The El Niño is significant to say the least. In the map below (and you can click on any image to enlarge it), I've highlighted the area that is monitored for El Niño and La Niña. Water temperatures are right at 3° Celsius warmer than normal in that region, and this will likely be the strongest ever recorded. While 3° degrees may not sound like much, it has a profound impact on the weather pattern. It also impacts wildlife and fish behavior, which brings up other topics of discussion that we won't get into here.
One of the other factors taken into account for this long range prediction is the Arctic Oscillation (called "AO" for short). I've mentioned it before here on the blog, but just as a refresher, here's why it's important. When the AO is positive, we generally have milder stretches of weather because the bitterly cold air is locked up near the Arctic. When we see it go negative, the eastern two-thirds of the country become quite cold and it can last for a week or two at a time. In fact, it can be warmer near the Arctic than in the US when we see a negative trend in the AO.
Given that we've had such a positive AO this fall and still today, I'm leaning more toward this trend throughout the winter. Sure, there may be some occasional instances of it going negative and it getting cold for a bit, but the overall thought is that we will end up positive for much of the winter. Therefore, I'm leaning toward above normal temperatures throughout the winter.