Answer: Clouds that are deep enough to produce heavy rain, lightning ... appear dark due to the lack of light passing though it, and likewise it will become rather dark underneath the storm.

A tornado warning was issued in several counties, and storms filled the sky with lightning and dark cloud formations ... sent in footage and photos of storm activity that took place.

Dark storm clouds loomed over San Antonio, Texas, as a dramatic lightning storm swept through the city on May 24. A tornado warning was in effect for Bexar County and a severe thunderstorm watch in ...

A strong and slow-moving storm system may flood our streets, creeks, streams and rivers, according to KPRC 2 meteorologist Anthony Yanez.

It's possible the positron clouds are a sign of a theoretical phenomenon called dark lightning, whereby high-energy particles are accelerated, producing positrons and helping discharge storm clouds.