Cold (winter) air has less water (moisture) in it. So, if you wanted to reduce static in your home, you could use a humidifier in the winter.
Water in the air is what steals away extra electrons that hang out on us, so that's why it matters. To see the effect in real life, and how powerful it is, take a balloon and rub it against your hair or fleece. The rubber on the balloon will steal some electrons from you or the fleece. Now, turn on your water to a slow continuous stream, and hold the balloon next to it. You should see the water bend, trying to get to the balloon.