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Oh, a storm is threatening
My very life today
If I don't get some shelter
Oh yeah, I'm gonna fade away … ("Gimme Shelter," The Rolling Stones)

April 22, 2009: Imagine a monster tornado is ripping through a neighboring county and bearing down on yours.

If you live in north Alabama, your forecasters are well prepared to tell you when to seek shelter.

The National Weather Service there shares a building – the National Space Science and Technology Center – with NASA's Short-term Prediction Research and Transition, or SPoRT, Center. SPoRT puts state-of-the-art NASA satellite data directly into forecasters hands, arming them to recognize weather that threatens your safety.

Right: The National Weather Service's Chris Darden (Science Operations Officer) and Mike Coyne (Meteorologist In Charge) handle communications during severe weather. [Larger image]

"It's not just a matter of them throwing random data sets over the fence to us and hoping we might be able to use them," says Chris Darden from the National Weather Service (NWS). "They work with us to figure out precisely what we need. Then they put that data into a format we can read, actually integrating it with our radar displays. And they train us to understand and interpret the information they give us."

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That tornado plowing through an adjoining county is a prime example. SPoRT gives forecasters several tools to help predict a thunderstorm’s potential for spawning such a beast. One of the best such tools is the North Alabama Lightning Mapping Array -- an 11-sensor network that measures lightning around the area.

Think of how your radio crackles noisily when lightning flashes. That's because lightning produces a lot of radio frequency noise. By zeroing in on an unused frequency, the 11 sensors scattered around on water towers, radio towers, and roof tops, measure a storm's total amount of lightning.

Above: Click on the image to launch a 16 megabyte animation of data from the Lightning Mapping Array. It shows the progress of lightning activity in Franklin County, Alabama, during a severe storm in March 2002. [movie]

"The total lightning data can help forecasters predict whether a storm might generate a tornado," says Rich Blakeslee, NASA atmospheric scientist. "We've found that often intercloud lightning – not cloud-to-ground lightning -- suddenly spikes and then, just as suddenly, diminishes a very few minutes before a tornado forms."

Darden adds, "We add the total real-time lightning data to our radar and wind velocity information to help us make that critical decision whether to send out a warning."

SPoRT and other NSSTC programs also have access to another tool -- a Dual-Polarimetric Doppler Radar -- that actually reveals the shapes of raindrops. Traditional weather radar sends pulses of radiation that oscillate in one direction only--horizontally. Dual polarization radar sends pulses that oscillate in two directions--horizontally and vertically. By combining the reflections from both kinds of pulses, scientists can tell what shape and size a raindrop is.

"Flatter and wider means bigger raindrops, because the larger the raindrop is the flatter it gets as it falls," explains Walt Petersen, NASA physical scientist. "That information helps weather forecasters better estimate rainfall amounts – and therefore flash flooding – and storm intensity."

This radar can also tell the difference between rain and hail because hail is typically spherical while raindrops tend to flatten. Adding this information to the strength of the return, forecasters can tell the size of the hail.

Right: A slice through a 2.5 inch hail stone collected at the home of NASA scientist Walt Petersen in Madison, Alabama. "The layering in the stone illustrates the different growth regimes that the hail stone went through (sometimes coated with water, sometimes dry) as it ascended and descended through the storm. We can detect these types of changes on the hailstone surface with the dual-polarization radar." [Larger image]

"Large hail indicates powerful updraft and downdraft winds within a thunderstorm," says Petersen. "So it usually means a strong storm, and sometimes means that a storm may produce a tornado."

"This radar tells us a lot about a potentially violent storm," says Darden. "It's pretty new, so we still have a lot to learn."

No problem. The scientists at the NSSTC train current forecasters and future meteorologists alike to use these cutting-edge tools. University of Alabama Huntsville's Atmospheric Science Department is, like the NWS, collocated with NASA researchers at NSSTC.

"During severe weather, day or night, my students gather here to operate the radar," says Petersen. "You should see 'em. It's like weather central here sometimes!

"When there's a fierce storm brewing, or even crashing around us, the students, UAH and NASA researchers, and forecasters communicate in real time by instant messaging with the NWS's IEM online chat tool (NWSChat). They chat about operating the radar and interpreting the radar data. It's a great hands-on way to learn."

Right: Ph.D. student Christopher Schultz operates the dual polarization radar from his workstation at UAH. [Larger image]

WHNT-TV, a local TV station, also uses the data from this radar, and is in fact the first broadcast meteorology station in the world to have access to such a tool.

"So the benefit goes straight to the consumer--the viewing audience," says Petersen.

And the benefits are not just local.

"We've transferred many of these tools to other forecast offices across the country," says Darden. "For example, our office is one of only a few U.S. NWS offices with access to this kind of radar, but all the offices must convert their radars to dual pole by the end of next year. We'll be helping to train them in its use, passing along what we've learned from SPoRT."

Both the lightning mapping and dual pole radar are ground-based now, but in the future will be space-based.

"We're developing products to work with the Geostationary Lightning Mapper on GOES-R – NOAA's next-generation weather satellite," says Jedlovec. "With the launch of that satellite in about 2015, lightning could be mapped all across the U.S. from the vantage point of space."

Again, thanks to NASA, the NWS forecasters here will be a step ahead in using a new tool, and ready to help other forecasters learn the ropes to help their communities.

"This is an exciting place to work," says Jedlovec. "All the tornado warnings for Madison County come right out of this building. We don't just write research papers. With the help of the National Weather Service, we see our data used for the good of the public. That makes us feel good about what we do."

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Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA