ML/NJ
The atmosphere is always twisting and turning around, chaotically, with a mind of its own. Any truly extreme event results in large part from that effectively random behavior. For that reason, the specifics of individual extreme events are not predictable far ahead of time -- weather forecasting, which is the science of predicting this chaotic component, generally doesn't work for periods beyond a couple of weeks.
But the climate sets the stage, pushing things in one direction or another and influencing the odds that an extreme event of a given type will occur. By making the whole planet warmer, human emissions of greenhouse gases increase the odds of a warm event like this one -- or its more dangerous hypothetical summer counterpart. If we define the event by specifying a fixed threshold -- some number of degrees above average for some number of days, say -- the global warming that we've already had makes that threshold more likely to be crossed.
Besides human influence, the climate also fluctuates naturally. The most important natural fluctuation this winter is El Niño, a change in the state of both the ocean and the atmosphere in the tropical Pacific that comes every few years or so. The coming and going of El Nino events happens on a pace much faster than that of human-induced climate change, but still much slower and steadier than the day-to-day weather, so it makes sense to think of it as another factor gently nudging the weather in one direction.