Tank tops and shorts for Christmas? You might be wondering why we have not had our usual snow dump here in New England, or anywhere else up north for that matter. But it’s not just the northern U.S. facing warmer-than-average temperatures for the winter; new reports from the National Oceanic and Atmospheric Administration (NOAA), note record warmth in the Western United States, as well as portions of central Siberia and eastern Mongolia.

But why is this happening?

It basically comes down to a phenomenon of complex weather patterns resulting from variations in ocean temperatures in the equatorial Pacific named El Niño and La Niña. These warm and cold water oceanic currents are opposite phases of what is known to scientists as the El Niño-Southern Oscillation,​or the ENSO cycle. The ENSO cycle describes the fluctuations in atmospheric and oceanic temperatures in the eastern equatorial Pacific ​t​hat have a major impact on world climate. “Typically warmer than normal temperatures cover the northern third of the U.S. and cooler than normal across the southern third,” said meteorologist Dr. Michael J. Dickinson. “However, not all El Niños are the same. This year, the eastern half of the country has been warmer than normal so far.” In years with a strong El Niño, warmer temperatures are expected for the western hemisphere, and this year is no exception. Researchers have confirmed that this year’s El Niño is one of the strongest on record, which helps to explain those crazy warm temperatures in December.

The most frequently asked question about the warm weather is: do these abnormally warm temperatures have to do with global warming? “The official answer is maybe,”said Dickinson. “One should not try to associate a single event or a single season to climate change. Just like having a snowy winter last year does not disprove climate change in any way [warm weather alone typically does not prove global warming], weather happens. Some years we have a lot of snow, some years we don’t. El Niño has much to do with our current weather pattern.”

Another weather phenomenon worth noting is the jet stream. The jet stream is a narrow zone of strong winds in the upper levels of the atmosphere that helps to steer weather patterns. The jetstream also tends to separate the cold air to the north and warm air to the south. Temperatures remained above normal for most of December because the jet stream was well north of most of New England, keeping the cold air up in northern Canada and the warm air below in New England allowing for unseasonably high temperatures. If the jet stream sinks to the south, temperatures will begin to go back to their seasonal average.

But with the onset of snow on January 4, and temperatures slowly but steadily creeping down; it is safe to assume the reign of El Niño has come to end for New England. But, as New Englanders hunker down for the frosts of February, the fear of missing school due to massive snow storms is gone, and parents can happily send their students to school knowing that they will focus on their education and not daydream about a massive snowstorm permanently cancelling school.