It seems like we have been talking about this system for about 2 weeks..Well not on this blog but on the Facebook page.
So lets take a quick trip back into memory lane to the month of November when we seen temperatures that were in the 60s-70s..
Quite a warm month was on tap across the region. This continued thru about the first week of December but then something happened. The pattern stepped down.
Lets use ABE for this example..
8 44 29 37 3 28 0 0.02 T 0 9.4 25 310 M M 4 1 37 290
9 48 27 38 4 27 0 0.00 0.0 0 3.4 13 190 M M 2 18 17 210
10 42 23 33 -1 32 0 0.00 0.0 0 6.3 17 330 M M 2 1 22 310
11 39 20 30 -4 35 0 0.00 0.0 0 1.1 8 270 M M 0 14 280
12 40 18 29 -4 36 0 0.00 0.0 0 0.6 7 240 M M 0 1 10 210
13 48 19 34 1 31 0 0.00 0.0 0 4.8 13 320 M M 0 18 16 290
14 51 27 39 7 26 0 T 0.0 0 2.6 9 170 M M 9 13 170
15 56 43 50 18 15 0 T 0.0 0 7.3 18 210 M M 7 23 180
16 54 35 45 13 20 0 0.00 0.0 0 10.5 29 290 M M 1 51 280
17 39 25 32 0 33 0 0.01 T 0 5.5 14 340 M M 6 8 17 340
18 35 19 27 -4 38 0 0.00 0.0 0 4.1 14 320 M M 1 17 340
19 48 19 34 3 31 0 T 0.0 0 6.0 16 240 M M 4 21 240
Now what we see is the first days of December that were well above normal but then we notice that we started seeing temperatures that were now in the seasonal to slightly above normal and some days even below normal. This is something that we did NOT see in the month of November as it was pretty much an all out blow torch. So the pattern has indeed stepped back down as we were talking about prior.
Now was there a reason for this warm weather? Yes there indeed was..
Just take a look at how positive the Arctic Oscillation was. Not really a surprise with the warmer then normal weather. However now look what has happened! These are the observations and NOT the forecast models AO predictions. The Arctic Oscillation has taken a slide into the negative territory.
Now you can see the reason why the weather has become more colder then previous because that Artic Oscillation has taken on a negative outlook.
The next part of the picture we want to look at is the MJO.
You have to look at this very carefully but you can see that the MJO is still in the COD in which it looked like it would come out into phase 4 or 5 but looks like its lost the progression. Essentially when the MJO is in the COD it has less of an influence on the pattern and makes the other teleconnections more in play.
So presently as shown above we have a – Artic Oscillation a + PNA (on the CPC charts) and a positive NAO.
So what this means is that with a + NAO we really have no support for a storm to go southeast and out to sea AKA the GFS model camp. However with a positive PNA and a – AO we do have support for a trough to form in the east and ridging to arise in the west.
So lets take a look at the models. For the purpose of this discussion we are not going to look at the GFS because we like to look for consistency in the models and then go from their.
So here is the 12 Z GGEM. As is the bias of this model when it comes to the phasing of storms it tends to over phase and over amplify. Northern stream and southern stream phase together and bring an inland runner.
UKMET shows a storm developing in the GOM and then it essentially takes a track very similar to the ECM and blows up a storm .
So we have two models that are showing amplification of the weather pattern and one model not posted (GFS) which simply slides south and east and never really even develops the storm.
Lets move on to the European Computer Model which has shown consistently a solution very similar with very little alteration in evolving and track. Timing has changed on the ejection of the shortwave energy but other wise its been consistent..
And the result of that run is as below:
As you can see the ECM is showing a solution cold enough to produce snow across the vast majority of the region delivering a White X mas to the vast majority of the region.
Does the ensemble means back up the model ? Well 120 hrs. never updated but we will rely on Pro Met Bobby Martrich from Lehigh Valley Weather Patrol and his response to the question is as follows:
“Lehigh Valley Weather Patrol with Bobby & Suzy Hour 120 and 132 also support it. Looks to be a tad colder at 120 and 132 than the operational.”
And we can basically confirm this at 144 hours on the ENSEMBLE means as well:
So with all the above shown and discussed we like to go with a solution that has shown consistency. This solution has been the European Computer models which even has the backing from its own ensembles…
What can go wrong? The low pressure can end up being more amplified while in the GOM region and cause a stronger height rise along the east coast which would result in a shift west ward with the zones as shown above.
This is only a scenario map based on the most consistent model and its ensemble means which fits the teleconnections discussed above.
Stay tuned for more information as this gets closer!
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