A Flash of Lightning

North Carolina is one of the most dangerous states for the number of lightning fatalities, but new research makes nature’s light show more predictable.

RALEIGH — The everyday weather we all live in is a little like politics and real estate—what’s happening locally really matters.

“What happens where you live is really important,” says Jonathan Blaes, Science Operations Officer with the National Weather Service in Raleigh. “Most of us in North Carolina and the southeast United States are familiar with summer storms, where it may rain and thunder in your neighborhood and if you drive a few miles away you find that nothing has happened.”

As another example of how local weather matters, Blaes adds that the same phenomenon happens in the winter; heavy snow in one area of a county but nothing in another part. 

It’s even more important when talking about lightning, because North Carolina has ranked sixth in the nation for the number of lightning fatalities over the past 15 years—for a number of reasons.

“That’s largely a result of the number of storms we get, but it’s also because of lifestyle and sociological issues,” explains Blaes. “In the summer when storms are at their peak, there are lots of people at the beach, playing golf, working outside on the farm or just spending time outdoors. It’s something we take very seriously,” which is why Gary Lackmann of NC State University’s Department of Marine, Earth and Atmospheric Sciences is working with the National Weather Service to improve the understanding and forecasting of lightning.

“Typically the summer air mass here is hot, humid, and unstable, and along the coast we have a sea breeze that helps to lift the air and release the instability,” explains Lackmann, who adds that all of the ingredients for thunderstorms with lightening are present in a North Carolina summer. “We have the fuel and we have the spark.”

So just what is the fuel and spark for a lightning-filled storm?

First, you need ice. That’s right, ice.

That means a cloud that is sufficiently tall enough to reach colder temperatures where ice will form and stay solidified.

All those ice particles swirling around in the cloud bang into each other, causing a separation of charged particles. Positively charged particles rise to the top of the thunderstorm. Negatively charged particles and hailstones drop to the bottom of the cloud.

As the charge grows, the negatively charged bottom of the cloud sends out an invisible charge towards the ground. As the charge gets close to the ground, positively charged objects on the ground attract it, and a channel develops. The electrical transfer in the channel is lightning.

But lightning isn’t limited to a flash that extends from a cloud to the ground. Lightning comes in different forms, including positive and negative discharge, cloud to cloud, within cloud, cloud to air and cloud to ground.

Lightning-related fatalities have dropped, thanks to technology showing the current location of storms. Meteorologists can also now predict the odds of a storm forming in a given area. That’s why storm predictions always include a percentage chance. For example, a forecast will list a 60% chance of rain. The goal for weather researchers is precision forecasting; that is, predicting when and where a storm will hit.

“We can predict the environment of the storm because we have computer models that have all of the equations that govern the motions of the atmosphere and we can project them forward in time to what the weather maps will look like,” says Lackmann. “What we can’t say yet is there will be a storm over Chapel Hill at 3PM.”

But the work is progressing. 

Dianna Francisco, who is working on her Ph.D in Atmospheric Science, is testing lightning forecast models against days in which a large number of lightning strikes were reported. That includes central North Carolina, on July 28, 2005, when there were 39,754 cloud to ground lightning strikes in a 24-hour period. It is the worst day ever for lightning strikes in the state.

“These computer models can generate clouds, which turn into thunderstorms,” says Francisco. “Since we know the ingredients of lightning, we can predict the general area where lightning strikes will be and even estimate the number of strikes in the area. There is still a lot of work to do but we’re getting close.”

Researchers are starting to blend computer models with radar images of storms to give a short-term forecast of where lightning will be in a couple hours. Lackmann is confident better lightning forecasts will be coming.

“I think you will see in next five to 10 years the ability to say if you have a football game at the stadium with a 1PM kickoff, you may want to delay the start of the game because there will lightning in the area.”

Related Resources: