Cloud Identification and Weather Prediction

Learn how to identify and interpret clouds to forecast weather in your area.


| May/June 2018


Every once in a while, you'll get a perfectly clear day — "not a cloud in the sky," as they say. While this makes for an ideal picnic setting, clouds have interesting stories to tell. Clouds are an integral part of the weather on earth. In many ways, they are the weather. Observant cloud watchers can even use them for forecasting.

How it all works

Clouds play a critical role in the Earth's water budget. Water evaporates primarily from the oceans and becomes water vapor in the atmosphere. To keep the cycle going, we need to get this water back down to Earth's surface. When air is cooled suf­ficiently, water vapor condenses into water droplets or ice crystals depending on the temperature. This is cloud formation. These droplets and ice crystals are so small that gravity is negligible and air currents keep them floating; therefore clouds don't fall to the ground. If the droplets or crystals become large enough, they fall in the form of rain, snow, or hail, thereby annoying some people but replenishing the Earth's water supply.

To produce the condensation that forms clouds, the air must be cooled. As pressure decreases with height, as air is lifted, it expands, and this causes a cooling effect. Cool air holds less water vapor than warm air, so eventually some of the water vapor condenses. Technically, condensation occurs when the air temperature reaches the dew point temperature.

The drop and lift

There are four major causes of "lifting" in the atmosphere and, therefore, four places we find cloud formation. "Orographic" lifting occurs when air is physically forced up over a topographic feature. Clouds are therefore prevalent in mountainous regions. When air heats, it rises. This is called "convection" and is common in many locations in the warm season. "Convergence" means that airflows meet or converge in one spot or along a line. If this happens near the surface, the air is forced to rise. Convergence is associated with low pressure areas, and lows typically have clouds.



"Fronts" are boundaries between relatively warmer and cooler air masses. With warm air being lighter, it typically rises over the cold air, and if moisture is present, clouds will form. Fronts typically have clouds due to this frontal lifting. Of course, once clouds form, they can move with the wind. Whether or not they dissipate (evaporate) depends on the amount of moisture in the air.

To a certain extent, you can use the clouds to forecast the weather. Long before there were professional meteorologists — and even today — people who spent a lot of time outdoors either developed this skill or it was passed down from previous generations. This is especially true of farmers, to whom weather is critical.

Denise
4/13/2018 9:10:02 AM

I would have loved pictorial examples of each type of cloud.








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