December-to-date is running colder than normal (to the tune of 2.2 degrees at IND), but the past (7) days has seen a flip in the frigid 1st half of the month.
December temperature anomalies, courtesy of Weatherbell.com.
Temperature anomalies the last 7 days. Courtesy of Weatherbell.com.
The “relaxation” is temporary. Modeling continues to advertise the recent “thaw” will give way to increasingly bitter times as we get deeper into the New Year. By New Year’s Day we note the positive heights continuing to establish themselves across Alaska and Greenland (cold and stormy signal). We also note the southeast ridge present, though to a lesser degree than over the past week.
By Day (10), the cold pattern is well established over the Lower 48. This is a coast-to-coast cold signal (heart of the cold centered over the west and central) depicted by the European ensemble, along with other modeling.
Teleconnections support a cold pattern returning.
The agreement amongst teleconnections is nice to see and ups confidence in the overall direction of where this pattern is heading in regards to colder than average times looming. The negative PNA correlates nicely with the SE ridge that continues to make itself heard from time to time over the next few weeks. It should also be noted that the phases of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) become more of a factor for mid and late winter.
As far as storminess goes, we’ll have to handle those as they come. The overall pattern screams towards the idea of an active Ohio Valley to interior Northeast storm track as we move forward (continuing deeper into mid and late winter, as well). That doesn’t mean one or two storms won’t bypass our local region to the south, due to strong, cold high pressure north, but the mean storm track should put areas through the Ohio Valley in the “sweet spot” from a snow perspective throughout the majority of January, and the rest of winter, for that matter. Depending on the position and strength of the Greenland Block will have a lot to say about things. Needless to say, storms cutting NW into the central Lakes should be few and far between after the New Year. Speaking of storms, we have to continue to keep an eye on the second half of next week. At the time of this discussion, the threat is still beyond the 7-day period, but circle late next week and weekend for the potential of wintry “mischief.”
Accordingly, we see the ensemble data flipping to a colder pattern over the upcoming (10) days. Note the low anomalies in the higher latitude regions today (Image 1) versus Day 10 (Image 2).
The pattern developing by Day (10) is one capable of producing another frigid regime- only January style. Cross-polar flow sets up shop and, unlike, December, some blocking is noted, as well. This can help the mean storm track shift further south. (Bye-bye Great Lakes cutters, though Mid Western and Ohio Valley Snow Lovers will find a new worry in the form of suppression potential ;-)). Individual storms will have their respected challenges, as always. As a whole, it’s a very cold, stormy look and a pattern capable of leading to an expanding snow pack across the Lower 48.