Q. When someone makes Kiddush Levana on a winter, cloudy and windy day, how long does the moon have to remain uncovered to be able to recite the Bracha? What can be done when it is extremely cold and likely, at least some of the present will not make Kiddush Levana later, can they do the Bracha when they only see the moon a short while?
A. Mishna Berura (426: 3) rules that if one began reciting the brocho while the moon could be seen and then it became covered, he may finish the brocho. However he adds (quoting from Ridbaz and Magen Avrohom), that if he expects that the clouds will cover the moon before he can end the brocho, he should not begin to recite.
Nevertheless, in Biur Halocho he quotes Divrei Chaim that one may start immediately to recite the blessing even if he knows it is going to be covered before the end of his blessing. He compares the above to the brocho on lighting.
Biur Halocho suggests that there is a slight difference between the brocho on lighting, that is recited to recognize the portents and prodigies of Creation and that is immediate, as opposed to Kiddush Levana, in which we bless Hashem for the enjoyment of the light of the moon, and that may take longer.
Horav Shlomo Miller’s Shlit’a opinion us that in case of need one may rely on the Divrei Chaim and other Poskim that permit.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller, Horav Dovid Pam and Horav Aharon Miller Shlit’a