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Lightning Safety Program
June 20, 2012
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Bolts From the Blue

One of the most dangerous types of cloud-to-ground lightning are bolts from the blue. A "Bolt from the Blue" is a cloud-to-ground lighting flash that typically:

  • Comes out of the back side of the thunderstorm cloud
  • Travels a relatively large distance in clear air away from the storm cloud
  • Then angles down and strikes the ground.

These lightning flashes have been documented to travel more than 25 miles away from the thunderstorm cloud (see the "LDAR" discussion below). Bolt from the Blue lightning flashes are a particularly dangerous type of lightning flash, as they appear to come out of clear sky. This type of lightning is why it is dangerous to be outside when thunderstorms are in the region, even when skies are still clear. Lightning can, and does, strike many miles away from the thunderstorm cloud itself. It is a good idea to wait 30 minutes or more after the rain ends before resuming outdoor activities.

Bolt from Blue going left from clouds by Al Moller
Bolt from Blue going right from clouds by Robert A. Prentice, 1990
Bolt from Blue going straight down from clouds by Robert A. Prentice, 1990

Special thanks to Robert Prentice and Al Moller for allowing me to use their photos.

Bolts from the Blue as seen by lightning detection devices

The image below is a "bolt from the blue" detected by a lightning detection system which observes lightning in 3 dimensions. (This 3D lightning detection system is called "LDAR"; see below). The colored dots represent the lightning channel of a cloud-to-ground lighning flash that struck in east central Florida. Note how this flash travelled to the east 40 KILOMETERS (~25 miles) in less than 1 second, and then struck the ground! (note distance on horizontal axis in upper left box, time is upper right box). This flash struck very close to the National Weather Service office in Melbourne, FL. At the time of the flash, the skies where mostly sunny at Melbourne. The storm was about 35 kilometers to the west of Melbourne (Note: ~1.6 Kilometers = 1 Mile).

See caption above

Below are two other examples of Bolt from the Blue. The first image showed a bolt from the blue which occurred near the Kennedy Space Center, FL. This flash is overlayed on radar data collected near the time of the flash. Note how the flash travels away from the radar reflectivity into clear air. This flash travelled about 6 kilometeres in clear air before hitting the ground. The small white "x" marks the location of where the cloud to ground lightning flash hit the ground. The second flash is similar to the the KSC data, but was collected from a storm which formed in NE Colorado during the STEPS experiment.

See caption above

See caption above

Lightning and radar data for July 11, 2000 for a storm on the Colorado and Kansas border during the STEPS experiment. Image courtesy of Dr Bill Rison of New Mexico Tech and Daniel W. Breed Project Scientist at NCAR's Research Applications Laboratory. Bolts from the Blue are obviously dangerous to the general public as they can strike many miles away from the thunderstorm.


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