Weather FAQ

Curious about the weather or weather-related terminology? Ask our experts those burning questions; we'll add the ones we believe to be of general interest to the public to this list.

What is Relative Humidity?

Relative Humidity is defined as the ratio of the quantity of water vapor in the atmosphere compared to the capacity of the atmosphere to hold water vapor. The capacity of the atmosphere to hold water vapor is temperature-dependent, generally increasing as the temperature increases.

Atmospheric humidity may be determined using an instrument called a psychrometer which measures values known as dry-bulb and wet-bulb temperatures. From these values, the relative humidity may be derived.

What is the dew point, and what is its significance in a forecast?

The dew point is a direct measurement of the moisture in the air, the temperature at which water can readily condense out of the air to form dew. As the moisture increases in the atmosphere so does the dew point. When the dew point and the air temperature are equal, the air is saturated. (This means that the humidity is 100%). The significance to the forecast is that we can tell what the heat index will be, what the potential for showers will be, and in the winter, if we will have frost or freezes.

What is the vernal (spring) or autumnal (fall) equinox? What is a solstice?

The Earth's axis is tilted with respect to the plane of its orbit. Excluding the small, slow wobble known as precession, the tilt remains constant along the whole path around the sun. For most of the year, this means that one of the poles will be tilted toward the sun, while the other pole is tilted away.

The equinoxes are the only two positions along Earth's orbit where neither the North or South pole is tilted toward the sun, each pole receiving equal amounts of light. These points in Earth's orbit mark the transitions into Spring and Fall.

The solstices are those points in the orbit where either the North or South pole is tilted maximally toward the sun. These points mark the transitions into Summer and Winter.