1530  EDT   18  APRIL    201204.18

HPC official   Day  1-5  rainfall total forecast is pretty impressive with regard to the event coming up the East Coast late this weekend early next week.  They show a large areas of 1 to 5 inch rains which is what I was talking about earlier in the week.

This is a pretty good indication that the forecast of holding  without a lot a changes but there are still some issues of uncertainty here  which  mainly  centered around

1 the track of the   surface  Low   up the   coast
2 and the  the  Upper  Low  and Vort max   in the base of the trough Sunday Morning.

It is essentially these two features   of this event which will determine  the potential for any sort of significant severe weather outbreak    in NC   VA  MD  DE    eastern PA    and NJ/ NYC.

In my first posting on this event over on the FACEBOOK/ wxrisk.com  page my initial belief and concern is to play up the severe weather threat  in addition to the idea of heavy rain especially for the area from    RDU to   PHL.     The weather models on Monday–   see  these two images — clearly showed that the phasing between the Upper Low over the Gulf coast and the    Midwest trough   ” digging :” into  the  SE states would grab the  surface LOW  and  pull  it  NORTH … NOT  Northeast.  This would allow the warm sector of the system to cover most of the mid Atlantic states with the surface LOW going up the spine of the Appalachians.  And as you can see the European model and Monday had the main   Vort max tracking very close to the  surface Low  and right over  RDU RIC   DCA   corridor.

12Z MONDAY AFTERNOON EUROPEAN MODEL valid 4/22

*
12Z MONDAY AFTERNOON EURO MODEL valid 4/23

However since then    some of the models  have been  wavering with regard to the track of the  LOW.  This is such a significant coastal Low that some of weather hobbyists/ weenies maybe lamenting the fact that this is not occurring on February 23rd-24th because is a waste of a perfectly good coastal storm.  However I need to point out that even  if this system had occurred in late January or February it would be primarily a rain event for most of the coastal areas of the middle Atlantic  and the New England  nregions.  The entire  synoptic ( large scale atmosphere features)  is   completely wrong for anything resembling a significant East Coast winter storm for the coastal areas.

That being said…  IF…IF…   this coastal Low  were track closer to the coast… it would pull the  stalled front  from the Appalachian Mts towards the eastern  coastal areas of  NC  VA  MD .  The low level winds will become North  once the Low  reached these  eastern areas …   whch means    there  would only  be widespread heavy rains with maybe a rumble or  two of thunder ….but no significant severe weather event.  You simply do not get  ANY   kind of severe weather on the  East coast  with a coastal Low on   or  just  off the coast  with  strong  Northeast winds.  The key word here is of course significant.  And this  rule  …such as it  is… does  NOT apply  to   AL   GA SC  for  southeast   NC.

This image shows the European model from early this morning and as you can see the model clearly has a complete phase between the southern closed  Upper Low and the energy coming into the Ohio Valley from the great lakes.  They had perfect phasing of the two jet streams allows the surface low to be captured  under the   large  deep closed Upper Low  and   the Low gets  pulled North into central and Western   portions of Virginia  then into Western Pennsylvania.  In fact according to the oz  WED  European… the Low   stalls Monday morning over western of Central Pennsylvania–  New York City and Boston  would bec seeing  warm temperatures and rain   while cold air is over  WVA    western MD and most of VA.

This inland solution was supported by the 0Z  EURO ENSEMBLE    and 0z GFS .

but the 6z GFS    shifted East again taking the SE  LOW  to the NC  – VA  coastal areas…  And thus removing the threat of any sort of significant widespread severe weather for  mich of  western  & central NC and most of VA.

Unfortunately the GFS flip flop again hre at midday   with the 12z  WED    run shifting the track back to the west once more.  As you can see from this link the model now shows that the two streams to phase .  This means the southern Upper Low and  its surface Low   gets   “captured”  and pulled northward up the spine of the Appalachians…  which means that most of North Carolina Virginia and Maryland stays in the warm sector as the heart of the energy comes over these areas on Sunday.  As I said before this sort of scenario    / tracks   sets the stage for significant severe weather threat for some areas.

