New method makes weather forecasts right as rain

June 12, 2018, University of Missouri-Columbia
Credit: CC0 Public Domain

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.

"Right now, forecasts are generally not accounting for what happens to a raindrop after it is picked up by ," said Neil Fox, associate professor of atmospheric science in the School of Natural Resources at MU. "Evaporation has a substantial impact on the amount of 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."

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 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.

Credit: University of Missouri-Columbia

Researchers 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. Radar beams rise higher into the atmosphere as they travel, and as a result, radar that does not account for evaporation becomes less accurate at greater distances because it observes raindrops that have not yet evaporated.

"Many of the areas that are further from the radar have a lot of agriculture," Fox said. "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, "Accounting for rainfall evaporation using dual-polarization radar and mesoscale model data," was published in the Journal of Hydrology.

Explore further: NASA peers into the rainfall of Eastern Pacific' Tropical Storm Aletta

More information: Quinn Pallardy et al. Accounting for rainfall evaporation using dual-polarization radar and mesoscale model data, Journal of Hydrology (2017). DOI: 10.1016/j.jhydrol.2017.12.058

Related Stories

Higher temperature, heavier rain

May 14, 2018

An evaluation of weather radar measurements reveals that in the eastern Mediterranean the total amount of rain decreases with increasing temperatures. But while storms are weakening, convective rain cells – the chief cause ...

GPM data used to evaluate Hawaii's flooding rainfall

April 19, 2018

A weather system moving slowly westward through the northwestern Hawaiian Islands has caused destructive flooding and mudslides and NASA's Global Precipitation Measurement mission or GPM satellite analyzed the heavy rainfall.

Recommended for you

Life cycle of sulphur predicts location of valuable minerals

October 23, 2018

A team of researchers from The University of Western Australia and two Canadian universities has applied a first-of-its-kind technique that measures the long-term life cycle of sulphur, helping to explain the preferential ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.