COLUMBIA, Mo. — Meteorologists have known for some time that rainfall forecasts have flaws, as failure to take into account factors such as evaporation 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, particularly for locations 30 miles or more from the nearest National Weather Service radar.
Dr. Neil Fox and doctoral student Quinn Pallardy used dual-polarization radar, which sends out two radar beams polarized horizontally and vertically, to differentiate between the sizes of raindrops. The size of a raindrop affects both its evaporation rate and its motion, with smaller raindrops evaporating more quickly but encountering 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, precisely determining how much evaporation would occur for any given raindrop.
The study, which you can read more about here, found that this method significantly improved the accuracy of rainfall estimates, especially in locations at least 30 miles from the nearest National Weather Service radar. Such areas often have large amounts of agriculture, and farmers depend on accurate rainfall estimates to manage their crops.
— University of Missouri
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