Weather Science

Rochester’s mild drought didn’t affect the fall foliage! How temperature and rainfall affect leaf colors.

Before you venture out apple picking this fall, be sure to have your camera on standby as the vibrant upstate New York foliage is predicted to be as spectacular as ever this year. Many Rochesterians were able to experience the beginning of the foliage season this weekend, especially apple pickers who flocked to festivals all over the area such as the 32nd annual Hilton Apple Fest held at Hilton Apple Fest Farm Market.
It has been a disappointing season for apple pickers this autumn due to the significant decrease in production. Although many apple farms have been at a loss of words with the notable decline in apples this year, people all over the region will be able to enjoy the brilliant colors of autumn as peak hits this next week.

Some speculated that the dry conditions we have seen in Upstate New York will have a negative impact on the foliage this fall, however as you may have already noticed, that is far from the truth.

Map of the height of this summer’s drought, via the University of Nebraska’s Drought Watch

Over the past four months or so, upstate New York has been entrenched in a moderate drought, which has led to an increase in food prices and distraught flowers. Along with these impacts, many New Yorkers expressed their concern over the lack of vibrant colors they would see due to the drought. However, Donald Leopold, chairman of environmental and forest biology at SUNY College of Environmental Science and Forestry, explains that drought is not always bad for foliage: “Mild droughts are generally good for fall leaf color. It can enhance production of certain pigments in leaves that produce color”.

An example of the “scorching” that occurs in leaves when the environment is too hot and dry. Via

It’s common sense that trees need the necessary water and sunlight to survive: this beautiful concept is known as photosynthesis. But too much rain or sunlight throughout the spring and summer could have a negative impact on the health of the tree and more importantly, the leaves.
According to meteorologist David Epstein, an abundance of precipitation can encourage disease on the leaves, creating dull or bland colors. While not enough precipitation causes the leaves to dry up and fall early, not allowing for colorful leaves. Luckily, our moderate drought was not severe enough to have a negative affect on the foliage.

As for temperatures, colder temperatures, especially at night, breaks down chlorophyll in the leaves, exposing the red and orange pigments we are so accustomed to during autumn. On the other hand, warmer temperatures don’t allow for this breakdown in chlorophyll, creating delay in pigments and accordingly delay in foliage change.

Regions such as the Midwest have not been as lucky as we have this fall. A persistent severe drought has not only killed the economy of the Midwest but foliage is almost nonexistent this autumn, thanks to the drought. Rochesterians should cherish this falls’ colors, as you never know what next fall brings.

Rochester Weather Science

Bundle up! How dew point affects temperature as Rochester chills for fall.

As seasons change and days become shorter, Rochesterians begin to brace themselves for another long winter. Opening the front door on an early fall morning, you may expect familiar summer air only to be rudely welcomed by a blanket of frost.

Long before winter makes her presence felt on the northeast, the transition into fall not only brings the beauty of radiant deciduous trees but also the cool, crisp air of autumn.  Did you ever wonder why during this period, daytime temperatures may still climb into the 80s but come nightfall, temperatures dip well into the 40s? Or in a matter of minutes following sunset, temperatures will drop ten or almost twenty degrees?

This is a direct result of a decrease of daily dew point temperatures. The dew point temperature is the temperature at which the air needs to cool to reach saturation. What does this mean? Essentially, dew point temperature is the measure of water vapor or moisture in the air. To grasp the idea of dew point temperature, think back two months to the unbearably muggy days of July. At some point everyone has said, “It’s way too hot outside”. Hot temperatures are exacerbated by exceptionally high dew point temperatures (approximately 65° and greater) not allowing perspiration or sweat to evaporate efficiently, which creates an oppressively hot, sticky feeling.

This week, Rochesterians have begun to experience “fall” like weather, especially in the mornings. Sure colder temperatures are associated with this feeling.  However, fall brings a certain crisp, dry air, allowing more evaporation of perspiration, and thus comfortable conditions.

Since the dew point temperature is the temperature at which air needs to cool to reach saturation, it is important to note that temperature cannot be lower than dew point temperature. Thus, one can use this fact to help predict the low temperature for a given day.  When the sun sets and earth cools due to lack of incoming solar radiation (heat from sun), the temperature will usually cool to around the dew point temperature. This is why lows in the summer often stay in the mid 60s or even 70s while lows in early autumn will drop into the 40s or below.

Dew point temperature and air temperature can be equal to one another though, which results in 100% relative humidity causing the air to condense and form early morning dew. As fall progresses, temperatures continue to drop, along with the dew point temperature, eventually falling below the freezing mark (32°F).  When the relative humidity is 100% and the temperature is below freezing, water in the air deposits on the ground as frost.

When frost coats the ground for the first time in autumn, it’s a sure thing that beach season has come to an unfortunate end.