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
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
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