be far above average in the Northwest and Mid-Atlantic, with few of the usual cold bursts that pepper the early fall months. In the Midwest, the beginning of the new season is also expected to feel like an extension of summer — temperatures could still creep into the 90s during September.

Those warm temperatures might be nice for fall camping trips and last-gasp trips to the beach, but they also mean that fall foliage will likely be less vibrant this year than it has been in the past, according to Accuweather.

That’s because, although changing autumn colours are primarily driven by the shortening of daylight hours, the temperature affects the degree to which trees take on those bright oranges and reds.

As night length increases during the fall, leaves slow down their production of chlorophyll, which is used in photosynthesis and naturally breaks down with exposure to light. Chlorophyll is also what makes leaves appear green, so once it disappears, other pigments — xanthophylls, carotenoids and anthocyanins — can become visible.

The ideal recipe for brilliant colours is a combination of sunny fall days and cool nights — that causes the chlorophyll to be destroyed more quickly while promoting the formation of anthocyanin, which give leaves their deep red and purple colours.

But with temperatures staying high along the east coast, nights will likely not get sufficiently cold in time to get rid of enough chlorophyll to properly augment the leaves’ colours.

That will be especially true in the Northeast and will impact the Mid-Atlantic as well, so residents of states known for their beautiful foliage, like Pennsylvania, New York and New Hampshire, might prove disappointing for leaf peepers.

The bright side, however, is that East Coasters will probably get to enjoy more summer weather before they have to pull out their jackets and scarves.

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