 It is, on average, the coldest month of the year within most of the Northern Hemisphere (where it is the second month of winter) and the warmest month of the year within most of the Southern Hemisphere (where it is the second month of summer).In the Southern hemisphere, January is the seasonal equivalent of July in the Northern hemisphere and vice versa.January starts on the same day of the week as October in common years and April and July in leap years.