Responsa sur Samuel 1 12:17

Regarding their protest against petitioning on the grounds that it portends curse—even in their opinion [rain] does not portend curse until the month of Nisan [=early spring] has ended, as the Mishna states (Ta’anit 12b): “If Nisan ended and rains fell, they portend curse.” Moreover, in the source for their words, have they not realized that it is derived from a verse (I Samuel 12:17): “Is it not the wheat harvest today? [I will call out to the Lord, and he will bring thunder and rain, and you will know and see that your wickedness before the Lord, in that you asked for a king, is excessive]”? And so which harvest is set for right now, that would mean that we do not need rain? Moreover, the Talmud states on this [Mishna]: “R. Yose b. Avin said: this only applies if no rain had yet fallen, but if rain had previously fallen, the present rain portends blessing.”