Christmas is on the way, and the question that seems to be on everyone’s mind is if there will be a white Christmas this year? With all the most popular holiday songs depicting snowy landscapes and cold weather, let’s dive into the climatology of white Christmases from the Northeast to the Midwest and your chances of seeing one.
First off, what is the actual definition of a White Christmas? It’s defined as having a snow depth of an inch or more on the ground on Christmas morning. Therefore, it doesn’t need to be snowing on the day to have a white Christmas, contrary to what many believe. The farther north you go, the better odds you have of seeing a white Christmas. Places near Boston see white Christmases around 20-25% of the time with odds improving to over 40% across the interior Northeast from Hartford, CT to Scranton, PA. Meanwhile, white Christmases only occur around 10% of the time into the Mid-Atlantic. Moreover, if you really want accumulating snow on Christmas day, your chances reduce to 10 - 20% for most and less than < 10% into the Mid-Atlantic (sorry to be a party spoiler). The white Christmas percentages are higher once you head into the Midwest, especially towards Chicago and into lake effect snow regions, where probabilities run mostly between 20 and 40% for an inch or more on the ground. Odds for measurable snow falling on Dec. 25th are also a bit higher than the Northeast, typically 20 - 30%.
Now that we’ve gotten into the definition of a white Christmas, how much more or less likely are we to see one this year across the Northeast and Midwest? We have been calling for a milder December for quite a while now, and that forecast looks to hold true through the back half of the month given the upcoming pattern.
The main reason for this warm pattern during Christmas week will be an overextension of the Pacific jet stream due to weather patterns near Asia. The Pacific jet stream usually remains situated closer to Japan, but it recently has been extending further east and leading to an inundation of maritime air across the United States. This type of pattern scours out low-level cold air, which is not good for snowfall prospects. This was origininally not thought to be the case, but the jet proved to be a lot stronger than was thought a week or so ago. Although we are seeing a weak stratospheric polar vortex (SPV), it is going to take time for that to have an impact on the pattern… a weak Polar Vortex can help lead to spells of Greenland blocking (-NAO) and cold air intrusions, but that will have to wait until further into January. It is worth noting that strong El Niño Decembers are often quite hostile and don’t really say much about the rest of the winter.
So, overall, it’s favored that we’ll see warmer than normal temperatures across the country around Christmas, not just in the Northeast and Midwest. With most systems more wet than white leading up to Christmas, travel plans should remain on target. As for a transition to a colder pattern, we'll have to wait until early to mid-January, which is typical of El Niños winters.
