Q. If you are in doubt as to what the weather will be like motzei yom kippur, should you say kidush levanah before Yom Kipur?

A. Remoh (O.H. 426: 2) rules that one should not recite Kidush Levanah prior to the night at the end of Yom Kippur, since at that time one is in a state of happiness. However, Biur Halacha (ibid.) quotes the opinion of the Levush who maintains that on the contrary one should aim to include before Yom Kippur the compliance of as many mitzvos as possible, as they may tip the balance on one’s favor.

Horav Shlomo Miller’s Shlit”a opinion is that if indeed reliable weather forecasts are predicting overcasts skies on the night after Yom Kippur, one should recite before. (See also Mishna Berura 426: 20 quoting the opinion of Hagrah).

Rabbi A. Bartfeld as revised By Horav Shlomo Miller Shlit”a