There are several things to consider before telling your family you are an atheist. In my situation, my mom just kind of stopped trying to force me to go to church after I had first communion. I have not actually told her I don't believe in God. I live in a region of the United States where people are "Christian" because their parents are Christian. They "believe in God" but not enough to get out of bed and go to church on Sunday.

In your situation if you tell your family you are an atheist they might get scared and force you to attend synagogue every week because they think they can still change your mind. If I told my mom I am an atheist, I have no doubt she would start trying to get me to go to church again. Try to find an excuse to stay home from synagogue without telling them you don't believe in God.

Also, if you tell them you are an atheist and damage your relationship with your family, they might not help you when you turn 18 and begin to transition into adulthood. If you get kicked out of the house for being an atheist, that could make it much harder to attend college and secure a middle class lifestyle later in life if you have to support yourself economically during college.