Midrasz do Joela 2:23

(Fol. 5) MISHNAH: Till what time should the petition for rain be recited [in the ninth Benediction]? R. Juda says, "Until after the Passover." R. Jose says, "Till the month of Nissan is over; because it is said (Joel 2, 23) And he hath caused to come down for you the rain, the first rain, and the latter rain the first month."

The yoreh falls in Marcheshvan; the malkosh in Nissan. You say: The yoreh in Marcheshvan and the malkosh in Nissan. — But perhaps, the yoreh in Tishrei and the malkosh in Iyyar? It is, therefore, written "in its (proper) time" — the yoreh in Marcheshvan and the malkosh in Nissan. And thus is it written (Ezekiel) 34:26) "And I shall bring down the shower in its time; (showers of blessing shall they be.") But perhaps (it is called) "yoreh" (to shoot) in that it makes the fruits fall and floods the seeds and the silos! It is, therefore, written "and malkosh." Just as malkosh is for blessing, so, yoreh. — But perhaps, just as malkosh topples houses and uproots trees, and brings the cricket! It is, therefore, written "yoreh and malkosh." Just as yoreh is for blessing, so, malkosh, viz. (Yoel 2:23) "And, sons of Zion, be glad and rejoice in the L-rd your G-d. For He has given you the moreh in righteousness, and He has brought down for you rain — moreh and malkosh in the first (month)."