Complicating this even further is the new one of the European which has just come out — the 12z   WED  run.  This run of the  ECMWF  Has shifted back to the east a little bit which reduces the severe weather threat.  According to the new   run  of the European..  The phasing between the two streams takes longer to develop which forces the southeastern Low at the surface to track further to the east.

When the new 12z  European ensmbles come out it will be interesting to see if ensemble   MEAN  is supportive of the operational European or whether not it holds the consistent trend of the system tracking inland .

Of course is possible that  would they end of saying a compromise solution.  That is to say the southeast surface low tracks up into Eastern North Carolina and then makes a slow look to the Eastern VA   or  southern MD coast.  This would still placed the potential for some severe weather into Eastern Virginia but the western half of the state   as well as    WVA would see mostly just heavy steady rain.

Here is the  12z  UKMET  from  todays ‘s 12z  run… again the Low tracks  Due North  because the UKMET  says   the   2  features   Phase and  th   Low gets Pulled Due  North   into  VA  then PA

It is not out of   the question that on Monday …. IF … this system is actually has deep and as powerful as some of the models are showing…  that the rain could go over snow with the mountains of north central Pennsylvania  into central and Northeast New York State.

==============================================================

2100 EDT  17 APRIL  2012 … STAR DATE   201204.17

There is increasing potential for a significant or major severe weather outbreak for much of the southeast and lower Middle Atlantic states this coming weekend. (GA SC NC VA MD eastern TN and WVA) .  Inn addition there will be   widespread  1 to 3 inch rains from  GA  to Maine   4/22 to 4/24

So far this SPRING 2012 we have been pretty lucky on the East Coast but does not look like that Luck is going to last.

Starting at the end of this week the jet stream over the eastern portion of North America is going to undergo a major amplification.    A deep trough in the jet stream is going to form over the eastern Pacific Ocean on Thursday and Friday. This in turn… will force a large  ridge to form over the West Coast and the Rockies…    which   in turn will force large deep trough to form over the East coast this coming weekend.
*
At the surface this will appear as the cold front which will move through the Midwest on Friday and head towards East Coast. However because of this deep trough that will building over the East Coast…the cold front will come to a screeching halt along the East Coast running on a line from Atlanta to Albany NY.
*
Low pressure is going to form over AL and GA on Saturday and track up the Appalachian Mts along the stalled cold front and head into eastern PA eastern NY State and New England by Monday.  In some ways this Low track will be similar to what we might see during the wintertime with regard to East Coast winter storm. But there are some important differences.
*
FIRST… ahead of this cold front is going to turn very warm again up and down the East Coast.
SECOND… HIGH pressure off the East Coast will be sending in strong southerly winds which will increase the low level moisture from SC to Maine ahead of the cold front.
THIRD.. The pattern that sets up in the jet stream at the upper levels of the atmosphere will become very ominous looking for the East Coast and especially for GA to MD. The Jetstream over the East Coast will take on a particular tilt or alignment in the atmosphere which meteorologists call a negative tilt -- this is when the trough axis is aligned in a NW to SE direction.
*
Thus when the surface area of LOW pressure forms over GA on Saturday it will rapidly intensified as it tracks over Raliegh and central NC and into central VA/ metro Richmond area on Sunday. Because of the temperature contrast west of the front vs. east of the front… the low level southeasterly winds… the upper level south winds that will become Easterly as the Low tracks through NC and VA the potential exists for significant severe weather outbreak from Georgia into New England.
*
These two LINKS can show you the threat nicely
*
12Z MONDAY AFTERNOON EUROPEAN MODEL valid 4/22

*
12Z MONDAY AFTERNOON EURO MODEL valid 4/23

*

The thunderstorms will not only be significant rain producers but the potential exists for   Tornadic  thunderstorms as well as large HAIL.    Over the next two days I will be issuing statements on this as we get closer and closer to the event.   Most areas up and down the East Coast will see anywhere from 1 to 4 inches of rain BUT … over the mountains blue rudge and the Shenandoah Valley as well as Western NC western MD and central and northeastern PA rainfall amounts could be significantly higher.
*
Here is the approximate sequence of events for this weekend starting on Friday.
*
FRIDAY 4/20. Everybody looks fine. The looks warm and sunny the coal fund will be sweeping through the delta and the Ohio Valley. There’ wil be increasing showers and thunderstorms developing Friday night into Saturday morning over AL GA eastern TN.

