It is a rarity that we see these cold / stormy type of patterns persist for long periods of time through an entire season without taking a hiatus, also known as the typical January thaw. That is exactly what we will be seeing the 2nd week of January (the 12th through at least the 16th).
When looking at models to get an idea of long range weather, it is best to look at the ensembles since they consist of a mean of all the individual operational runs.
The 12z GEFS 2M temp. anomalies for the 2nd week of January nicely depict the warmer than average temperatures set to enter the eastern U.S. due to amplification of the southeast ridge.
Essentially what will be happening is the constantly favorable signal that has helped us out big time this winter will be getting suppressed, and that is the EPO going from a negative phase to a neutral or slightly positive one. You can see from the 500 mb maps above (EURO left and GFS right) that lower heights get into Alaska with a suppressed ridge sitting in the north-central Pacific Ocean. Since there is no longer warmer air getting into Alaska and the Arctic regions, arctic air will remain bottled up there while the southeast ridge draws up warmer air from the south into the northeast U.S. It also does not help that the NAO continues to remain in a mostly positive phase, meaning there is no blocking to help keep the colder air in place over the eastern CONUS.
You can see this idea of a +EPO has support from the ECM Ensembles as well.
What you can expect beginning this weekend is temperature moderating into the 40's, for the most part, with some locations likely reaching the 50-degree mark. Obviously areas furthest to the south and west have the best shot of reaching 50 degrees. I would not be surprised to see temperatures in our area not get impressively high. I think low to mid 40's is where we will be at for the most part. It has been an extreme season for temperatures so far, but it actually looks like this will be a "typical" or "average" January thaw, not one that would feature extreme mild temps with widespread 50's or 60's. The axis of the southeast ridge will remain offshore, so we will be on the western fringe of it.
Fortunately, there are positive signals out there that are showing winter returning by possibly the 3rd week of January. And if not the 3rd, definitely the 4th week. There even exists the possibility that this "thaw" only lasts for a few days and we get back to temperature departures near average or below once again. It's definitely not an impressive "thaw" to me.
We will look at the GEFS and ECM Ensembles in the long range to get an idea of what COULD happen by the end of this month.
The 12z ECM Ensembles at 240 hours show the Polar Vortex displaced in western Canada, with a weak signal of a re-surging -EPO and neutral-ish NAO. You can see lower heights are still managing to get down into the eastern CONUS though, and this looks like a cross-polar flow pattern we similarly saw in early to mid December of last month.
The 12z GEFS also at 240 hours show a much more pronounced -EPO signal with the Polar Vortex over the Hudson Bay instead of western Canada like the ECM shows. This likely allows heights to amplify more in the north Pac. and also allows a more favorable looking trough to develop over the eastern U.S. There is also a weak signal of a potential -NAO developing with positive heights extending through the Atlantic into Greenland.
Comparing these two maps from a broader sense, they actually have the same idea going with a trough getting back into the eastern U.S. and a signal of the -EPO returning. The EPO, as has been the case all season, will be the key once again for getting our snowy / cold pattern back since I do not have much faith in a negative AO/NAO couplet establishing this year. The only way I can see that happening is if a SSW (sudden stratospheric warming) event takes place, and last I checked the QBO value at the 30mb level was still positive. Real time observations suggest the QBO could be heading down, but until I see factual data, I will remain pessimistic about it.
Just for the heck of it, if we keep going on the 12z GEFS they continue to show a very favorable winter pattern by the end of this month with signs of it carrying over into February. If we can finally get our NAO into a sustained negative stage, it would really benefit us when storm threats arise.
Lastly, the CFS for January (top) and February (bottom) is pretty gung-ho about the return of a favorable winter pattern developing the end of this month into February. Although our AO has been mainly on the positive side of the scale, often times extremely positive, we have still managed to draw in extremely cold temps into the U.S. due to the -EPO bringing down strong Arctic High's.
To review...
1. The January thaw is coming, but there is the possibility it remains very short lived (3-4 days). Also, temperatures should not reach an extreme high. I'm only thinking low to mid 40's with one day possibly getting close to 50. January 11th is when I officially think the thaw begins.
2. Where the Polar Vortex actually sets up will determine exactly how our pattern after next week shapes up, but the general idea still remains trough in the east and ridging in the west.
3. Do not forget the sub tropical jet stream. Although the MJO continues to remain in the circle of death, the STJ has been a force in our weather pattern especially when it comes to the evolution of storms. SST's suggest the STJ will remain a dominant force in our weather pattern going forward. That is good news.
Enjoy the break because I am sure we will be getting right back into the tracking of winter storms again near mid-month.
-Francesco Paparatto
Please visit and register to the NJ Strong Wx forum at www.njstrongweatherforum.com
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