la"n ZVI YEHUDAH BEN MOISHE- NIFTAR LAMED KISLEV ALEF D'ROSH CHODESH TEVES

A few years ago the two brothers, Menachem and Mordechai lost their mother Miriam. They both live presently in the same city and both daven and learn in the same shul. Their Rov paskend that Menachem has Yahrzeit (after the same mother) one day before Mordechai 


The year Miriam died , had two days Rosh Chodesh. She died on the first day Rosh Chodesh Teves (30 Kislev) The following year ( first yahrzeit) It was only one day Rosh Chodesh (there is no 30th kislev) In this case there is a machlokes haposkim* which day to keep the yahrzeit

 HALACHA V'LO LEMA'ASEH 
 The Mogen Avraham (#568) holds you keep the yahrzeit on the 29th of kislev which corresponds with the last day of the month, and since you started the first yahrzeit on the 29th, you continue for the rest of your life on the 29th of kislev. The Shaarei Teshuva ,Bigdei yesha and Aruch Hashulchan, hold you always keep the Yahrzeit on Rosh Chodesh. The first year after Miriam’s death ,Menachem davened in BHM”D Chofetz Chaim. He asked his Rov when to keep the yarzeit . His rov said, The mishna Veruro who is considered the posek achron, writes (568 sk 42) that the minhag is like the Mogen Avraham. Therefore being this year there is only one day Rosh Chodesh, he has to keep the yahrzeit on the 29th of Kislev. He must also continue to do so all the years, the Magen Avraham writes the first yahrzeit establishes all the coming yahrzeits. Mordechai davened in Tiferes Yerushalayim and asked his Rov when to keep the Yahrzeit. His Rov answered that R. Moishe was the poisek hador in America. In Igros Moshe (Y.D. 3-159) he disagrees with the Magen Avraham and paskens like the Aruch Hashulchan etc. therefore he should keep the Yahrzeit on Rosh Chodesh Teves. By the time the second yahrzeit came around Mordechai and Menachem ended up davening in the same shul and asked the sheilo from their new rov. The rov paskened, Menachem started his first yahrzeit on the 29th of kislev He must continue the 29th. Mordechai started the first yahrzeit on Rosh Chodesh , he must continue on Rosh Chodesh. (no one disagrees with the magen avraham, that the first yahrzeit establishes the date forever.) * There are two more shitos 1) Taz 2) Elef Lamateh