Sep 13, 2016 8:59 PM
Joe Knows: Season of change just a matter of time in NH
NH1 Chief Meteorologist
Even though we have not had our first widespread frost yet, it is just a matter of time. Before the month of September is through, the averages show we will likely have at least a morning or two with temperatures cold enough for frost to form. But, this has been a very warm summer, and the rest of September is not looking very cool. So we may be a bit late this year getting our first frost because of this mild pattern we are in. Either way, it will be happening sooner than later. Once we get that frost, the fall foliage season will be kicking into full speed.
There is no way around it. Temperatures start to drop as the days start getting shorter and the sun gets lower in the sky. The Sun does not warm the leaves as directly or as intensely as it did during the summer. Photosynthesis begins to break down and the Chlorophyll which helps to provide the green color to the leaves begins to evacuate the leaf. This exposes the other pigments like the reds, yellows and oranges in the leaf. An early frost can lessen the intensity of the reds. A hard freeze can help aid in the compromised or weakened leaves to fall from their trees a bit earlier than they would have otherwise.
If you can remember last year's foliage season was delayed by 1 to 2 weeks because of the warmth in the pattern from the developing Super El Nino which helped to bring our warmest winter on record! This warm pattern may give way to another delayed season this year. At the same time, the current severe-extreme drought has weakened and stressed the trees. This could mean a shortened foliage season which will come with a burst of color and could end quickly once at peak color with leaves falling from the trees.
Not all leaves turn vivid colors in the fall. Only a few of our many species of deciduous trees—notably maple, aspen, oak, and gum—produce stellar performances for our annual autumn spectacular in New Hampshire. Several factors contribute to fall color (temperature, precipitation, soil moisture), but the main agent is light, or actually the lack of it. Once the green is gone, two other pigments show their bright faces. These pigments, carotene (yellow) and anthocyanin (red), exist in the leaf all summer but are masked by the chlorophyll.