Forecasting Summertime Thunderstorms Improves

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Get a heads up on pop-up storms
before there's rain to see on radar

HUNTSVILLE, Ala. (June 10, 2013) — Using a tool developed at The University of Alabama in Huntsville (UAH), meteorologists in the continental U.S. now can get an advance warning of pop-up spring and summer storms before they pop up on radar.

Using data from weather satellites, the UAH program can predict which puffy clouds are most likely to produce rain and lightning in the next 30 minutes to two hours. Regional real-time, current satellite images showing these "nowcasts" are available online at nsstc.uah.edu/SATCAST/.

"We expect that many people in the industry might be interested in using this resource," said John Mecikalski, the SATCAST project director and an associate professor of atmospheric science in the Earth System Science Center at UAH. "It might be useful, for instance, to be able to provide this information to people in the construction industry, or to farmers thinking about spreading chemicals on their fields, or to people who organize and put on outdoor events and concerts.

"Basically, we tried to make this site useful for anyone who could benefit from knowing in advance how likely it is that a thunderstorm might develop and move over where they are."

While the National Weather Service's Doppler radar network provides reliable data on the location and intensity of rain once it starts falling,  models used to forecast when and where convective storms might start producing rain have are not been very accurate in forecasting either the exact locations or the timing of thunderstorms.

The SATCAST (the Satellite Convection Analysis and Tracking system) uses data from National Oceanic and Atmospheric Administration GOES weather satellites to monitor cumulus clouds as they develop, move and grow before they become thunderstorms.

During the system's 10-year development, UAHuntsville scientists learned that important factors in predicting thunderstorm formation are temperature change in cloud tops, how strong the updraft is within the cloud, and determining when water vapor in the tops of cumulus clouds turns to ice. These can be monitored using multiple satellite sensor channels.

The temperature at the top of a cloud is related to its altitude, with temperature dropping as you go higher. That means as cumulus clouds absorb heat rising from below and grow, the temperature on top of the cloud drops. If the top of a cloud cools by 6 C (about 10.8° Fahrenheit) or more in the 15 minutes between satellite sensor readings, that means the cloud is growing fast enough to raise the probability that it might soon start producing rain and/or lightning.

The NWS Doppler radar network provides comprehensive coverage of storms that have developed, so SATCAST focuses on clouds before rain starts to fall: Once rain begins that cloud is dropped from SATCAST’s monitoring in favor of the local Doppler radar nets.

UAH's SATCAST system has been in use by the Federal Aviation Administration for more than a year. It was incorporated into FAA weather forecasting software used to plan thousands of airline and commercial airplane flights in the U.S. every day.

More recently, it has become part of the tool kit used by forecasters in National Weather Service local offices across the SATCAST coverage area, as well as the Aviation Weather Center, Mecikalski said.

"There are some weather service offices that really like our product," he said. "They like what they see and they're impressed that it catches even small, local events. If SATCAST detected a new storm that was developing and you had a moderate risk of severe weather, you could put out a warning 30 minutes to an hour earlier than we could before."

In addition to forecasting rain, some NWS offices in the western portions of the SATCAST coverage area have used it to help pinpoint storms that may produce lightning — which can spark forest fires — even when the air is too dry to produce rain.

The SATCAST algorithm is also in routine use in several European countries, including Switzerland, Germany and Hungary. Forecasters in South Africa and Japan are also evaluating components of the SATCAST system.

While SATCAST is part of a robust and extensive network of weather monitoring systems in the U.S., it may have a significant impact in regions where storm forecasting and monitoring systems have been limited or non-existent. The SATCAST system is relatively inexpensive to install and operate, since it uses freely available weather data from existing satellite sensors.

In areas where Doppler radar networks do not exist, SATCAST might be used to track storm systems and provide severe weather warnings that are not now available, Mecikalski said. "This makes SATCAST and satellite-based rainfall predictions very relevant in developing countries, where ground-based radar is absent but high-quality satellite data are in place."

NASA's Short-term Prediction Research and Transition Center on the UAHuntsville campus is helping to train NWS forecasters on SATCAST capabilities.

The UAHuntsville team is also working on a next generation SATCAST, which will take advantage of improved sensing systems on NOAA's GOES-R satellites starting in 2016. Sensors on those satellites will collect data in more channels, more often and at higher resolution.

SATCAST development has been supported by grants from NASA's Applied Sciences Program, the National Oceanic and Atmospheric Administration, and the National Science Foundation.