The moon does have an effect on Earth's weather, but apparently no one knows for certain how. The moon causes atmosphere tides, just as the moon causes oceanic tides. It appears that you can expect colder temperatures when the moon is full or new due to this effect. When the moon is full or new, it causes a bulge in the atmosphere, just as it causes a bulge in the Earth's oceans. When the moon is full or new, the Earth, Moon and Sun all line up, and the gravitational forces of the Sun and Moon act together on the Earth. This effect is especially pronounced when the moon is closest to Earth (at perigee). When the moon is at perigee and when the moon is either full or new, a particularly pronounced drop in temperature can be expected. Right now, the moon is full and at perigee; it is also January, the coldest month of the year. Here in Minnesota, the temperature last night was 28 below 0, Fahrenheit, which is unusually cold, even for Minnesota. While this effect may be noticeable, most meteorologists agree that other atmospheric factors play a greater role in Earth's weather patterns.