The Laws of Mentioning The Wind And Rain And Dew. Containing 9 Se'ifim
We start saying "He makes the wind blow and rain fall" in the second blessing [of the Amidah] during the Mussaf prayer of the last day of Yom Tov of the Holiday [of Sukkot] (ie. Shemini Atzeret), and we do not stop [saying it] until the Mussaf prayer of the first day of Pesach.
It is forbidden to mention rain until the prayer leader announces it. (And some say that before they start the Mussaf prayer, the attendant announces "He makes the wind blow etc.", so that the congregation should remember [to say it] in their prayer, and that is the custom (Mordechi in the beginning of the first chapter of Tractate Taanit)) Therefore, even if one is sick or has an extenuating circumstance [that prevents him from praying in the synagogue], he should not say his [Amidah] prayer before the congregation's [Amidah] prayer since it is forbidden to mention [rain] until the prayer leader does. But if he knows that the prayer leader announced it, even though he [himself] did not hear it, he may mention it. And for this reason, if one came [late] to synagogue and the congregation had [already] started to pray, he should pray and mention [rain], even though he did not hear [the announcement] from the prayer leader.
If one said "He makes the wind blow etc." [in the summer time] or if he did not say it in the winter time, he does not repeat it. And similarly [regarding saying] "dew", if he said it in the winter time or if he did not say it in the summer time, he does not repeat it. Rem"a: And we Ashkenazim do not mention "dew", not in the summer time and not in the winter time; rather, in the summer time we just say "the Powerful One to deliver us. Sustainer of the living" (ie. we do not mention dew in between those) [Tur]. There are those who say that the prayer leader stops mentioning [rain] in the Mussaf prayer on the first day of Yom Tov of Pesach, but the congregation does mention it [in Mussaf]; and they do not stop until Mincha, for by then they already heard the prayer leader stop mentioning it in [the repetition of] the Mussaf prayer. And that is our custom.
If one said "Who makes rain fall" in the summer time, he must pray again; and he goes back to the beginning of the blessing (ie. "Ata Gibor" - the second blessing of the Amidah). And if he concluded the blessing, he must go back to the beginning of the [Amidah] prayer. And even if he is in a place where rain is needed in the summer time, if he mentioned rain instead of dew, he must go back. [And similarly, if he mentioned rain and dew, he must go back] [Beit Yosef in the name of the Rambam, the Ro"sh, and the Tur]
In the winter time, if one did not say "Who makes rain fall", he must go back. And this is if he did not mention "dew" [as well], but if he mentioned "dew" then he does not go back.
In what circumstance are we referring to [when we say] that he must go back when he did say "Who makes rain fall" in the winter time? It's when he concluded the entire blessing (ie. the blessing of "Mechayei hameitim" - "Who revives the dead") and began the next blessing (ie. "Ata Kadosh" - "You are Holy"), then he must go back to the beginning of the [Amidah] prayer. But if he remembered before he concluded the blessing, he mentions it right where he remembered. And even if he did conclude the blessing but he remembered before he began [the blessing of] "Ata Kadosh", he does need to go back, rather he should say "He makes the wind blow and the rain fall" [right there], without [the need to] "seal it" [with a blessing]. Rem"a: The first three blessings [of the Amidah] are considered as one [long blessing], and any place where one made a mistake within them, he must return to the beginning [of the Amidah], whether he is by himself or he is with the congregation [Tur].
Any time we say that one must go back to the blessing that he a made a mistake in, that's referring to when he made a mistake by accident, but if was on purpose and with intent, then he must go back to the beginning [of the Amidah].
In the summer time, if one was in doubt if he [mistakenly] mentioned "Who makes rain fall" or not - up until 30 days, it is presumed that he mentioned the rain and and he is required to go back [and pray again]. Rem"a: And the same applies to us who do not mention "dew" in the summer time; if one is in doubt whether he said "Who makes rain fall" in the winter time - within 30 days, he must go back, for it's certain that he said what he is accustomed to say, and behold he did not mention "dew" nor "rain". [But] after 30 days he does not go back. [His own opinion]
If, on the first day of Pesach, one recited the [words of the] blessing of "Ata Gibor" ("You are mighty") until [and including the words] "Morid Ha'tal" ("Who causes dew to descend") 90 times corresponding to the 30 days where he would say it 3 times in each day - from then on, if he doesn't remember if he mentioned rain, it is presumed that he did not mention rain and he does not need to go back [and pray again]. Rem"a: And similarly for us, if he recited [90 times] up until [and including the words] "Mechalkel chaim" ("Sustainer of the living") without [saying] "Mashiv ha'ruach u'morid ha'geshem" ("He makes the wind blow and rain fall") which we say in the winter time, or if on Shmini Atzeret he said, 90 times, "Ata Gibor" until [and including] "Morid hageshem" - if he was in doubt afterwards if he mentioned it or not, it is presumed that he did mention it. [His own opinion]