Now Deborah, a prophetess, the wife of Lappidoth, she judged Israel at that time.
"The river Kishon"  (Judges 4:7).  In normal weather this river is merely a dried up wady, but in the instance of a rain, it becomes a roaring river.  Of course, Sisera knew that, and, if it had been the rainy season, he would not have deployed his chariots in such a dangerous location.  This indicates that it was certainly an unexpected and untimely rain that turned the battle into the advantage of the Israelites.  It was through her gift of prophecy that Deborah knew this and set in motion the events that led to the great victory.