A women walks out of a New York subway stop.
A woman pulls up her hood as she exits a subway during a snowstorm in New York City, March 5, 2015. REUTERS/Lucas Jackson

For all practical purposes, winter starts at around the moment your heating fails, forcing you to put on all your ugly Christmas sweaters at the same time. For others, it’s when you slip and fall down a dozen stairs into the subway. However, smart people at the U.S. meteorological society say wintertime officially starts Dec. 21, at 11:48 p.m. EST, in line with the astronomical calendar.

Despite nearly record-breaking high temperatures in December this year, the Weather Channel predicts in its 2015-16 winter outlook that the East Coast will be colder than last year. However, for New Yorkers and others in the East who might be bracing for the next apocalyptic snowstorm that could shut down the entire region and threaten life on Earth as we know it, you're safe until late January or early February, as warmer-than-normal temperatures are expected throughout December and early January.

However, other weather experts claim the mysterious and unpredictable El Niño, which the National Oceanic and Atmospheric Administration has said could be at its strongest this year, might mean mild weather right until the end of winter in March.

"The strength and location or 'flavor' of the El Niño event suggests that a very warm 1982-83 or 1997-98 winter is quite possible," said Dr. Todd Crawford, WSI chief meteorologist. "However, there is some risk of big blocking this winter, driven either by a premature weakening and westward shift [toward the dateline] of the El Niño impacts or by just a general tendency for stronger high-latitude blocking. While this blocking potential does add colder risks for the upcoming winter, we are still leaning towards a slightly cooler variation of the very warm 1982 and 1997 strong Niño events."

So essentially, experts are predicting a milder early winter unless El Niño changes course at the last minute. Keep your sweaters on standby.