INTRODUCTION
The writing has been on the wall, hasn't it?
*Multiple coastal storms this Fall of varying intensities and complex set-ups that even guidance has struggled to figure them out
*Arctic blast in November just before Thanksgiving
*A couple failed SSWE's (Sudden Stratospheric Warming Events) but the fact they keep re-surfacing goes to show which direction this pattern would like to go in for the ensuing winter
*Projected "warm-ups" have been short-lived and normal to below normal temps. quickly takeover the regime once again
This is a clear indicator to me that Mother Nature is trying to toy with us a little bit before our official winter pattern gets here. For those who read my winter outlook, you will understand that the predominate upper level winter pattern I am expecting is a -NAO/-AO couplet teaming with a +PNA and a mainly transient EPO phase. And to those who follow me on my forum, you would also know that the time period between December 20th and January 10th was when I expected the weather pattern to turn favorable for wintry weather. By analyzing current long range guidance, we will be able to see we are heading in that direction and the period between Christmas and New Years could present itself with a Godzilla.
I want to quickly address the December 17th and 21st storms before I get to the interesting time frame the end of this month.
December 17th & 20th-21st Storms
00z GFS:
The storm this Wednesday afternoon is expected to bring little precipitation to the area. Probably less then half an inch. The reason why it needs to be brought up is because it can help set the stage for a possible coastal storm between the 20th-21st. You can see by looking at #1 from the image above, the energy associated with the mid-week storm is sheared out and does not organize itself until its in northern New England or southeastern Canada. #2 is the next piece of energy coming onshore that will help form the 20th storm.
If we fast forward to the 20th time frame, you will see the GFS handles this storm pretty different from the EURO, which I will talk about next. This model believes this storm is more of a SWFE (Southwest Flow Event) by maturing the energy in the Midwest and shooting it into the northeast. There is not a true phase between the southern and northern stream branches. #1 shows the core energy I am referencing in the Midwest. #2 is a result of #1, with energy shooting to our northwest this helps heights to rise along the east coast and keep temps. above freezing. #3 shows the cut-off ridge in eastern Canada which is preventing this storm from working with a true arctic air mass. #4 is the 17th storm, and as you can see it has situated itself in southeast Canada as an upper level low. This is key because if this ULL is able to hang around it could turn into a 50/50 low for the 21st storm to work with.
00z EURO:
By looking at the 00z EURO you will see what I mean about these models looking completely different at H5. The EURO digs the southern stream energy much more than the GFS (marked #1) with a very noticeable northern stream energy (marked #2). A nice ridge spike in the west as well, labeled #4, to help drive that northern stream energy toward the STJ. #3 is the 17th storm which is now acting as a 50/50 low. A 50-50 low (located at 50* lat. and 50* long.) helps block east coast storms from escaping out to sea. Usually there is an area of High Pressure located west of one, and it just so happens that will be the case this go around (#5).
A rex block is defined as an area of High Pressure located directly above a Low Pressure system. This may not be a 'true' Rex Block set-up shown here from the 12z EURO, but one can argue it's a pseudo looking one. Since air is flowing from north-south, there is not much in the way of eastward progression, hence the terminology "block." What I see this doing with the storm around the 20th, coupled with the possible 50-50 low, is helping the H5 energy consolidate around the Mid-Atlantic and help form a coastal storm. I think the GFS is struggling with the various elements in the upper air pattern at this time frame and is simply clueless with how to handle it all.
So taking all that into consideration, you will see how the EURO eventually plays out the rest of its run. It has a coastal storm off the coast with a closed off H5 (#1). To the north we have our blocks with the 50-50 low (#2) and ridge (#4). If the Euro solution is right, and I am learning toward it more than the GFS at this time, this could be a significant snowfall for area north and west of I-95. Areas along and south and east are also still in the game for snow, but we have to see exactly how much cold air the storm will be able to work with. Keep in mind Canada will be seeing temps. running above normal this week so the cold air source is not so great. This storm will have to manufacture some of its own cold air through dynamic cooling if it were to occur. And you're probably wondering what the heck #3 is? Well that is the next storm coming onshore off the eastern Pacific and you can already tell where this pattern is headed, cant ya?
December 20th-21st Final Thought's
I think there will be yet again another coastal storm to track. Where the rain/snow line sets up will be the questions on everyone's mind. I do think this storm will see much more in the way of snow accumulation for the northeast region in general compared to the last one, which largely became an upper level low just circulating and rotating snow bands into the area. From a climatology standpoint, this storm will also favor more accumulation simply due to sun angle this time of season which helps with the surface temperatures. So that is what we will be tracking this week. Please make sure to follow the forum!
Godzilla Potential Between Christmas & New Years
Hype, hype, hype blah blah blah I do not care. I'm not exactly calling for a storm of this magnitude in this time frame, but I REALLY like the potential for one. I think once the 20th storm is over and done with, I think our true winter pattern finally gets here.
Lets do a quick check up on SST's key regions.
SSTA (Sea Surface Temp. Anomalies) are running well above normal off the west coast into the NE PAC. and the GOA. This is a classic +PDO signal that will help initiate a +PNA. I also think the cool pool over the central Pac. will help keep a mean trough centered over the Aleutians, which is good for helping to pump up heights in the western U.S.
Warm-Cool-Warm...that is how the SSTA configuration is set-up in the north Atlantic Ocean. As discussed in the winter outlook, this is a classic look to signaling a -NAO. We have not seen some high latitude blocking for quite some time, but I finally think that streak comes to an end by the end aforementioned time period.
The latest 00z GEFS are just honking the horn, loudly, for a great winter pattern to set up for the eastern CONUS around Christmas. The Aleutian trough is centered right where it should be during +ENSO events, helping to form the -EPO/+PNA tag team. We have a -NAO, more of a west-based, with positive heights extending into the arctic.
The 12z ECM ENS were also barking in this time frame with the signals I just talked about. A classic retrogression of all the upper air anomalies back to where they should be during -QBO/+ENSO/+PDO episodes.
CONCLUSION
You've heard the saying "patience is a virtue" and it truly is in the weather world. A lot of folks were getting a little uneasy at the end of November when they were looking at long range guidance showing little promise with regards to the NAO. And then there were a couple failed SSWE thrown in there as well...this really raised the suicide bar high. But everything is coming together as expected and history shows this type of weather regime takes time to form.
We shall see what happens!
Francesco Paparatto
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