Summer Atmospheric Phenomena:
                          Lightning Behind Clouds ?
                          “Heat Lightning” ?


RE: Lightning Behind Clouds?


Tue, 2 Aug 2005 10:02:19 -0400


"Canali, Eric"


"Glenn Walsh" <>



"Lightning behind clouds":  (perhaps?)
In the summertime, cumulonimbus clouds late in the afternoon can grow 
to phenomenal heights as they deliver their mushrooming column of warm,
moist ground-air high into the frigid heights of the atmosphere. Like
titanic towering castles looming miles high over our ant-hill like
cities and countryside their upper reaches are often still seen
illuminated by the rays of the sun when the countryside below had long
since been carried into post-sunset twilight.
Once it gets completely dark even if the local clouds have not developed much
internal storm activity, the lightning flashes in the tops of neighboring storm-clouds,
even ones just over our horizon 30-50 miles away can be seen reflected on the now
otherwise dark, local cloud-tops above us. Add this to the fact that the humid summer
air disperses and conducts light in all directions more effectively through diffusion
than dry air does and people experience what in semi-scientific folklore is referred to
as "heat lightning".
The folksy assumption is that mysterious subtle flashing in the hazy summer night sky,
a sky that is sometimes even cloudless in your locality, is some kind of special
semi-invisible local lightning, has given birth to many impassioned but spurious explanations
for the hours of silent flashes in our muggy summer night sky.
South Hills Backyard Astronomers
Pittsburgh PA
For more information, or a clarification, send your request to the
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Editor’s Note: This Science question was answered by a very experienced amateur astronomer,
who also works as a part-time Tour Guide at the Allegheny Observatory in Pittsburgh.
Allegheny Observatory provides public tours two nights a week from April through October.
Public tours of Allegheny Observatory [located in Riverview Park, in the Observatory Hill
section of Pittsburgh’s North Side] are free-of-charge, but pre-registration is necessary
by telephoning 412-321-2400.
For many years, Eric G. Canali was Floor Manager for the original Buhl Planetarium and Institute
of Popular Science in Pittsburgh. He also was a long-time member of the Amateur Astronomers'
Association of Pittsburgh and is Founder of the South Hills Backyard Astronomers.
Glenn A. Walsh, Author and Editor of History Web Sites on the Internet:
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