October 12, 2000
Meteorologists do a lot more than just look up at the clouds. Weather forecasting is a very complex business; it uses satellites, doppler weather radar, upper atmosphere balloons, and computer data. With all these tools available, there is still no substitute for going outside and to taking a look at the sky. The clouds we see there can tell us a great deal about future weather conditions -- in some cases, several days in advance. One example is the very high and thickening cirrus clouds that sometimes precede low-pressure storm systems by a day or so. The appearance of cirrus clouds can indicate a chance of precipitation several days in advance. These high clouds can produce solar and/or lunar halos, so the old tales about a "ring" appearing around the moon or sun indicating approaching rain can sometimes be correct!
Sometimes billowing cumulus clouds can be observed during the midday hours. These clouds indicate an unstable atmosphere -- an atmosphere where the air rises (that is the way our atmosphere produces clouds and precipitation). As the day progresses, these cumulus clouds can develop into cumulonimbus clouds, the clouds that produce thunderstorms and heavy rain.
Fog and low stratus clouds seen during the winter and spring months indicate a stable atmosphere. Many days when these clouds are present during the morning hours, when the Sun heats the atmosphere, these clouds "burn off" to leave a fine, sunny day.
To learn more about clouds, see the "Clouds and Precipitation" learning module at http://www.lamc.utexas.edu/kimmel/.