Tuesday, 18 June, 2013

Why do I feel colder on a damp day? © S.V. Medaris A damp, January morning brings hoarfrost to a Wisconsin farm. Let’s define a damp day as one with high relative humidity but without precipitation or fog. High relative humidity reduces evaporation, which can be dangerous in high temperatures. Although air temperatures are too [...]

Where does the dew on blades of grass come from? As fall begins, we have lots of mornings with dew on the grass. To explain this, we start with the fact that air contains water in the gas phase, called water vapor. Dew is made of liquid water that has condensed from that water vapor. [...]

What makes it feel “muggy”? See animation of NOAA’s Midwest Water Vapor Loop. Summer days are referred to as “muggy” when they are very warm and humid. The word “muggy” is believed to come from the Middle English “mugen” which means drizzle. It may also arise from the fact that on such a day, a [...]

How does fog form? Photo: NASA Fog is a cloud in contact with the ground. When the relative humidity approaches 100 percent, water vapor condenses on tiny particles suspended in the air to form a suspension of small water drops. The air in contact with the ground can reach high relative humidity if it cools [...]