Get a heads up on pop-up storms before there’s rain to see on radar
HUNTSVILLE, Ala. (Sept. 12, 2012) — A tool developed at The University of Alabama in Huntsville (UAHuntsville) is helping people who work or play outdoors across the U.S. get an advance warning of pop-up summer storms before they pop up on radar.
Using data from the GOES–East and –West geostationary satellites, the UAHuntsville program can predict which puffy summer clouds are most likely to produce rain and lightning in the next 15 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 might be interested in using this resource,” said John Mecikalski, the SATCAST (Satellite Convection Analysis and Tracking system) project director and an Associate Professor in the Atmospheric Science Department at UAH. “It might be useful, for instance, to people in the construction industry, or farmers thinking about spreading chemicals on their fields, or 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 rain might start in the near future have not been notoriously accurate in forecasting either the when or the where.
SATCAST 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 seven-year development, UAHuntsville scientists learned that important factors in predicting thunderstorm formation are temperature change in the tops of clouds, 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 transfer heat rising from below and grow, the temperature on top of the cloud drops. If the top of a cloud cools by 4 C (about 7.2° 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. Other fields provided by GOES also help determine if the cloud’s top is turning to ice, and how tall the cloud extends in the vertical direction. Tall, rapidly growing clouds with a lot of ice at cloud top are those most likely to form rainfall and lightning within 30 minute to 2 hour timeframes.
UAHuntsville’s SATCAST system has been in use by the Federal Aviation Administration (FAA) for about a year. It was incorporated into FAA weather forecasting software used to help plan and guide 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 (NWS) local offices across the SATCAST coverage area, 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, especially in locations where radar observations are limited and where mountains block radar coverage. If SATCAST detected a new storm that was developing in a situation when a moderate risk of severe weather existed, one could put out a warning 10-30 minutes earlier than we could before.” In addition to forecasting rain, some NWS Forecast Offices in the Western U.S. have used SATCAST to help pinpoint storms that may produce lightning — which can spark forest fires — even when the air is too dry to produce rain. This information can then be passed along to Forest Service offices who can respond to actual wildfires.
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 the likelihood of precipitation from that cloud goes to 100 percent and it is dropped from SATCAST in favor of the local Doppler radar tracking.
The SATCAST algorithms are also being studied by forecasters in Europe, South Africa and Japan, and has been implemented in several nowcasting systems. Weather service offices and developers of convective weather forecasts algorithms in Europe are particularly interested in SATCAST, with an evaluation planned between several forecasts offices (from several countries) in summer 2013.
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 forthcoming GOES-R satellites starting in 2016. Sensors on those satellites will collect data in more channels, more often and at higher spatial and temporal resolutions.
SATCAST development has been supported by grants from NASA’s Applied Sciences Program, the National Oceanic and Atmospheric Administration, and the National Science Foundation.
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