Siman 577

In places where excessive rains muddy the ground and prevent plowing or cause other damage, and certainly as in our countries where excessive rains ruin the grain entirely, and for us excessive rains are much worse than a withholding of rains—they sound the alarm and seek mercy. And if the matter is urgent, such that there is no time to sound the alarm according to the order of fasts of the first three, middle, and final ones and to spread them over Monday, Thursday, and Monday, such as when the damage is immediate, and likewise with other troubles when the matter is urgent and there is no time to perform the order of fasts, and according to this the community would need to fast many consecutive days one after another, and this thing is impossible, for many would become ill from this—therefore they do not decree fasts at all, for the community is unable to fast every day, but rather they sound the alarm every day and in every prayer. And sounding the alarm with the mouth is sufficient and not with a shofar, for since there is no communal fast—there is no shofar. And if the individual Torah scholars wish to fast many consecutive days, and they are not concerned that they will become ill, and even if they do not become ill perhaps they will become weak, and it will not be within their power to engage in work or business and they will need the help of others (see Ta'anit 22b)—they may do as they wish.

And what is the sounding of the mouth? That is, when they say certain selichot and supplications, and reach "Answer us, O Lord, answer us" according to the order of the alphabet according to the known version, they say afterward: May it be Your will, O Lord our God and God of our fathers, that Your mercy may suppress Your anger from us, and Your mercy may prevail over Your attributes, and may You conduct Yourself with Your children with the attribute of mercy, and enter with them within the line of the law. And in Your great goodness have mercy on them, for no calamity comes to the world except for the sake of Israel, and they are Your people and Your inheritance whom You brought out from the land of Egypt. And they are unable to receive neither an abundance of good nor an abundance of evil. You bestowed upon them an abundance of good – they are unable to receive it. You were angry with them – they are unable to receive it. May it be Your will that there be relief in the world, and remember Your mercy. And now the custom is to say this version in "Shomea Tefillah," and no more, when there is an abundance of rain. (And one must be precise regarding the words of the Shulchan Aruch that we brought, that since they cannot decree many fasts upon the community – they do not decree fasts at all. And it is difficult: let us decree at least one fast! Rather, it appears that they do not decree a fast for an abundance of rain. And also among us the custom is not to decree a fast for an abundance of rain. And that which we wrote for the reason that the community is unable to fast every day – this refers to other troubles, and see Magen Avraham. And in truth, there one should decree one fast, and one must deliberate on all this. And be precise and you will find it easy.)