1.   Behind the back-to-backs, a bruised industrial sky blackens, and fills with cooking smells, and rains.

2.   The rumbling becomes louder and is interspersed with flashes of lightning as the sky blackens.

3.   The thunder became louder and the sky blackened.

4.   If a shotgun was fired, the sky would blacken with geese and ducks taking flight.

5.   The result is killer sandstorms in which the sky blackens and the air fills with sand and gravel that hits like bird-shot.

6.   The sky blackened, flames raged down the hill, and winds whipped trees around his home.

7.   Skies blackened throughout the day.