New method makes weather forecasting more accurate

A new method using modern radar capabilities could make weather forecasting much more accurate. The method can account for evaporation.

Rainfall forecasts are often flawed due to their failure to take into account factors such as evaporation that can affect their accuracy.

Now, researchers from the University of Missouri have developed a system that improves the precision of forecasts by accounting for evaporation in rainfall estimates, announced a statement.

“Right now, forecasts are generally not accounting for what happens to a raindrop after it is picked up by radar,” explained Neil Fox, associate professor of atmospheric science. “Evaporation has a substantial impact on the amount of rainfall that actually reaches the ground.”

The new method harnesses dual-polarization radar, which differentiates between the sizes of raindrops by sending out two radar beams polarized horizontally and vertically. Because the size of a raindrop affects both its evaporation rate and its motion, smaller raindrops evaporate more quickly but encounter less air resistance.

By combining this information with a model that assessed the humidity of the atmosphere, the researchers were able to develop a tracing method that followed raindrops from the point when they were observed by the radar to when they hit the ground, thus enabling them to precisely determine how much evaporation would occur for any given raindrop.

Their method significantly improved the accuracy of rainfall estimates, especially in locations at least 30 miles from the nearest National Weather Service radar.

Fox added that more accurate rainfall estimates would be beneficial to farmers in these areas. He explained: “Many of the areas that are further from the radar have a lot of agriculture. Farmers depend on rainfall estimates to help them manage their crops, so the more accurate we can make forecasts, the more those forecasts can benefit the people who rely on them.”

Fox said more accurate rainfall estimates also contribute to better weather forecasts in general, as rainfall can affect storm behavior, air quality and a variety of other weather factors.

The study was published in the Journal of Hydrology with funding provided by the National Science Foundation.

Photo credit: Michael Moore/ CC BY-NC-ND 2.0

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