Chazal and Rain Clouds

Question

I was read in Torah Tavlin the following:

"Chazal tell us that the darkest clouds contain the most rain."

Does anyone know where the source for this Chazal is located?

Answer 1

Ta'anis 10a:

דכי אתא רב דימי אמר אמרי במערבא נהור ענני זעירין מוהי חשוך ענני סגיין מוהי

Translation:

As when Rav Dimi came [to Bavel from Israel], he said: "They say in the West [i.e. the Land of Israel], 'Light clouds, little water. Dark clouds, abundant water.'"

This follows a statement that R' Y'hoshua' understands this concept to be implied by the parallel verses II Sh'mu'el 22:12 and T'hillim 18:12.