March 18th Snow & Rain Storm

Low pressure in the south central region in tandem with a low pressure in the midwest are going to essentially join forces and bring a potpourri of weather to the region. A secondary will also develop along the jersey coast. 
Initally the lower level cold air will be in place as the precipitation moves in from the southwest.  Temperatures will rise aloft and this will allow the precipitation initially to start as snow but change to a sleet/freezing rain scenario before changing to rain (in all but the highest elevations in PA) ..the heaviest snows will be from NY state Northwards ..but even NY state can see a change over to freezing rain .. Outside of NW NJ precipitation should be mainly rain in New Jersey.. 

And NY State.. 

This same system will be responsible for some severe weather and this will come out shortly..

Long Range Thoughts

Lets take a look at where we have been so far for the month of March

For the most part the month of March has been seasonal to above normal in the Northeast with the exception of SW PA and SE NJ and then the southeast. 

Now this is important as we try and figure out where we are headed for the future weather wise. If you look at the above chart you will see that the AO has been negative and still is negative but as the temperature departure map shows we have still been seasonal to above seasonal values. Normally when you have a - AO this allows a discharge of colder air into the USA but as we have pointed out in times past you can not figure out WHERE this discharge of cold air will end up just by looking at the AO. You have to look at other teleconnections..

The NAO was negative but recently has risen to the neutral value but it is shown to go back negative before once again rising towards neutral or positive. So you can see why the temperatures in the southeast were below normal due to the NAO being negative it allowed the discharge of colder air into the southeast. 

Factor in the PNA and you can see that it was quite positive ..so the - AO - NAO and positive PNA allowed the colder air to discharge into the southeast part of the USA. 
However, and this is important you notice that the PNA has since gone negative.. so when the PNA declined ..and the NAO rose to neutral ..despite the AO remaining negative ..temperatures were well above normal.. and you can see this in the last 7 day departures..

There is still one more teleconnection we have to look at and that is the MJO

You can see the the MJO was in phase 7 and if you look below you can also see why the southeast was cooler 

However now the MJO is back into phase 6 and this shows you once again why the temperatures have become warmer. 
So when we go back and look at the teleconnections they pretty much show why what has occurred has occurred. Now when we look into the future we see the NAO going negative , the AO going extremely negative (both these signals indicate a discharge of colder air into the USA but remember now we are in the month of March and the averages are now higher then they were in say December and Jan ) but we still need to go back and look at the PNA and this is expected for the time being to stay negative and actually get more negative. So what this implies is that the discharge of colder air will be more central and west based then east based as long as the MJO is in phase 6. 
Forecasts are showing the MJO to go thru phase 7 again so when this occurs temperatures once again would become colder then normal with the other teleconnections already in place..but as long as the PNA remains negative the brunt of the coldest would be central and west based. If the PNA were to go positive with the AO so negative and the NAO going negative this would once again put a trough over the eastern part of the country.
Keep in mind that colder then normal does not necessarily mean temperatures supportive of snowfall if and when the PNA goes positive.  Normal high temperature at ABE for example is 48 degrees...all it would imply is temperatures below normal which could mean the upper 30s or lower and mid 40s.
Also keep in mind that when the MJO is in phase 6 this also involves the southeast ridge and gives a much more likely hood of storms cutting to the west of the region which is what we see on the model guidance for around the 18th to the 20th. When a storm system cuts west of the region it allows for warm air advections and mid levels to warm and while it may initially start off as frozen likely hood with a western track is for the system to change over to a cold rainfall.

Winter Storm March 5-7th 2013

 Heaviest amounts of snow will be confined further to the south where heavier precipitation rates will occur which will allow dynamical cooling to take effect and draw down the colder air from above to the surface. Further north the boundary layer may be an issue and so you see the snow totals start to go down.. Matter of fact in the eastern Part of the state of PA into the NE Part ..we may be dealing with a rain snow mixture for some time..
We are not putting much weight of the GFS/NAM into the scenario because they seem to be to out of harmony with the rest of the guidance. 
If you are on the northern fringes of the precipitation shield you will be dealing with lighter rates and boundary layer issues..

