Is the supplication "O Allah, a beneficial downpour" said when snow falls, and then "We have been rained upon by the the grace and mercy of Allah" after it stops? And is the time of its falling a time of answered prayers?

Snow is frozen water that descends from the sky, so it is rain. Therefore, supplications should be answered when it falls, and one should supplicate with what is recited during rain, such as saying: "O Allah, [make it] a beneficial downpour," and "Two [supplications] are not rejected: a supplication made at the time of the call [to prayer] and under the rain."