3 Weather Phenomena You'll Only See if You're an Earlybird or Nightowl

Weather is usually something that we actively experience (see and feel) occurring. But there are some weather phenomena whose occurrence would go undetected if not for the visual evidence that lingers (for several hours only) after the fact.

Here's a look at three such weather events, each one which occurs while most of the world is sleeping and dissipates shortly after the world (and the sun) awakens.

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Dew

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Dew forms in the nighttime hours. After the humidity (water vapor) in the air condenses into droplets of moisture we call dew. after the air temperature has cooled (link to diurnal . Dew is rare in that it's the only weather process by which water forms onto object surfaces rather than directly in air (like fog, clouds, and rain do). 

Since warmer air has more capacity for water vapor and cooler nights are needed to cool the air, this is why you'll usually see dew in the late spring and early fall (times of year when cool nights following warm days is typical).

By mid-morning, dew drops have only linger until the mid-morning. By this time, the sun has warmed the air enough that the dew evaporates back into water vapor.

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Frost

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Like dew, frost also forms on calm nights, except requires that the dewpoint temperature (and air temperature) be below freezing. It forms when a solid surface cools below the dew point of adjacent air, and below freezing (32°F / 0°C). Because of this, frost is considered to be a fall and spring event.

Frost is an example of deposition -- meaning water vapor changes directly from a gas into a solid (without entering the liquid state). 

03
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Fog

morning fog.jpg
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Radiation (ground) fog forms on clear, cool nights when humidity is fairly high. On such nights, the ground and the air immediately above it cool rapidly. Because the relative humidity is high, just a small amount of cooling will lower the air temperature to the dewpoint and cause fog to form. (Radiation fog takes it's name from this process of heat radiating away from the ground back out into space.)

Again, because fog formation favor the cool nights and mornings that follow mild days, fall tends to be a fairly foggy time of year.

In the winter, you may hear of two other types of fog, freezing fog and ice fog. Freezing fog works on a similar premise to freezing rain; the fog droplets are supercooled liquid droplets that freeze onto surfaces they come into contact with, covering them in rime ice. In contrast, ice fog refers to fog where the droplets have frozen into tiny ice crystals. As you can imagine, it takes some pretty cold temperatures to suspend ice in midair -- roughly -31 °F (-35 °C) or below to be exact! For this reason, ice fog is generally only seen near the Arctic and Antarctic regions.

In the winter, you may hear of two other types of fog, freezing fog and ice fog. Freezing fog works on a similar premise to freezing rain; the fog droplets are supercooled liquid droplets that freeze onto surfaces they come into contact with, covering them in rime ice. In contrast, ice fog refers to fog where the droplets have frozen into tiny ice crystals. As you can imagine, it takes some pretty cold temperatures to suspend ice in midair -- roughly -31 °F (-35 °C) or below to be exact! For this reason, ice fog is generally only seen near the Arctic and Antarctic regions.