Sky Conditions

"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 Meaning
Clear 10% of the sky is covered by clouds
Scattered/Partly Cloudy 10%-50% of the sky is covered by clouds
Broken/Mostly Cloudy 50%-90% of the sky is covered by clouds
Overcast >90% of the sky is covered by clouds
Obscured 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 deck.

Try an Experiment

Last modified April 9, 2001 by Jennifer Bergman.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

High Clouds

The high cloud group consists of Cirrus, Cirrostratus, and Cirrocumulus clouds. High clouds are made of ice crystals due to the cold air in the upper sky. The base of a high cloud above the surface can...more

Middle Clouds

The middle cloud group consists of Altostratus and Altocumulus clouds. Middle clouds are made of ice crystals and water droplets. The base of a middle cloud above the surface can be anywhere from 200...more

Low Clouds

The low cloud group consists of Stratus, Stratocumulus, and Nimbostratus clouds. Low clouds consist of water droplets. The base of a low cloud is from the ground surface to 2000m....more

Watch the Sky

Ever looked up in the sky on a lazy Sunday afternoon and just watched the clouds? Well, here's a project where you can do just that and learn something too! This project works best if you do it with a...more


Altocumulus clouds are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups and are about...more


Altostratus belong to the Middle Cloud group (2000-7000m up). An altostratus cloud usually covers the whole sky and has a gray or blue-gray appearance. The sun or moon may shine through an altostratus...more


Cirrocumulus clouds belong to the High Cloud group (5000-13000m). They are small rounded puffs that usually appear in long rows. Cirrocumulus are usually white, but sometimes appear gray. Cirrocumulus...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA