Boulder experiences four distinct seasons, and you will need clothing for all four. Winters can be very cold and snowy; heavy coats, boots, hats, and gloves are necessities. Young children keep warm in snow pants, winter jackets, mittens, and hats.
That being said, Boulder also enjoys an average of 300 days of sunshine annually, so snowfall often melts quickly. Warm, layered clothing is a good idea during the transitions into and out of winter.