Weather Savvy
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How Do Clouds Affect the Temperature?

Clouds have a tremendous impact on the temperature at the surface and that makes clouds a big player when it comes to forecasting.

The reason clouds are so important is because they have the potential to block our source of heat, the sun. The majority of our atmosphere's warming is due to the sun's heat energy reaching the surface of the earth.

Sunlight "short-wave" energy is absorbed by the earth's surface and then a different type of energy "long-wave" energy is emitted by the earth back into the air. This type of "long-wave" energy is absorbed by gases in the air called greenhouse gases. Without these gases our atmosphere would be too cold to support life.

Now that you understand how our atmosphere absorbs heat energy, you'll easily understand how clouds affect the temperature at the surface.

The obvious result with a lot of cloud cover or overcast skies is that the sunlight energy is reflected back out to space or even absorbed by the clouds. With less sunlight reaching the surface, the temperature will have a tough time warming up.

But clouds are porous, meaning they can't block 100% of the sun's energy. That's why even on a cloudy day temperatures warm even a little bit. As an example, in the Midwest of the US where I live, when we have an overcast day with no breaks in the clouds ( I call it being socked in) the temperature will usually warm about 4 to 7 degrees from the morning low. On a typical day with partly cloudy skies, the temperature will warm 20 to 30 degrees from the morning low (depending on what other forces are affecting weather that day). So, you can see how the clouds have a tremendous affect on temperature.

Something you might forget is that clouds, or lack of clouds, during the nighttime also has a big impact on temperature. However, at night we don't have the sunshine, so where is the heat coming from?

During the night the heat absorbed by earth during the day continues to be emitted from earth to the air. And with no cloud cover, this heat will rise and rise and rise...eventually out to space. This leaves the surface cold, because the heat is rising out to space. Typically on clear nights with little wind, you get those very cold and sometimes record low temperatures.

However, with cloudy skies at night the clouds can act like a blanket trapping some heat between the clouds and the surface. Thus, you end up with a more mild morning low temperature.

I should note that all these examples are assuming no cold fronts, warm fronts or anything else is drastically changing the weather conditions.