SATURDAY 4/21 storms/ rain over GA SC eastern TN and western NC but it will stay dry and even sunny over eastern half NC most fo VA MD DE eastern PA.

SAT NIGHT: Heavy storms /rains move north in western VA by 8pm into western MD central PA… and into all of eastern NC VA central MD by 2am Sunday and into MD eastern PA and NJ as well as NYC

SUNDAY morning the Upper and surface Low right travel right over Raliegh and through central VA / Richmond. SEVERE WX THREAT could be HIGH for all of northern half NC – VA-MD with heavy rain. More heavy rains all for central and eastern PA NJ DE eastern NY Moderate rains into New England … by 2pm LOW is right over Richmond VA… not good

SUNDAY 7PM… the surface LOW begins to Weaken as it moves into eastern MD and towards Philly … worst is over for NC MD VA ..still some rain over nw VA and western MD and western PA… heavy rains in the NE ;

MONDAY 7AM Low is over Philly Squall line of severe storms driving thru NJ NYC se NY Long island into CT

2015  EDT  2 APRIL 2012

After record shattering warm March 2012 the pattern has shifted into something that winter lovers would love to see during the cold season months. APRIL 2012 is not going to be any where NEAR as warm as February and March was.     Late last week I issued a statement over on the Facebook page about the possibility of significant coastal storm for some portion of the East Coast during the Easter weekend.    That possibility still there but the data appears to be turning away from the big solution into smaller event

IMAGE #1 is a depiction of the current hemispheric pattern and I am using the initialization of the European on this Monday afternoon April 2. We have a very clearly defined  and easily discernible 4 wave pattern which has set up across the northern hemisphere with four large distinct Vortexes across northern hemisphere. I have highlighted these features  to  assist   in pointing pointing out   these  4  powerful large vortexes at 500 MB.:
Eastern Siberia… the Gulf Alaska ….southeastern Canada …and Scandinavia in Europe.

This is a very different pattern from what the atmosphere has been depicting over the past 4 or 5 months. More importantly…   a 4 wave pattern is very stable and is likely to stay in place for prolonged period of time. This is especially true with the NAO moving into the negative phase and possibly the AO ( arctic oscillation ) moving into the negative phase as well.

IMAGE #2 is the 12z Monday April European model valid for 72 hours ( 12z APRIL 5).    Again there are several noticeable features here.    First we can clearly see that the north Atlantic “THUMB RIDGE ” has now extended all the way into southern Greenland.    Parenthetically this has always been a point of contention with some uninformed and meteorologists and weather hobbyists: they seem to be fixated on the fact that every single Ridge n the north Atlantic is an automatic -NAO. A few weeks ago I got into a debate with some weenie on the FB page who tried to argue that having a strong ridge in the north Atlantic at 500 MB was a -NAO … and the fact that there was a huge closed deep 500 mb Low centered over Greenland did NOT count. Oh well.

But I digress. We can see a very important closed upper Low moving through the central Plains and the Lower Mississippi Valley.   This feature is part of the trough which is now over the Rockies and it is going to separate itself from the main flow on Tuesday and Wednesday.   However the number of large and powerful systems coming in across the northern Pacific into the West Coast North America shows no signs of letting up.   I have highlighted  two  important troughs in the Jet streams moving across the northern Pacific towards the West Coast.     In response to the deep and persistent   trough   over the West Coast the atmosphere is countering this feature by developing a strong Ridge over the eastern Rockies and western Plains which extends all way up into South Central Canada. This Ridge is VERY important…. because it does a number of important things…

FIRST …. these huge trough coming into the West Coast are being diverted into Western Canada and the northern Rockies which means that the upper Plains … the Upper Miss valley and south central Canada — Manitoba and eastern Saskatchewan areas  are  not getting the needed  moisture that those area needs   we move   into the heart of the Spring season.     SECOND…  the combination of the huge Ridge over the Rockies and Plains … with the -NAO over Greenland…. strongly favors a persistent and possibly a deep trough over the eastern Conus    (probably over the East Coast ).    This in turn favors below normal temperatures EAST of  the Mississippi River as long as is pattern holds. This sort of pattern is strongly supported by the Current MJO.

