Why January is the coldest month?

Answer 1

The shortest time of the year is the winter solstice, which happens at the end of December, the place of earth where you live is receiving the least amount of solar radiation (heat). With the decreasing solar radiation heating your area, it takes more and more to increase the temperature. So it's a delayed effect, the mean temperature keeps dropping with the increasing solar radiation not enough to overcome the falling temperature. So it takes longer for the temperatures to start rising.

Of course cold fronts from different areas of the world can drastically affect that as well.

Answer 2

January is typically the coldest month in many regions because it follows the winter solstice, when the Earth's northern hemisphere is tilted furthest away from the sun. This results in less direct sunlight and shorter days, leading to colder temperatures. Additionally, the accumulated cold from the preceding months tends to peak in January.