Rabbi David Lau, Israel's Ashkenazic Chief Rabbi, was asked recently whether it is appropriate to pray for rain when precipitation may negatively affect Israel's war with Gaza.
The question, which came from religious IDF soldiers, referred to a request to "grant dew and rain for blessing," said during the winter months in the Amida prayer. In Israel, this request is added beginning about two weeks after the Sukkot (Feast of Tabernacles) holiday, on the seventh of the Jewish month of Heshvan. In the Diaspora, the request is added to the Amida prayer on December 4 or 5, depending on the year.
In his response, Rabbi Lau ruled that the request should be said as usual, and explained two reasons for his opinion: Firstly, "at this stage it seems that the fighting will continue for an extended period of time, and it does not seem correct to cancel the request for rains for a lengthy period of time."
Furthermore, Rabbi Lau explained, "We are requesting in this prayer for rain, 'Grant dew and rain - for blessing.' Thus, we are asking G-d to give us rainfall that will be for a blessing, and that will not, G-d forbid, cause a mishap or disturb Israeli soldiers during the fighting."
The Chief Rabbi concluded his letter with a prayer for the welfare of the soldiers, asking that G-d "protect them from any trouble or distress, watch over them, and bring them home healthy and whole."