Since we created this map the GFS has now come into better agreement with the rest of the guidance..

This storm will be more of a nuisance above southern PA and a hindrance for those from southern central PA south into MD and VA where the heaviest snows will fall..

Winter Storm Update for 26th and 27th of Feb

Taking a brief look at guidance ... We are going to look at the 00z NAM and 00z GFS along with the 00z GGEM all at 30 hours...

All guidance takes the primary low to the west of the area ..over the Ilinois, Indiana area. Meanwhile a secondary is going to develop but this is going to develop inland. This sends the 850 freezing line well to the north of the area. High pressure to the North will initially keep some lower level cold air in place ..but this high pressure will start to slide off to the east and will bring an easterly wind. So we are going to have a wide range of precipitation types from plain rain to Snow, Sleet. & Freezing rain. The areas that will be frozen will be to the north across the northern tier of PA and in the higher elevations in central PA..Its quite possible that these places could turn to rain as well ..but initially it will fall as snow and ice across those zones. Travel could become slippery. Even though we have warm air advection and winds switching to the east we still have some colder air trapped at the surface and hence despite 850s being mild the winter mix precipitation.

Current radar above shows the storm getting itself organized over the southeast part of the US . Those locations that receive all rainfall look to receive on the order of around an inch. However south of PA may see more then an inch of rain in Eastern Md..  NYC residents can expect to see all rain out of this system ..those in NW NJ can expect to see a winter mix which could leave between a T-3 inches of snow/sleet.

There after some colder air will come in behind the system and will shift the axis of the trough further to the east so the weather will quiet down some as any storms should stay out to sea. 

Pattern Update -What is Ahead?

We been trying to put the pieces together on the weather pattern and where we are heading to over the next 10 days or so. We generally when doing this rely on two things:
1. The guidance that is available 
2. The teleconnections 

#2 being the greatest tool because it is what drives the weather patterns that we have. One of the main things we are seeing in the guidance appearing is the blocking showing up. You can see this really quite well in the below figure...

We have seen this signal come up other times this season but as we got within 84 hours ..the blocking would weaken and it more or less would become a "fake block" and not an actual true blocking pattern. So we will have to keep an eye on whether this blocking indeed happens as modeled.
Now when we turn to the teleconnections we get a muddled picture. The muddled picture comes in with the MJO. The current MJO is in phase 4..

Lets look at the what Phase 4 means in the month of Feb..

Now majority of your guidance takes the MJO into phase 5 ..from there it looks a little more uncertain but it looks like it could go into the COD which is commonly called the circle of death which is when it has less influence on the weather patterns. But this is what Phase 4 looks like in March...

The following will be Phase 5 for February and then March..

You can see what happens is the Southeast ridge is very much alive in Phases 4 thru 5. This would represent a warm up in temperatures across the region.. However..it is when the MJO reaches the COD that things become more interesting. This is when the MJO has the least influence and this is when the rest of the teleconnections will become important as to whether they actually happen as suggested.
Two different sources we can turn to for the teleconnections one being CPC and one being ESRL. So when we look at the NAO we see the following...

ESRL 

 ESRL NAO shows a very negative NAO and it stays this way thru the chart .

CPC shows a negative NAO as well and majority of the ensemble members keep the NAO negative though they try to raise it up towards neutral. 

The PNA (ESRL) 

 The PNA we diverge a little bit between the two sites with the top showing the PNA as negative to start but then going positive while the chart below shows more of a neutral but members taking it positive before going back towards neutral.

The AO 

The AO is negative and is generally expected to stay negative when looking at the above chart. So we are dealing with a negative NAO a negative AO, blocking (as being modeled) and a + PNA. 
All these teleconnections point towards a colder time period of weather upcoming if they indeed come to fruition. 
However, at the same time we are going to be having a MJO in phase 4 and 5 until it moves into the COD. So in the short term we will be moderating in temperature wise but the big ??? mark comes in when the MJO reaches the CDO. 

