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.”
We note ensemble data is suggesting high latitude blocking tries to develop towards Day 10. Recall this was the missing ingredient in the bitterly cold blasts of air that occurred during the first few weeks of December. Both the GEFS and EPS agree on the increasingly blocky look to the pattern by Day 10. This would help drive a cold, stormy pattern by early January. Instead of storms cutting, we would see more suppression. With a “stubborn” southeast ridge, things could get interesting across the Ohio Valley from a wintry perspective….
We don’t want to jump the gun, but it the positives can “hook up” over the pole, we stand the chance of locking into a rather lengthy cold, snowy regime as we rumble deeper into the heart of winter.
Summary: A rather mild regime remains as we rumble through Christmas before trending more seasonable next week. From a wintry perspective we need to continue to keep an eye on the period around New Year’s Eve/ Day. Confidence continues to increase on the potential of a return of arctic air come early January.
This is, of course, is in stark contrast to December 2015.
As we move forward, an active pattern awaits between now and the end of the year. This comes after a few days to catch our breath, including moderating temperatures leading up to Christmas.
Christmas Eve will feature overcast skies with areas of fog and drizzle, but the majority of the concentrated rain should fall south of the region. Santa’s ride into central IN should be uneventful, weather-wise.
Temperatures will fall through the day Monday and we should run much closer to seasonable temperatures next week. A couple of additional storm systems will have to be monitored for rain and snow prospects the middle of next week and again around New Year’s Eve/ Day. Initially, we’ll be rather mild, but there may be more in the way of cold air readily available to make the storm system around New Years “more interesting” from a wintry perspective.
