The rain gauge most often used by airports and officials forecasters consists of four main components which include a large cylinder, a funnel, a measuring tube and a measuring stick. The cylinder houses a funnel that sits at the top and collects rain water as it falls. The funnel channels the rain water into a measuring tube which is also housed in the cylinder. The measuring tube is designed with exactly one-tenth the cross sectional area as the width of the top of the funnel. The measuring tube is minimized to account for the exaggeration of the height of the water, so that more precise measurements are possible. For example, 1 inch of water in the measuring tube is actually only one-tenth of an inch of rainfall. Rain gauges measure up to 1 inch of rain water inside the tube before the water overflows into the surrounding cylinder. To retrieve an accurate rainfall measurement, the water in the measuring tube is emptied and the water from the cylinder is poured in, one inch at a time. Meteorologists use a special measuring stick that they insert into the measuring tube for readings that are accurate to within one-hundredth of an inch.
Rain gauges work to assist meteorologists and other observers in determining how much rain any given area receives. Knowing the amount of rainfall helps predict flooding, flash flooding or drought conditions that impacts everyone. The local weather reports do not offer the most accurate rainfall measurements for every homeowner or farmer in a given area. Rainfall can vary significantly from one neighborhood to another, even if they are adjacent. Personal rain gauges work to measure the amount of rainfall in a specific location. There are varieties of rain gauges commercially available to help individuals measure the amount of rainfall on their property. These gauges may be simple tubes with measurement indications or more complicated instruments with weigh the rain water.
Rain gauges can also work for measuring other types of precipitation, such as snow or hail. To accurately measure other precipitation, observers remove the inner measuring tube and the funnel and allow the ice and snow to collect in the outer cylinder. The material is melted and poured into the measuring tube for a final measurement. The amount of precipitation determined by a rain gauge does not equal the amount of snowfall. Snow to water ratios can vary from less than 8:1 or more than 20:1.