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Name: Nicki R
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 6/4/2003


Question:
How does the temperatures during the day effect the cloudiness at night?


Replies:
This is a very complicated relationship. It depends on the moisture in the air, what fronts are moving through a given point, the elevation of the place, what is the relative amount of daylight and night time, whether it is sunny or cloudy during the day -- to name just a few variables. It would be almost impossible to factor all of those variables into a single answer.

Vince Calder


Dear Nicki- Surface temperatures do affect some kinds of clouds. But more important is how moist the air mass is. If a moist air mass is heated by the sun during the day, the warmed air rises in "bubbles" like bubbles in a pan of boiling water. When these bubbles rise far enough, the moisture condenses and clouds form. That's why many times, especially in the summertime, the sky is clear when you get up in the morning, but by noontime, many clouds have formed. Then, in the late afternoon, the sun does not heat the air as much, and the bubbles cease, and the clouds dissipate, and the sky is nearly clear again by dark. The same thing can happen day after day. Sometimes, if conditions are right, these bubbles can continue to rise, and rain showers, and even thunderstorms can form.

Many kinds of clouds can form other processes than the one I described above, processes not related to the daytime temperature.

Here is a link that briefly describes the different ways clouds can form.

http://www.geog.ouc.bc.ca/physgeog/contents/8e.html

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


Nicki,

The daytime temperature can affect nighttime cloudiness, but it is more often not a factor at all.

One example of the affect of daytime temperature is the disintegration of cumulus clouds as the Sun sets. The Sun's heating of the Earth's surface is reduced as the Sun goes down and convective cells of rising warm air (which form cumulus clouds) weaken. The cumulus clouds start decreasing in size and vertical extent and finally disappear after sunset.

Warm daytime temperatures can cause a layer of air to rise, giving you stratus clouds. If this layer is deep enough, the stratus clouds can maintain themselves into the night and even to sunrise.

Another possibility is for very cold conditions, where the daytime temperature is very low, but no clouds are present. Particularly if the air has a low amount of water vapor in it, further, strong radiational cooling at night can reduce the temperature of the air enough to produce thin stratoform clouds.

However, these situations are not as common as normal cloud forming processes associate with the presence of fronts, squall lines, etc., which are more dynamic in nature.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


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