Let us start this off by wishing each and every one a very merry christmas from Down to Earth Weather forecast center.
We have been off the computer for a little bit of time but we are now back and we are going to be discussing the pattern as well as storm potential for the midweek system. Before we get into that though lets take a look at where we have been...
No doubt it has been a very warm december with temperatures well above normal across not only the Northeast but majority of the country. This is a far cry from what was anticipated to happen for the month of December. We are actually over the next couple days going to be re looking at the winter forecast and chances are pretty substantial that we are going to have to issue a revised outlook. We did this last year and it looks like it may be the case again this year.
So lets look at the guidance with the upcoming storm system and again if you are a snow lover you are going to have to according to the guidance be pretty well north in order to obtain any snow (snow that would be substantial or major) ..
GFS as you can see has the system after initialing bringing some frozen move inland and changes everything over to a cold rain. Now normally we would say "Hey its the GFS"... but truth be told its not alone..
It has support from its ensemble means. But even still the GFS and GFS ensembles are not alone either..
You can see the GGEM as well takes this into south central PA and turns all of the southern half of PA into rain including east central PA and almost all of NJ ..again this is after some initial frozen precipitation.
The UKMET is really not that different from the above models that we just looked at ...
And as you can tell the NOGAPS is also very similar to the rest of the guidance and would have the frozen precipitation well inland (west and North)...
Last but not least is the ECM
Here is 78 hours and you can see that even the ECM brings precipitation issues even into the poconos.
So what is the problem we may find ourselves asking. Why is it that we may start as frozen and change over to a cold rain.
Lets start with the fact that we have not had very much cold air this whole month of December..
Lets take a location like Allentown PA for example where on the 23rd the high temperature was 41 degrees. This is STILL 3 degrees above normal for the high temperature. So while it may APPEAR colder we are still warmer then normal.
Another factor is the teleconnections and this ties into the pattern as well. While it is true that we have the NAO negative...
And while it is true we have the AO negative...
We have two other factors that are working against us.
The PNA is neutral Negative . Simply what this means is that any storm that tries to come across the country or up from the southeast is going to try and cut because of that negative PNA.
And we also have a neutral EPO (present ) but at the time of the storm- positive EPO.
We also are seeing a track that is taking the system literally across Southeast PA and across the NJ coast. And a interior track like this is never what you want to see for an all snow event. Can this change? Yes ..However..at the present time it would be foolish to forecast an all snow event unless of course you are well north into NY State for example or into Western PA like the Pittsburgh area.
We do though see some hope when looking at the 850 temperature anomalies and that is we no longer see a Alaskan vortex... However..the teleconnection combination you want to see for a snowstorm as well as a pattern change is for the following teleconnections to occur.
1. A positive PNA
2. A negative NAO (preferably west based)
3. A negative AO
4. A negative EPO
That is the combination of what you want to see ... that is what you want to keep an eye out on.
As for this system it looks to be mainly wet then white ...outside of the northern tier of PA and further north.
Though we do not put much stock or faith into the images this is just to give you an idea of what the ECM sees in a three hour time frame wed evening...
On a brighter term for those winter weather lovers we just may have to wait for the next storm. Since this is like three waves of low pressure over the next 7 days (first one being a minor system and nuisance Christmas eve into early morning Xmas) and then the midweek storm and then perhaps the weekend ahead...
This one would indeed be cold enough for snowfall..However..lets get thru the midweek system before we talk about that one :)
Before we can begin to look at where are we going we have to look at where we have been...
This is what the month of November looked like. As you can see we had some well below normal temperatures across much of the region.
People keep talking about a pattern change...however...what they do not realize is that we have already had a pattern change...
Let me show you what i am talking about...
Quite a contrast from the month of November one would say for the first 4 days of the month of December.. The change in the weather pattern has been due to the exact same thing as last winter and that has been the return of the Alaskan Vortex. What this does is this keeps lower heights around Alaska and colder temperatures and warms up the USA (in general)..
So we have already had a pattern change but there are folks that are looking to another pattern change and this is to one of much colder weather.. And this is based on the American Model the GFS..
Here was the 12 Z 850 Day 11-15 temp anomalies
No doubt about it that is COLD...
What about 18 Z?
Not nearly as cold as the 12 Z but more normal temperature departures...
What about the 00z?
Somewhat colder then the 18 Z but still not as cold as the 12 Z...And the ensembles for the same time frame..
Cold departures are kept over the Northern Plains and hint hint back into Alaska.
However , more important what about the change in just 12 hours from 12 Z to 00z in those 850 temperature departures?
Yup even the GFS guidance is getting warmer in the 11-15 day range time frame compared to just 12 hrs ago.
So now lets look at the ECM and we are going to look at the departure maps for the entire run minus 168 hrs because that image did not come out...
