When trying to predict the lowest temperature that will be reached overnight, forecasters pay close attention to the dew point temperature. Why is the air temperature unlikely to drop much below the dew point? (The high latent heat of vaporization of water is important.)

Meteorology, the science of the atmosphere, involves a plethora of parameters that give insight into weather patterns. One such crucial meteorological parameter is the dew point temperature, which provides vital information about atmospheric moisture content. Understanding the dew point helps meteorologists predict the formation of dew, frost, fog, or even precipitation.

Dew point signifies the temperature to which air must be cooled for water vapor to condense into liquid water, given the air pressure and humidity remain constant. It's a direct indicator of humidity; a higher dew point means more moisture in the air. Furthermore, it's valuable for predicting the lowest potential overnight temperatures, because as we'll see in later sections, the air is unlikely to cool below this threshold due to the principles involving the latent heat of vaporization.

The concept of latent heat of vaporization plays a pivotal role in understanding weather phenomena, including why temperatures seldom drop below the dew point. It refers to the energy absorbed or released during the phase change between the liquid and gas states of a substance—without changing the temperature.

For water, this energy is remarkably high; to transition from liquid to vapor, water must absorb a substantial amount of heat energy, and this very energy is liberated when the vapor condenses back into a liquid. The high latent heat of vaporization of water means that when airborne water vapor condenses—think of dew forming on the grass—it releases a significant amount of energy as heat into the surroundings, affecting local temperatures.

Humidity is a measure of the amount of water vapor present in the air. It's a key factor in both comfort levels and weather prediction. There are several ways to describe humidity, with relative humidity being the most common. It illustrates the amount of moisture the air contains relative to the maximum amount it could hold at that temperature.

Higher humidity typically means muggy conditions and can lead to a higher dew point. The relevance of humidity in meteorology cannot be overstressed; it impacts evaporation rates, heat indexes, and even the likelihood of rain. As the dew point is directly related to humidity, understanding this relationship is essential when estimating the lowest nighttime temperatures.

Condensation is the process by which water vapor in the air is transformed into liquid water. This change of state from gas to liquid occurs when the air is cooled to its dew point or when it comes into contact with a surface that is at or below the dew point. Common instances of condensation include dew formation on grass, water droplets on the outside of a cold beverage glass, and the fogging of glasses when you enter a warm building from the cold outside.

In the context of our previous discussion, when condensation happens, it releases latent heat, which helps explain why overnight temperatures often stabilize around the dew point. Since the process of condensation releases energy back into the air, it serves as a natural buffer against the air cooling down further, especially under clear sky conditions when radiation cooling would otherwise lower the temperatures substantially.