We are now nearly two weeks into the coldest three months of the year and we certainly haven’t seen much in the way of winter chill. Even with the recent light snow, there still isn’t any prolonged cold or snow on the horizon, so what’s up and is this going to continue?
La Niña, colder water off the coast of South America, continues to be the dominant weather driver across the Northern Hemisphere and it likely has a big role to play in helping to bring the above-average temperatures so far and the even-warmer air mass on the way for this week.
It’s not just New England that is going to be above average either. As a matter of fact, when compared to average the real anomaly is going to be in the center of the country.
Next week, some areas could see readings nearly 40 degrees above the 30-year averages. It is important to remember the 30-year averages we are now using are for 1991-2020 and are statistically significantly warmer than the 1981-2010 and 1971-2000 averages.
In other words, the warmth coming would be even more anomalously warm a couple of decades ago. Look at the area of 70s across the middle of the country; this is quite unusual for December and could be record breaking.
The warmer colors in the cycling map above represent temperatures above average. As the air flows generally west to east, this warm air moves into New England before eventually exiting the East Coast in the fourth week of the month.
All the mild air is courtesy of a jet stream that is stuck in a more northerly position. As long as the jet stream stays near or north of our region temperatures can’t go below average. You can see on the map below that the winds at high levels represented by the red are running across Southern Canada.
In addition to the jet stream, the polar vortex that is ever-present during the winter months is also very stable, not allowing the arctic air to infiltrate into the United States. The map below shows the height of the pressure at only 10 millibars, literally at the top of the atmosphere.
When these heights produce a tight gradient the arctic air has a hard time moving south from the poles. The Arctic Oscillation Index continues to be positive and it is difficult to bring truly bitter air south when this is the case.
Winter enthusiasts should not give up on winter, though.
The latest 3-to-4 week outlook, which looks out to the end of the first week of the new year, brings back colder air and turns much of the country colder.
The core of the warm air shifts south and it’s likely we are much more seasonable here for Christmas and New Year’s weeks. In this pattern it’s easier to get some snow. Let us see how it plays out.