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Fixing the flaws of forecasting

Researchers from the University of Missouri are working on improving the accuracy of rainfall forecasts for meteorologists. (KTVO:Riley Fannon)

Courtesy of MU News Bureau and Austin Fitzgerald

Will it rain? And how much will we get?

Two questions we get asked quite a lot as meteorologists. For us, tracking a storm and determining when it will hit the Heartland is a simpler prospect compared to forecasting rainfall amounts.

Rainfall forecasts have flaws, as failure to take into account factors such as evaporation can affect accuracy. Researchers from the University of Missouri are developing a system to improve our forecasting precision. Neil Fox, associate professor of atmospheric science at MU, and doctoral student Quinn Pallardy have been using dual-polarization or dual-pol radar to conduct their research.

Right now, forecasts are generally not accounting for what happens to a raindrop after it is picked up by radar," Fox said. "Evaporation has a substantial impact on the amount of rainfall that actually reaches the ground. By measuring that impact, we can produce more accurate forecasts that give farmers, agriculture specialists and the public the information they need.

Using two radar beams that read the atmospheric conditions both horizontally and vertically they are able to tell sizes of raindrops. And size matters for rainfall amounts. As the size will affect the evaporation rate as well as the motion of the raindrop as it falls. Combining this data with a computer model that details the humidity in the atmosphere, Fox and Pallardy were able to generate a tracing method.

This method follows a raindrop from point of first observation to when they hit the ground. They found this method significantly improved the accuracy of rainfall estimates, more so in locations at least 30 miles from the nearest National Weather Service radar. The radar beam will rise higher into the atmosphere as they travel, something which affects the Heartland constantly. The higher the beams are in the atmosphere, the less accurate it becomes because it observes raindrops that have not yet evaporated.

"Many of the areas that are farther from the radar have a lot of agriculture," said Fox. "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 those people."

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

Their study was published in the Journal of Hydrology and will continue to be experimented with to create as accurate a forecast model as possible.

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