On the day the devastating tornado hit Moore, Okla., Robert Marshall sat glued to the news, watching images of the deadly twister on CNN while he also monitored it on his computer.
Marshall, the energetic CEO of Earth Networks, a company that owns and operates an enormous network of weather sensors, was looking for one thing in particular: lightning. But he didn't see it.
"These tornadoes from a couple weeks ago were probably the most videotaped tornadoes in history. If you just watched the video, there's almost no lightning," Marshall said.
Visible lightning, that is. In fact, as Marshall explained, there actually was lightning, a whole lot of it, in the storm that caused the Moore tornado. It's just that most of it didn't hit the ground and was thus unseen by humans.
Earth Network's "Total Lightning Network" saw it, though. That's because this network, which consists of about 600 stations across the United States, has instruments that can track in-cloud lightning, the flashes that occur within a cloud and never make it to the ground.
Storms can have a lot of this type of lightning, and researchers have been working hard to understand how surges in it are related to severe weather events like tornadoes. What they are learning holds considerable promise to improve weather forecasters' ability to issue severe weather and tornado warnings earlier and more accurately.
"It's really clear that lightning data is very helpful for both our models and our forecasters," said Alexander MacDonald, director of the National Oceanic and Atmospheric Administration's Earth System Research Laboratory in Boulder, Colo.
Meteorologists still don't understand exactly how lightning relates to severe weather, but they know there is a strong correlation.
Telltale signs of growing strength
As a storm builds and more ice particles collide in a cloud, the rate of lightning flashes increases. This increase is often tied to a future growth in a storm's intensity.
Eric Bruning, an assistant professor of atmospheric science at Texas Tech University, said the flashes of in-cloud lightning might be few and far between as a storm gets organized, but as it gathers energy and moisture, that can change quickly.
"As it really taps into that deep moisture source, that flash rate will go up substantially, and it's a really sensitive indicator of that storm becoming more established," Bruning said.
Lightning researchers call this a "jump." In the Moore tornado, Marshall watched it happen on the Earth Networks' lightning network in real time.
"That Moore tornado ... that particular tornado went from no lightning and really no storm to like 50 flashes per minute," Marshall said. "It's a very classic scenario where you have a significant rise in lightning well in advance of the tornado."
On May 20, when the tornado hit Moore, his network saw its first spike in lightning to around 33 flashes per minute at 2:13 p.m., which is when it would issue a warning.
At 2:35, the in-cloud lightning hit 50 flashes per minute. The tornado touched down in Newcastle, Okla., at 2:56.
Not all jumps mean the storm is going to strengthen or a tornado is going to form. Figuring out that relationship between a jump and the severe weather that can follow is what Chris Schultz, a NASA scientist and a doctoral student at the University of Alabama, Huntsville, is working to figure out.
Schultz's doctoral work focused on developing an algorithm that relates lightning jumps to severe weather.
If he can do this -- and his formula is currently being tested at NOAA's Hazardous Weather Testbed in Norman, Okla. -- he could help forecasters improve their lead time on tornado warnings.