It’s December—time for the longest night of the year. With so little warming sunlight, it will be the coldest day of the year. Right?
It depends where live! California, your coldest days are in December! Massachusetts, your coldest days are in January!
See the map below showing when coldest weather usually hits different parts of the USA. Notice a pattern?
Winter cold sneaks up on the West right away.
It usually waits until January to hit most of the East.
Up around the Great Lakes, the coldest weather may wait a while and hit them in February.
It’s confusing but the explanations are actually as simple as snow and water.
Still cooling in late January. Blame the snow! Source: Sara2 at Wikipedia
Some areas in the West—the Rocky Mountains and California’s Sierra Nevada Mountains—cool off slower than the low-lying Western lands.
In the low-lying lands, the less Sun, the colder it gets, so most of these areas celebrate the winter solstice by being cold. As the days get longer, they warm up.
But the mountains, as every skier knows, are covered by lovely snow. The snow reflects back the sun, keeping it from warming things up. So snowy areas keep getting colder. That’s why the mountains and the snowy Midwest and Northeast keep cooling through January.
Then there are the Southerners who aren’t rushing into winters as quickly as their California cousins are. Blame it on all that humidity. Just as oceans and lakes cool slower than land, so wet land cools slower than dry land. You knew that humidity was good for something besides heat rash!
El Niño is so confusing that it gives winter weather a split personality. Source: NOAA
Of course, some years, the El Niño is going to mess everything up. It tends to make the northern states warmer and the southern states colder and wetter. In fact, during some years it even brings frost and snow to the Deep South! New Yorkers have to send coat care packages to their retired Florida relatives! Meanwhile they get to put off buying mittens until the post-Christmas sales.
The question, "What is the coldest time of year?" is simply relative, anyways! For prediction of your actual local daily temperature, see Almanac.com/weather.