A sudden surge in lightning activity along with wild fluctuations in a storm’s electric field may help predict tornado formation a local researcher has found.
A serendipitous encounter with a tornado near Greenbelt, Md. on June 1 this year led to this finding says Johns Hopkins University geophysicist Benjamin Barnum, who presented this work at this week’s annual American Geophysical Union fall meeting.
Strong to severe storms along a cold front were moving through the area that evening, and a tornado eventually formed roughly 10 miles away from Barnum’s location.
At the time, Barnum just happened to be running normal tests at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in Laurel, Md.
JHU/APL operates several single point lightning monitors that measure different aspects of a storm’s electrical life.
These instruments were able to detect extremely high peak rates of lightning just 17 minutes before a tornado was spotted near Greenbelt on June 1.
(In addition to their own sensors, Barnum and his team are also analyzing data from the National Lightning Detection Network, the U.S. Precision Lightning Network, the World Wide Lightning Location Network and the D.C. Lightning Mapping Array (DCLMA), a local network of 10 sensors.)
During the storm’s lightning peak, JHU/APL sensors measured total lightning strikes exceeding 1,000 per minute.
Barnum told me this was atypical and that, “the rapid increase in lightning rates measured by the single point systems ... were nearly double or triple what we usually measured during other thunderstorms during this spring.”
He also notes, “the lightning activity/rates decreased rapidly after 7 p.m., and the tornado was spotted at Greenbelt at 7:06 p.m.”
There is certainly precedent for lightning to ramp up before severe weather. A number of studies in the past have shown at least some correlation between lightning and severe storms.
Another recent example case occurred on March 2, 2012. Forecasters at NWS Huntsville, Alabama noticed an increase in lightning on a developing storm. This fact helped push them to issue a warning. In the 20 minutes thereafter, severe weather reports trickled in, including a confirmed tornado.
However, many scientists heavily involved in lightning and severe weather research point out that a “lightning jump” (quick and intense increase of lightning) cannot discern severe weather types. Rather, lightning jump can indicate the updraft (and hence the storm itself) is strengthening.
In essence, this technique of lightning data monitoring can help to “tip the scale” on whether or not to issue a severe warning.
What made the June 1 D.C. area event unique, from Barnum’s point of view, is that there were extraordinarily quick changes in the electrical field of the storm, something he refers to as “rapid oscillations in the vertical fields.”
“The electric field oscillations were quite different from the types of electric field changes we measure from regular lightning strikes,” Barnum said.
The fluctuations end as the tornado develops.
Barnum is quick to admit that these phenomena are not always observed with such events. He also points out this is the first time he has measured a tornado so close to the JHU/APL sensors.
Zac Flamig, a Ph.D student in meteorology at the University of Oklahoma, who guided me to some of the better literature on the larger subject, is also understandably cautious.
Flamig says that from what he has seen in his research, he does not “believe increased lightning activity can differentiate a storm strengthening non-tornadically vs. one strengthening tornadically.”
He reminds us, “there are cases where severe weather occurred with a complete lack of lightning.” Still, Flamig points out that a better understanding of lightning’s relationship to the larger storm will provide a more complete picture for operational meteorologists.
Regardless of any qualifications, Barnum’s findings appear ripe to feed more data into the research of lightning and its potential signal for tornadic activity. As anyone in the field will tell you, the more early warning of any severe weather, the better.