"Tomorrow, expect scattered clouds in the morning with an overcast sky in the
afternoon and a 60% chance of rain." Huh? What does a weather
forecaster mean when he/she makes that kind of statement?
Well, that statement concerns something meteorologists call "sky conditions."
Sky conditions consist of two main areas: cloud
cover and probability of precipitation.
Probability of precipitation is the likelihood that it will rain, snow, sleet,
or hail. Meteorologists use several instruments and scientific calculations to
figure out this probability.
Cloud cover is based on observations more than calculations. Cloud cover is the
amount of sky that is covered by clouds. The following table describes the
different levels of cloud cover and the meanings.
|Cloud Cover Term
||10% of the sky is covered by clouds
||10%-50% of the sky is covered by clouds
||50%-90% of the sky is covered by clouds
||>90% of the sky is covered by clouds
||sky is covered by fog, smoke, blowing snow, or smog
Sometimes, a meteorologist refers to the cloud deck. Cloud deck is the
height from the Earth's surface to the bottom (base) of the cloud. There can be several cloud
decks, just like the decks of a cruise ship. Each cloud deck may represent a
type of cloud, such as High Clouds, Middle Clouds, or Low Clouds.
If the sky is broken or overcast, then you can usually only see the lowest cloud
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