This Halacha is an excerpt from our Sefer
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In Nussach Sefarad and Arizal, in Musaf of the first day of Pesach one stops reciting Mashiv Haruach Umorid Hageshem and rather recites Morid Hatal. The Gabbai is to announce prior to the silent Shemoneh Esrei of Musaf that Morid Hatal is to be said.
If one accidently said Mashiv Haruach Umorid Hageshem: If one accidently said Mashiv Haruach Umorid Hageshem and then remembered prior to concluding the blessing, he is to return to the beginning of Ata Gibur. [If he already completed the blessing, then by Musaf of the first day of Pesach he is to continue as usual. However, from Mincha and onwards, he is required to repeat from the beginning of Shemoneh Esrei.]
What is one to do if he has not yet Davened Shacharis and the congregation has already Davened Musaf?
Once one’s affiliated congregation has prayed Musaf, and thereby began omitting Mashiv Haruach, then one who is praying in private and has not yet davened Shacharis, is to omit it from his Shacharis Shemoneh Esrei.
 Admur 488:7
Background: In Nussach Ashkenaz, in which the custom is not to say Morid Hatal in the summer months, by the silent prayer of Musaf, Mashiv Haruach is said as usual, while in the Chazan’s repetition, Mashiv Haruach is omitted. In Mincha, everyone omits it. In Nussach Sefarad and Ari, in which the custom is to say Morid Hatal in the summer months, the Gabbai announces prior to the silent Shemoneh Esrei that Morid Hatal is to be said, and one begins saying it from that Musaf.
 Admur 114:4
 See Kaf Hachaim 114:24
 Admur ibid
 Shevach Hamoadim based on an edited portion of Kolel Chabad; See Sefer Haminhagim p. 69