Even before the official beginning of Winter 2017/2018 (still 4 days away), we’ve gotten off to a rather fast start, with multiple small to moderate sized snow events from the Deep South to the Mid-Atlantic to the Northeast. In fact, for many, these last 2 weeks have probably felt a lot more like the middle of the winter than the middle of December, with record breaking lows, a growing snow pack, and consistent storms back to back to back. But will that last?
Of course not. Starting this week, the eastern US will begin to feel a big change in the weather, with temperatures closer to normal and rain taking away a lot of the snow that still remains on the ground. This big swing in temperatures is thanks to a massive flip in our upper level atmospheric pattern, with higher heights dominating the eastern two-thirds of the country and lower heights dominating the west. This can be attributed to our PNA dipping negative, promoting more troughing in the west, the return of our not-so-popular Southeast Ridge, promoting more ridging in the east, and a rise in both the AO and NAO—all of which make the chances of winter weather in the eastern US drop significantly.
The west coast, however, will be feeling the opposite effects. Our negative PNA will allow for much colder air to pump down into the western United States, and a new storm track will form along the dividing axis—which will shift into the Midwest by this weekend. What does all of that mean? Higher snow chances, from the Rockies to the Plains to the upper Midwest. Guidance is already pointing to a potential snowstorm from Colorado and Nebraska to Minnesota and Wisconsin just before Christmas Eve. Further east, this would be a massive rainstorm, with warm temperatures surging northward from the Mid-Atlantic to the Northeast. This much we are fairly confident in.
It’s what happens after this brief change in the pattern that becomes a bit trickier to get a good understanding of. Around Christmas (December 23rd – 26th period), the pattern shifts once again, and we begin to see the return of our ridging out west (signaling a positive PNA), deep troughing in the middle of the US (signaling a declining AO), and warmer heights still along and offshore the eastern seaboard (signaling that our Southeast/Bermuda Ridge is staying rather stubborn). This is usually indicative of a pattern that will bring winter weather across the Midwest and interior section of the Northeast and New England. But things at this point still look transient, meaning the pattern is fluid and still changing. This could be a time-period to watch for some kind of big storm that either cuts along the coast and brings wintry weather further inland and mixing closer to the shoreline, or a storm that cuts even further west and give a big thump of snow closer to the Midwestern states. We won’t be able to figure that out for another few days at least, but it’s a time-frame we’re keeping an eye on.
Going really long range and heading into the end of December and early January, early signals suggest the possibility of another brief shot of warm/wet weather in the east and cold/snowy weather in the west, and then yet another flip towards more of what we’ve been seeing in recent times. The first week of January has the potential to revert back to ridging out west, troughing in the east, and even some blocking overhead, giving a much better shot at snow and cold for the eastern third of the US just after New Years. The long range signals support REAL Winter possibly returning in early January, but once again, making definitive forecasts this far out wouldn’t be a good idea, so our team remains rather skeptical.
For now, taking it day by day, the most important things to know are that the eastern US will likely take a relaxation period from the cold and snow from just before Christmas (where there will still be a big storm potential) until around New Years. Beyond that, early signs show it could be rather white again for the eastern US, but we’ll have to monitor this as we get new data over the coming days.
For now, stay with us and keep checking back for updates.