In Eretz Yisroel they begin to say “vesen tal umatar” on zayin Cheshvan. In Chutz Le’Aaretz we begin saying “vesen tal umatar” on December 4th or on December 5th the year before a secular leap year. In the event that a person from abroad is in Eretz Yisroel on the 7th of Cheshvan we find that there is a machlokes haposkim whether the person should say vesen tal umatar or not.  

The Chazon Ish and Tchebiner Rov paskened that the people of Chutz LeAaretz should say vesen tal umatar in their davening just like the inhabitants of the place where he is at that moment, which is in Eretz Yisroel. This is their psak even in a case where the person will go back home before the month of Nissan

In the event that a person arrives in Eretz Yisroel after zayin Cheshvan but will be returning home before December 4th, the Birkei Yosef 117:6  paskens that once he begins saying vesen tal umatar he continues saying it even upon returning to Chutz Le’Aaretz where they did not yet begin to say vesen tal umatar. In the Teshuvos of Chaim Shnayim Yeshalem it would seem that one should not continue saying vesen tal umatar upon returning to Chutz Le’Aaretz

There is a way for a person to be yotzei both shittos. The person should say vesen tal umatar during the bracha of Shomea Tefilla. He covers all scenarios this way since if he is required to say vesen tal umatar then he is yotzei by saying it in the bracha of Shomea Tefilla, and if he is not required to say vesen tal umatar then it would not be a siman klala by saying it in Shomea Tefilla as it would be in saying it in the bracha of Bareich Aleinu

The only question that arises is what should someone say if he is a shaliach tzibbur? The rule is that a shaliach tzibbur can’t say anything that has no connection to the tzibbur and since the tzibbur does not need to say vesen tal umatar he can’t say it in the bracha of Shomea Tefilla. He can’t say it even if he will say it quietly. 

We find a similar question arise when a person is davening on Shabbos and by mistake starts Ata Chonen, which is the weekday tefilla. He should complete the bracha and then continue with the Shabbos davening. In the event that this happens with the shaliach tzibbur, we don’t say that he should complete the bracha since the tzibbur is not required to say a weekday Shmone Esrei

This would render a person who went to Eretz Yisroel and came back before they started vesen tal umatar not eligible to be the shaliach tzibbur. He still could daven to himself and not say vesen tal umatar in Bareich Aleinu, but rather say it in Shomea Tefilla hereby following both opinions. 

May we all be zocheh to live in Eretz Yisrael and not have these questions anymore.