IMAGE #3 shows the latest European MJO forecast plots the European ensemble MJO forecast and the Ukmet forecast Plots.   As you can see over the next 7 to 10 days the data shows the current MJO will pick up in intensity then move through phase 8 and into Phase 1.   During the month of April the MJO in Phase 8 and 1 strongly supports a persistent trough over the East coast of the CONUS.

IMAGE #4 shows the 12z European model valid for 96 hours.    Note that the Upper Low that was over KS and KS has tracked ESE or SE towards the se US coast.   This is significantly different from what the model data was showing late last week;    The European model was taking this Upper Low due east to VA-NC. and  this sort of track WOULD  have  supported a significant phasing between the Upper Low in NC / VA and  the Huge Upper Low over southeast Canada..   and hence the Coastal Low.     However if the  APRIL 2 European models are correct …  the system dives of southeast  and  the potential for a significant coastal Low is much reduced. The track of the upper Low to the SE tells us that the overall   pattern  along the East Coast is not favorable for phasing but instead is favorable for suppression.     The model  produces    a coastal low off the SC- GA  Coast which would impact places such as the Masters golf tournament in Augusta.    But the coastal Low in this set up would move ENE out to sea.     April 6 and 7 would be cold — relatively speaking –with large HIGH pressure covering most of the East Coast.

But in addition …we also have that next strong system coming out of the west coast and tracking northeast into the northern Rockies ( see the “X” spot on the MAP in Image #4).   This piece of energy ( a ” short wave”)   is about to develop a   “negative tilt  ”    and this allows for the surface  Low to develop rapidly  and pull  in cold air from southwest Canada …and producing snow over Eastern MT     and  possibly the western Dakotas  on APRIL 6-7.

IMAGE #5  … shows the 12z European Model valid at 120 hrs .   The intensifying LOW  over the western Dakotas can clearly be seen — which I have highlighted in a white circle.   The Sunday GFS model runs were also quite bullish on this feature and developed a significant late season snowstorm for the western Dakotas into southern and central Manitoba APRIL 6-7.    Meanwhile over the eastern CONUS… we can see the Low way off the southeast coast and heading out to sea .

IMAGE #6 shows the day 8   ( 192 hr)   12z April 2 European model. That piece of energy which may or may not bring a snowstorm too the western Dakotas  and Manitoba …   ends up going  over the top of that huge Ridge in the Rockies and Plains …then drops southeast  into the deep trough over the East Coast.    At the surface the amplification of this trough causes a large cold HIGH to form and come south over ND… and strong surface cold front driving rapidly through the central Plains …the lower Midwest ….and into the Middle Atlantic states.    The model even develops a wave of Low pressure on the front across Central Virginia.    As you can see the dark purples and blues over south central Canada -which represents very cold temperatures for early April — is being driven southward on strong northerly winds.

IMAGE # 7 show the day 10 European with a very impressive colder outbreak which given the fact that it’s mid April… could really be called an ” arctic” outbreak.      If this map turns out to be correct we would see a hard frost and freeze across all of the Midwest east the Mississippi River and there would be significant damage to many of the vineyards across North Carolina Virginia West Virginia Maryland Pennsylvania and Western New York.

IMAGE #8 shows the 6-10 day 850 temperature anomalies…. Now we need to check the operational European because as impressive as it is the European ensemble might show something significantly different.

IMAGE # 9 is a comparison of the European Ensemble vs the operational.     In the general maps are somewhat similar but as you can see the trough over the eastern CONUS is much less amplified and therefore would not pose a threat for saying significant cold over the East Coast APRIL 10-11-12.

What happens after APRIL 11-12…. is somewhat uncertain.   If you notice the MJO forecast plots back in image #3… the Model forecast plots clearly shows the impulse collapsing rapidly in phase 1 and moving into the neutral or circle of death zone in the middle of the chart/ diagram.   This sort of development would mean that more uncertainty and shift to a pattern of persistence.