With those teleconnections shown to be in place this would put the mean trough into the east and this would end up putting ridging into the west coast. This in tandem with a active southern Jet Stream could lead to some interesting times along the east coast for those that are snow and cold lovers. 
Just to give you an idea and this at this point and time is just for entertainment purposes only to show you the potential that could lie on the table with the blocking, negative NAO, AO and + PNA in place. This was the 12 Z GGEM 10 day map:

It should be noted that the 00z GGEM has lost this feature however but still has the trough carved out over the region. The ECM was also close to showing something big on the 12 Z run but mainly New England ended up being the jackpot in that model run. 
The question or not to whether the upcoming pattern will deliver or not is highly dependent on where the trough axis sets up. If it sets up to far to the east anything trying to round the base of the trough would end up being to far east. If it ends up setting up further west then anything that rounds the base of the trough would move up the eastern seaboard...
So in summary we will be moderating and in that moderating time we will have two mainly rain storms to deal with (outside of Northern and Central New England) but there after is where the potential lies for things to get interesting based on what is being shown right now for about 7-10 days down the road. As always though the weather constantly changes and if that blocking fails to form and the MJO re emerges or stays in the warmer phases then winter would essentially be done for PA and points south and some parts in those areas are still waiting for winter to begin!

Feb 22nd-23rd Winter Storm

Low pressure is taking shape over the south central part of the USA. This low pressure area is expected to head up towards the Great Lakes region, pushing a warm front across the area and then  drag a cold front across the region.

. This cold front will advance towards the region and a wave of low pressure will form over the southeast and move to a position off the southern New Jersey Coast. Due to the warm front moving across the region we will have what is called Warm Air Advection precipitation breaking out across the region. 
The air mass in place is very shallow across the central and western part of the state so as the warmer air moves over top of this shallow cold air it will result in some winter mix precipitation. We are not expecting a large amount of ice or snow but an inch or two of snow could fall and up to a tenth of an inch of ice is possible. Untreated roadways could become slippery. 
Further east this cold air will scour out fairly quickly due to easterly winds and warming temperatures so locations may start as a mixture of snow sleet and rain but quickly transition over to rain . Extreme Southeast PA should remain all rain.
For areas further north of PA.. we want to wait one more cycle run of the guidance to see how far north the warmer air is anticipated to advance. 
For those that live in the NYC /PHL area this will be an all rain event. Rainfall looks to be generally .75 to around 1.25 inches. 
The areas that look to be all snow would be Northern New England.. 
Southern New England looks like there could be precipitation type issues as well.. which is one reason why we are holding out one more model cycle for places further north..

Valentines Day Snow Event

With what was a historical east coast snowstorm in the past week.. we are talking about a snow event once again. However, this time around this will not be a historical storm or even a Major Snowstorm but will be more of a light to moderate event depending on where you are located.

We will start this off by saying all models essentially agree on the track of the system ..the problem is that the models do not have a lot of QPF with them. They have cut down on the QPF by having a more weaker southern stream vort and the quickness of this system.

Briefly looking at this system we will start with the wettest model and end with the driest model ..

The above is the 00z UKMET and this falls in as the wettest model and the furthest north model. 

00z GGEM has about a 7 hour window of snowfall (a quick hitter) and it starts as rain in locations like southern NJ , De etc

GFS & NAM are overall quite similar ..the one difference being that the GFS is slightly further north with the QPF shield then the NAM. 

Finally the ECM which is actually the furthest south of all the models and barely brings any QPF up towards KPHL.

When putting together the map we have left the ECM out of the equation and have used more a blend of the NAM/UKMET/GGEM/GFS.
This will not be a major snowfall as we mentioned but more in the way of a nuisance event 

We expect the National Weather Service to issue winter weather advisories for this event.