What causes heat flashes?

Question

When it is so hot outside, there are flashes of light, kind of looks like lighting, but there are no bolts of light, just the flash, and there is no thunder or storm. Why does it happen, what causes it? Thanks =P

Answer 1

the build-up of static electric charges in the sky form lightning.  Positive charges are attracted to negative charges and vice versa.  When lightning travels from cloud to cloud it is called "heat lightning" here in Florida.  Thunder is rarely heard because of the density of the air prevents the sound from reaching the ground, or the storm  far away (greater than 10 miles).

Answer 2

Heat lightning as it is wrongly called is just lightning from over the horizon.  You can't see it's origin just the flash.