Climatologically, the end of January is the coldest time of year. The reason for this lag is due to the continued low sun angles, short days and snow cover. The areal extent of snow cover in North America often reaches it maximum in January. Snow cover can cover most of North America, except for the deep south and far west by the end of January. This is an important factor in keeping the land very cold.
Snow cover reflects a large amount of sunlight back into space.
This, combined with low sun angles, does not allow the sun to heat the land very much, even with the lengthening amount of daylight that occurs in January. This is the main reason why it continues to get colder in January. At our latitude, it takes until February for the sun to begin to heat the land significantly to overcome the cold of winter. Normal high temperatures in January range from the mid 20s to lower 30s in most parts of central New York and northeast Pennsylvania. Normal low temperatures range mainly in the teens.