As you can clearly see the 850 mb temperature departures across the region are above normal and by 240 once again you see lower heights coming into the alaska area.
So the European guidance has a brief shot or two of colder air but mainly above normal departures and the GFS compared to 12 hrs ago has warmed up.
So we see what the guidance says but what do the teleconnectors tell us...
EPO is presently negative which can help to bring colder air into the USA but as you see it is expected to go positive. Which for colder air you would like to see a negative EPO sustained..
The NAO is essentially neutral to positive here...and again you want to see these charts showing the NAO in the negative column and you want to see this to get sustained cold in the area..
The PNA ..
The PNA is negative and pretty much other then a couple temporary spikes we look to be dominated by a negative PNA.
With the alaskan vortex in place this will put places like Alaska below normal. With the - PNA this is going to center the cold from the Northern Plains into the west coast by putting a trough on the west coast into the northern plains region.
You can see that CPC is also on this same page as we are and again this is largely due to the teleconnections taking place..
And clearly you can see that Alaska and the west coast is colder or more normal while the east continues to be in above normal weather.
Until that Alaskan Vortex is removed and we get switch to a west based - NAO along with a + PNA ..we will continue to run the risk of higher then normal temperatures with only glancing bouts of colder air.
Now that the storm is winding down...What is on the horizon? With the AO rising and the NAO rising and the PNA still negative ..a warm up is on the horizon with temperatures being seasonal to above seasonal for the first week of December ..In about ten days troughing could return to the east coast....
Warm air advection snows will be moving across the region starting in the overnight hours... and thru the day on tuesday. This snowfall will probably have a difficult time sticking on anything other then cars and grassy areas because of the time it will be falling...
You can see the QPF that HPC thinks is possible over the next 1-2 days...
As far as guidance is concerned the NAM is the wettest ...
With the GFS mainly showing .25-.50
As we discussed earlier in the day the best dynamics seem to be setting up across Southern PA into east PA and into NW NJ. I think we can see snow into NYC but we feel generally this would be a mixed event due to the lighter precipitation expected across that region.
This will be more of a nuisance storm then a disrupting storm however for those of you who are snow lovers this is something that we were missing last year for the most part outside of Octobers big snowstorm.
It is possible that if the NAM's wetter solution ends up correct that the 2-4 zone could end up a 3-5 zone so we will just say there could be lollipops to the 3-5 range anywhere with in that zone...
All afternoon we have been analyzing the models and guidance as they have been coming in. Just less then 24 hours ago we had the models essentially all saying that this was going to stay far enough off the coast that it would not really effect anything other then the ocean. Alot of the people around the internet bought that scenario but we never bought into that scenario. There was only two models that we were watching for signs or hints that would tell us or help us to come out with a forecast . Those two models were the European Computer Model .. this is the only model last night that did actually not take the system out to sea. The other model we were watching was the NOGAPS. We watched the NOGAPS to see where it was positioned with the low and we mentioned on our Facebook page how the rest of the guidance was holding hands with the NOGAPS. This told us that the guidance was to far to the east which left the ECM being the only model that was west of the NOGAPS. So at that point and time we were banking on two things to happen.
1. The ECM to end up being the more accurate model since it was west of the nogaps ..
2. The rest of the guidance to start trending back towards the west
This is exactly what started happening at 12 Z model runs today...then the trend continued with the 18 Z Model runs...
We are briefly going to look at the models that came out today..Starting with the 18 Z GFS...
You can see that the 18 Z GFS has definitely come west and in comparison to last night it has come quite the distant west and almost brings 1.00 liquid equivalent into the Allentown Bethlehem Easton region...
Again the above now is the 18 Z NAM which ..at 12 Z runs it had come west but the 18 Z is even more west then what the 12 Z was. Again bringing some decent QPF into east central PA into NJ and NYC...
Now in addition to this we have the 18 Z RGEM..
As you can see the NAM and the GFS are not the only models that have shifted west and bring more QPF into the region but we have the RGEM doing the same. All this guidance essentially agrees that the KPHL to Southern New Jersey and N DE are going to be the jackpot area.
Going back to the 12 Z model suite we will look at the ECM and the GGEM..
The above is just a one hour frame ..you can go thru the rest of the images at the following link (click here) ..This brings heavy snow into Eastern PA ..
The above is the 12 Z ECM images and as you can see this has indeed also come back more west compared to 00z last nights model runs.
Some things to keep in mind ...
1. The air mass that is out ahead of this system is not a warm air mass. This means that the ground is not all that warm..So we think if the snow comes down heavy enough it will stick on the pavements and the streets that are not pre treated..
2. With guidance clearly suggesting more QPF then what the NWS is projecting we can not be in agreement with them.
3. This is going to be similar to last October where we are expecting a heavy wet snow that will paste to trees.
4. This means that we could have more trees down and power outages.. So something you may want to prepare for if worse comes to worse.
