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?
Right, California, your coldest days are in December! Wrong, Massachusetts, your coldest days are in January! Welcome to the confusing winter weather of the USA.
NOAA, the weather people, just reissued their map of when the 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
That 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 all of you Southerners – you aren’t rushing into your winters as quickly as your 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, this year, 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.
So winter is not only cold, it’s confusing. And with this year’s strong El Niño, it just got even more confusing.