Rainfall is measured in terms of millimeters or inches, and, depending on the amount that has fallen, is usually described as light, moderate or heavy rain. It is said to be light rain if the amount totals one tenth of an inch of rainfall per hour. This type of rain is only a sprinkle, and doesn’t get you very wet if you get caught in it. You definitely wouldn’t need a raincoat during light rain. During a moderate rain shower, you would probably get wet if you spent even a short amount of time outside. You would definitely need a raincoat or umbrella to keep the water off your clothes and hair. Moderate rainfall measures from one tenth to one third of an inch of rain in an hour. Meteorologists call it heavy rain if more than a third of an inch of rain falls in an hour. The term, “it’s raining cats and dogs” applies here because there is nothing like a heavy shower to make you run for cover, and fast.
A simple rain gauge is a low-tech method of getting a rainfall measurement and all that is required is a container, such as a cylinder with a flat bottom and straight sides. While this type of container can help you gauge whether it was raining cats and dogs, it is very difficult to measure small amounts of precipitation this way.
In order to measure rainfall precisely, the gauge should be located out in the open and away from tall buildings, trees and any other obstructions. Inaccurate measurements are taken if the gauge is too close to large, impeding objects. The science behind the gauges isn’t totally precise, as water that is blowing or falling off of structures can enter the gauge, showing that it was raining cats and dogs when in actuality, it was only a moderate rain shower.