5. We will have winds that will be 15-30 mph and gusts inland as high as 45-55 and along the coast we could be gusting as high as 60 mph. This in combination with the snow could mean power outages across the same region as Sandy just got done tearing up...
7. Lollipops are going to depend on where the deformation band sets up. It is in this region that we could see locations from 6-8 inches. At this time we think it could be from extreme SE PA to Southern NJ and northern De.
However..if the storm shifts west more at 00z this could end up moving that axis of heaviest further to the west...
So with all the above said...blending the models and there QPF together we have come up with the following map:
On the southern part of the T-3 inch snowfall we think it could start off as rain and be a wintry mix.. Also along the eastern NJ coast line...
Lets start this off by saying that our thoughts and prayers continue to go out to those that are still suffering from Hurricane Sandy and those that are still without power from her as well. We understand the dilemma that you are going thru .
We also think that because of what happened with Sandy and what people are going thru they are kind of in denial about what could possibly happen with the next storm system...
However, here at Down to Earth we can not look away just because the guidance may be starting to suggest something that we do not want to see. While we are hoping that this next storm does not have any setbacks to those recoveries going on we feel that mother nature goes on and so must we at Down To Earth forecasting center...
And so this brings us to the present situation of which has to do with an upcoming potential Noreaster which would effect the area wed night into thursday.. which after this storm system then things look to warm up so I guess you could say that is the light at the end of the tunnel that may become a little dimmed in the near term..
We have been steadfastly following the guidance as well as reading things around the internet and one thing i need to address is this:
1. I was reading earlier yesterday that we should not be looking at the 850 mb temperature map to come to any forecast conclusions. Well this is simply wrong. 850 mb temps are the temperatures that are about 5000 feet up in the air. So if you have cold enough air in the upper levels and surface temperatures in the mid 30s..if precipitation is hard enough it can pull that colder air down from above to the surface and allow the precipitation to fall as frozen because it drops the temperature at the surface. This is what is called Dynamics in a storm system.
A. For example of this one only has to look back to last year at the end of October and the air mass ahead of the storm was warmer (then the present one) but the 850s were colder and what happened was Dynamics took over and we had a Historical East Coast Snowstorm at the end of Oct 2011..
With that said lets begin this with what we have had in place and been using as a tool for the past couple years and it really has not let us down to this day. That would be to look at the NOGAPS for the upcoming storm system.
Now remember this is a very progressive biased model and this is what its showing at 84 hours out..
You can see here that the 00z NAM is very similar to the nogaps in at least the position of the low though of course there is timing difference..
What about the GFS?
GFS is actually pretty much on par with the NOGAPS (progressive) however it is further to the west then the NOGAPS.. (which in using the NOGAPS as a tool it should be further west) .. However one can see that the GFS is kind of on the warm side...
00z UKMET is even more progressive then the most progressive biased model but one thing you can take away from this is that the 850s are colder then for example on the GFS...
And you can also see how all three of these models are very similar overall to the NOGAPS...
We still have two models to look at yet and the next one is the GGEM...
You can clearly see that the GGEM is showing what would be a tightly , solidified Noreaster with interior snows and coastal rains. Keep in mind here that the GGEM is colder then the GFS and usually the GGEM is a warm biased model. So that drops a little hint as to the thermal profile on the GFS with it being to warm.
However this is where it now begins to turn interesting. For about 9-10 runs in a row we now turn to the European Model and this is the model that consistently called for Hurricane Sandy to take a left turn and into east central PA and that was the end result.. So now w hen we look at that model we see the following..
What we see here is not only consistency again with the track of the system..but we also notice the following:
1. A tightly would up organized Noreaster..
2. Much colder at the 850 level and colder then the 12 Z run..
3. We see much of the precipitation in the interior is in the form of frozen and on the order of about 4-8 inches of snow...
Folks it is really hard to go against the ECM when it is at 72 hours out and due to this in combination with the GGEM we have come up with an early scenario map of how things could potentially play out ..More or less a rough sketch and we listed potential impacts to according to the 00z ECM...
What is happening as well is the better dynamics are actually going to be south of the NYC region . This is where if these dynamics occur the better chances of snowfall will occur. As the storm moves further to the north it occludes and it then begins to weaken...
We are not going to put any specifics at this time range but we will note that this system has to be watched very carefully because it will be impacting regions that were just hit by hurricane sandy.
There is still the possibility that this could go out to sea and not effect the region but with the ECM in its prime time range we think those chances are much smaller..
Again this is just a preliminary scenario map which is subject to change but it is made with the purpose of trying to prepare people for what could be a decent pre winter storm interior and for some heavy rains and winds along the coast. We will update this again 24 hours from tonight!
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