Positive lightning is particularly dangerous. It originates at the top of a thunderstorm, where cloud tops are positively charged, and can strike as many as 25 miles away from its parent thunderstorm, where the ground is negatively charged.

If you can hear thunder — even from a very distant storm — it’s still possible to be struck by positive lightning.

Negative lightning, on the other hand, originates from the lower-level clouds in a thunderstorm, which are negatively charged, and the bolts often strike directly under the thunderstorm where the ground is positively charged. Negative lightning takes a much shorter path to the ground, compared with positive lightning and often strikes in or near the thunderstorm’s rain shaft.

The term “bolt from the blue” references positive lightning that travels outside a thunderstorm, through clear sky, and strikes the ground many miles away from its origin. It’s particularly unexpected and extremely deadly.

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Because positive lightning must traverse a much greater distance through the air than negative lightning, it tends to be about five times more powerful. It can have more than double the volts and 10 times the amps of negative lightning. The bolts are also hotter and can last 10 times longer than negative lightning.

To avoid the dangers of positive lightning, don’t start or restart outdoor activities when the rain from a thunderstorm ends. It’s best to wait 30 to 45 minutes after the storm passes, and when you can no longer hear thunder.

This positive lightning flash originated over Falls Church, Va., at 27,600 feet above the ground and struck near Silver Spring, Md., spanning a distance of 9.22 miles, on June 25, 2014.  Note the patch of clear sky in the middle-right of the photo. The lightning in this photo was mapped by NOAA’s Scott Rudlosky using data from the Washington D.C. Lightning Mapping Array (DCLMA). (Kevin Ambrose)

Facts about positive lightning:

  • Less than 5 to 10 percent of lightning strikes are positive. The rest are negative.
  • More lightning strike victims are stuck by positive lightning than negative lightning.
  • Positive lightning carries a much greater charge and a longer flash duration than negative lightning, reaching up to 1 billion volts and 300,000 amps, compared with 300 million volts and 30,000 amps with negative lightning.
  • Because positive lightning carries more charge than negative lightning, fatality percentages are higher with positive lightning strikes compared to negative lightning strikes.
  • A significant percentage of forest fires are started by positive lightning strikes.
  • Positive lightning is usually composed of one stroke, while negative lightning often has two or more strokes.
  • Winter storms produce a higher percentage of positive lightning strikes, compared with summer storms.

The lightning safety motto from the National Weather Service is “When thunder roars, go indoors.”

But if there is no building or vehicle nearby, here are some outdoor lightning safety tips from the National Weather Service:

  1. Avoid open fields and the tops of hills.
  2. Stay away from tall, isolated trees or other tall objects. If in a forest, move to an area with lower stands of trees.
  3. Groups of people should spread out to avoid the current from a lightning strike traveling among group members.
  4. If camping, choose valleys or low areas for tents. Remember, tents do not offer lightning protection.
  5. Stay away from water and wet items, including ropes, fences and poles.
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