Weather Facts

How do you know when itís going to rain?

There must have been times when you see a big dark cloud move overhead and you say to yourself ěItís going to pourîÖ and nothing happens. Not all ědarkî clouds bring rain. There are certain signs that Mother Nature gives that normally precede a rain storm. There are some obvious indicators that rain is falling from an approaching cloud. Thunder and lightning is one of them. There are more subtle signs that rain is coming. When a cloud is producing moderate to heavy rainfall, the bottom of the cloud will appear smoother for a lack of a better word. In other words, you wonít see the outline of the individual clouds as well since the rain is obscuring the clouds themselves. On certain days, when you have good visibility overall and there are isolated rain showers or thundershowers, you will actually see the rain falling from the cloud. It will appear as a veil of gray extending from the base of the cumulonimbus cloud. Some folks claim that they can smell the rain coming. Now, we all know that when it first begins to rain, there is a certain smell that the ground emits. However, to smell rain before it begins is something that Iím not sure about. I think that folks are detecting the higher humidity levels that often transmit smells better. Another indication of rain, especially in the summer, is when the wind switches direction and increases rapidly. Heavy rain associated with thunderstorms cools the air through evaporational cooling and the cool air rushes downward as it is heavier than the warm air surrounding the storm. The air then rushes outward from the storm. The highest winds in a thunderstorm normally blow in the direction that the storm is moving. In other words, if you are southeast of an approaching thunderstorm that is moving southeastward, the northwesterly winds that precede the storm should be the strongest winds associated with the storm. Cloud patterns also can indicate that a steady rain is approaching. Sometimes the clouds appear like a herring bone pattern. This is usually a sign that rain or snow will occur within 24 to 36 hours. I will update this weather fact if I can think of more ěsigns of rainî. If you can think of any that I havenít mentioned, please e-mail me.