It happens every year at this time. At first it starts slowly, leaves on a branch or two change, then an isolated tree and finally swaths of color cover the landscape.

I’m talking, of course, about fall’s spectacle. It’s something that many people look forward to, and some people plan entire weekends or even vacations around its occurrence.

There is some predictability to when the leaves change, but the peak can vary by up to 10 days.  Last year’s peak, for example, was later than in previous years.

Peak color came after Columbus Day weekend in 2015

Peak color came after Columbus Day weekend in 2015.

Color varies widely from location to location.  The type of tree determines the color you will see, but the weather over the last year also plays a major role in how brilliant the colors will appear.  In some years the color is simply not as bright as others, but in no year will you not have the opportunity to view a wonderful display.

Both the prior weather and the upcoming weather affect the foliage season.  Other factors such as insects also have an impact on the colors.

Drought is a major factor this year, but the effect may not be all bad. One main purpose of leaves is to manufacture sugars. With the lack of rain in much of New England this spring, summer and fall, those sugars are more concentrated.

There are certain trees in which the concentration of sugar reacts to form chemical called anthocyanins. Certain maples and oaks as well as sumacs produce the highest amount of anthocyanins, and therefore display the most brilliant reds in the landscape.

Of course, not all leaves are red in the fall.

Carotene, along with chlorophyll, is also manufactured in leaves during the growing season. The shorter days and cooler temperatures cause the chlorophyll to break down and disappear.  Without the chlorophyll in the leaf, the remaining carotene causes the leaf to appear yellow.

Other factors to consider in the last year are the very mild December which, in combination with the February cold snap and cold spring, damaged many flower buds on the trees. Did you notice there were few or no maple seeds (spinners), this year? The flowers of the maple trees, like the peach trees, were damaged.

This means the energy of the tree was used in leaf production. The lack of rain has caused some trees to shed their leaves early or at least to change color, but these are mostly occurring in urban areas. The forests of northern New England still have less than 10 percent color change.

Gypsy moth defoliated the trees in some areas of far southern Maine, New Hampshire and parts of Massachusetts, so the new leaves that formed later in the summer likely won’t have as much color.

The best color occurs when the days are warm and sunny and the nights cool but above freezing.  With warmer than average weather predicted the rest of the month and considering the other factors, this year’s color should be intense, but the leaves will likely fall somewhat faster than usual due to the stress of the drought.

The warm weather last fall delayed foliage onset as compared to other recent years

The warm weather last fall delayed foliage onset as compared to other recent years.

Peak foliage season begins in northern Maine, New Hampshire and Vermont in the final days of September and then typically spreads south to southern New England throughout October and early November.

Columbus Day weekend often has some of the best overall color a short drive from Greater Portland.

Last year’s warm fall delayed the color onset compared with previous years; I think this year will be similar.