Revised & Final Map For Dec 29-30th 2012

This is the general consensus of the weather models tonight and when you take a blend of the models this is what we think the end result should be. This system should definitely be cold enough to support all snowfall across majority of the region with the exception of being southern De where it could rain but end with some snow...
We will have to keep an eye on the two jet streams to see if there is more interaction of the two. As of now they are expected to stay separate which makes the coastal get going to late to deliver the region a heavier snowfall...

December 29th-30th Winter Storm

Another storm system is on the way for Saturday for the Mid Atlantic and Saturday into sunday further north... Right now this is just a Preliminary 1st call and this will be updated later tomorrow.. A general 2-4 inches across the state of PA and into NJ...

December 26th and 27th Winter Storm Update

First off we want to wish everyone a Merry Christmas for those who do celebrate the holiday. It has been 10 years since ABE has had a white christmas and with last nights snowfall followed by freezing drizzle, which left 1.5 inches we can officially say that we had a white christmas for 2012.

For snow lovers that will NOT be the end of it .. There is another storm system that is developing over the south central states.

This system is responsible for severe thunderstorms today and the potential for some strong tornado's which we discussed on our Facebook page.
Lets look at what the guidance does with this system and we are going to start with the GFS because the GFS by far is the warmest model that is out there...

The GFS would start as a period of frozen in places like East Central PA etc but then it would end up turning over to ice and then to plain rain. The only other model that is probably as warm as the GFS is the NAM, which will not be showed here because it is still beyond the 24 hr window.

Lets look at the rest of the guidance and what you are going to notice is that the rest of the guidance is actually colder then the GFS..

 European computer model is actually colder at the approach of the storm then last nights run but would still imply a change over to ice and probably rain..

 The GGEM above is actually colder then the GFS and now this should be considered a red flag to the GFS because generally speaking the GGEM is a rather warm biased model and the very fact that it is now colder and also more southeast raises questions to the track and the air mass in place.

The NOGAPS which not that many people look at outside of us and the HPC..has actually trended more south and east and this is actually colder then its run last night. Last night was virtually showing nothing but rain but this would indicate snow/frozen to rain back to snow/frozen.

Last but not least is the UKMET which is above which also is showing a colder system. While we do not have the in between hours we can pretty much figure that it would be similar to the other guidance above and this to would indicate a longer front end duration of snow and ice before a changeover to rain.
Now lets turn to a little nowcasting for this storm system to lay the final pieces in place...

This is the current pressure fall maps and we have put an " L" where the area of low pressure is by the deepest pressure falls. This is further east then what the GFS had indicated it would be at 18 z. So what this tells us is that it had not made the NE turn as soon as what the GFS was indicating and has allowed it to make it a little further to the east. This should start to make its NE turn but remember because of being slightly further east ..this means its going to end up being slightly more south and east as it makes that turn to the Northeast. Which means as it moves up towards the region it should be more south and east then what the GFS anticipated which also means it would be slightly colder then what the GFS is anticipating.
So at the top of the page we have come out with a scenario map which basically shows where all snow should occur and where rain would occur and the battle zone in the middle which may be dealing with snow to sleet/zr to rain.
The all snow zone should be on the order of upwards of 8+ inches of snow..perhaps some sleet mixing in..
The next zone we feel should be on the order of 4 to about 8 inches of snow /sleet followed by what could be a longer duration of freezing rain because CAD (cold air Damming) likes to hold on longer....
And then the other zone is the rain zone where we could see about 1-2 inches of rain occur.

We would not be surprised to see a slightly more south and east shift tonight on the 00z model guidance because of the observation discussed above.

Mid Week Storm and Pattern Update ..X Mas Eve Edition!

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 :) 

Pattern ..Where are We Going?

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.