There are about 100,000 thunderstorms each year in the U.S. and about 10 percent reach severe levels. Bolts of lightning tear up the air to temperatures about five times hotter than the sun. Yet we rarely have power outages in our homes or businesses considering the intensity and number of thunderstorms.
When an electric outage happens, why? That outage problem is typically a physical versus an electrical reason. Wind, not lightning, is often the culprit. Trees and branches can fall on power lines. Preventing that is a reason utility crews trim back trees near lines. Crews look ahead and prevent problems.
“The outflow of a storm has winds that can easily exceed 70 mph,” says Terry Shirley, Meteorologist and the Meteorology Undergraduate Coordinator at UNC Charlotte. “The rain is added to that, and when we have lots of rain over a long period, like we have in late May this year in parts of the Carolinas, the ground gets saturated, which can allow trees to uproot easier.”
(Photo: Heavy rain from a thunderstorm in Charlotte in early June.)
From a power delivery perspective, system safeguards are often in place. Lightning arresters (also classified as voltage surge arresters) are normally installed on equipment that is historically targets of higher voltage strikes. This includes some pole mounted transformers and other equipment in the system. When a higher voltage surge occurs, the arrester is isolated, and the equipment is re-energized after an inspection to check damage. A strike could damage the transformers up to several spans along the line in either direction.
Storms pack significant energy. “The thing I tell people about their power is that each thunderstorm is like a small nuclear reactor. When you think about the amount of energy that they release it is truly amazing,” Brad Panovich, Meteorologist at Charlotte’s WCNC-TV, told us about thunderstorms. “What I have noticed about our storms here, lots of positive lightning strikes. Never lived anywhere with so many positive strikes that cause house fires. Also, a lot of high shear and low CAPE events, meaning we can get severe storms with not much heat and humidity sometimes.” CAPE is “Convective available potential energy,” the amount of energy a parcel of air would have if lifted a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and indicates of atmospheric instability, useful to predict severe weather.
Panovich also says that wind, versus lightning, is a big issue. “The thing that surprises people is how strong the straight-line winds can be. Everyone thinks tornadoes are what it takes to cause damage when these thunderstorms can easily have winds over 100 mph but over a much larger area.”
(Photo: A late afternoon sun lights up departing thunderstorm clouds after cracking a lot of lightning and drenching south Charlotte. It is rolling east over Union and Anson Counties.)
We asked Terry Shirley what advice he hopes the public really understands about storms. “Know the difference in watches and warnings. There is a lot of confusion about that.” Here’s how the National Severe Storms Laboratory defines those terms:
- A Severe Thunderstorm WATCH is issued by the National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center meteorologists that weather conditions are favorable for severe thunderstorms. A watch can cover parts of a state or several states.
- A Severe Thunderstorm WARNING is issued by your local NOAA National Weather Service Forecast Office meteorologists who watch a designated area 24/7 for severe weather that has been reported by spotters or indicated by radar. Warnings mean there is a serious threat to life and property to those in the path of the storm. Find safe shelter. A warning can cover parts of counties or several counties in the path of danger.
Tree First Aid After a Storm is a neat, short article from the National Arbor Foundation
Tree Care Before and After a Storm is advice from the North Carolina Forest Service
Trees and Storm Safety is from the Southern Group of State Foresters. Here’s an interesting item from the webpage: “Historically, more individuals are injured by chainsaws than by the storm that caused the initial damage.”