7:30 AM

The forecast for today through tonight is best described as significantly complicated and potentially very active.  The main theme is basically the progression of the warm front currently over southwesterly Pennsylvania through eastern Virginia.  I want to start with the fact that the surface low pressure system is further north and weaker than forecasted on any model guidance to this point.  The cold front is actually well to the west and will eventually become nothing more than a boundary between the very moist air that will move into the forecast area and the drier air that will eventually build in.  However, before I get to all of that, let’s discuss the events for this morning.

The majority of the showers and thunderstorms over western and central Pennsylvania have been weakening this morning due to the weakening of the low level jet stream at 850 MB.  The upper level winds this morning are also from the northwest throughout the Mid Atlantic, which is forcing much of the precipitation south and southeast thus slowing the progression of the heavy precipitation eastward this morning.  However, eventually the low pressure over the Great Lakes will move north and east into the eastern Great Lakes and St. Lawrence Valley this afternoon, which will drive the warm front through the forecast area this afternoon.  As the warm front moves north and east, showers and thunderstorms will redevelop throughout the region.  The showers and thunderstorms ahead of the warm front will be able to produce very heavy downpours. 

Note the surface map above.  Dry, cool air is in place over much of the New York City metro down through the northern suburbs of Philadelphia.  This dry, cool air will be slow to leave the forecast area, which will increase the development of isentropic lifting this afternoon.  In other words, the cool air over the forecast area ahead of the warm front will force thunderstorms to become elevated, which will lead to very heavy downpour over the forecast area this afternoon.  However, south of the warm front, a very different environment will develop. 

South of the warm front, a very warm and unstable air mass is in place.  The map to the left shows that atmosphere is very unstable south of the warm front and wind shear increases dramatically.  I don’t believe the warm front will clear all of the forecast area, in fact much of northern New Jersey and the New York City metro will remain north of this warm front.  However, all of central and southern New Jersey including all of southeastern Pennsylvania will be under the threat of strong to severe thunderstorms as the warm front moves north.  

So here is what to expect through today.  Clouds will continue to increase through this morning ahead of the warm front.  By around 11 AM, steady rain will enter the forecast area from eastern Pennsylvania and will push eastward through the afternoon hours.  The showers and thunderstorms will eventually have a significant impact on the Mets and Phillies baseball games this afternoon and evening.  As the warm front pushes north and east, a brief break in the rainfall can be expected.  Scattered showers and strong to severe thunderstorms will develop later this afternoon behind the warm front.  These thunderstorms will be capable of wind gusts exceeding 55 mph, large hail, very heavy downpours, and even an isolated tornado.  The combination of the heavy downpours over the forecast area that has already seen rainfall amounts two to three times what is normal will lead to the potential for flash flooding throughout the forecast area.  The low pressure system will move through New Jersey later this evening and slowly exit overnight.  As the low pressure system exits, lingering showers will remain over the forecast area especially along the coast.

By tomorrow, slow clearing can be expected with overcast conditions and scattered showers throughout the forecast area.  Clouds will break up by the mid to late afternoon hours with much drier conditions by the evening hours.

A significant change in the pattern will finally unfold for next week.  The upper trough will reposition itself off the coast, which will produce a northwesterly to northerly flow over the forecast area.  The position of the trough will mean that most disturbances will remain east of the forecast area, which will mean much drier conditions for the region.  High pressure over the Ohio Valley will bring clear to partly cloudy skies and much warmer, more seasonable conditions for the forecast area.  In fact, locations over the Delaware River Valley may even reach 90 degrees for afternoon highs by mid week.  Locations along the immediate coast will have to contend with influence from the Atlantic, which may lead to overcast skies in the morning and cooler temperatures than surrounding areas inland.  A new disturbance will approach from the west on Friday as the trough retrogrades back towards the Great Lakes with scattered showers and thunderstorms.

So overall, a very active period of weather over the next 36 hours will be followed by more summer like conditions through much of next week.  Expect updates via twitter through the day!

Most recent updates on the bottom!

12:40:48 PM: The strongest thunderstorm of all the thunderstorms throughout the region is over western Burlington County.

12:42:03 PM: The thunderstorm over western Burlington County is producing very heavy rainfall and frequent lightning.

12:43:03 PM: These thunderstorms are below severe level, but can reduce visibility rapidly due to the heavy rainfall and strong wind gusts.

12:44:14 PM: A strong shower over Bergen and Essex County of New Jersey is tracking towards Bronx over the next few hours.

12:44:14 PM: A strong shower over Bergen and Essex County of New Jersey is tracking towards Bronx over the next few hours.

12:47:11 PM: Several lines of strong thunderstorms are developing over eastern Pennsylvania. The main threat from these thunderstorms is heavy rain.

12:54:24 PM: I’m becoming very concerned about flash flooding for western Burlington, Camden, and western Gloucester Counties of New Jersey.

12:58:42 PM: Doppler estimated rainfall amounts are approaching an inch and a half over western Burlington County, especially over the town of Crossroads

1:05:35 PM: A disturbance moving through NW Ohio and W PA will have an impact on the forecast area this evening with potentially strong thunderstorms.

1:05:58 PM: So the thunderstorms over the region now is due to the instability from the sun warming the lower levels.

1:06:26 PM: Meanwhile, more thunderstorms are possible due to the upper level disturbance approaching from the west this evening.

1:07:22 PM: Meanwhile, more thunderstorms are developing due to the outflow boundaries from the initial thunderstorms.

1:07:55 PM: An example of this can be seen over Bucks County as one thunderstorm is drifting to the northwest.

1:12:28 PM: So far the thunderstorms have stayed below severe levels. Given the lack of lightning so far, these storms are more like heavy showers.

1:28:57 PM: The Delaware River Valley is just being crushed by heavy rainfall right now.

1:29:25 PM: Meanwhile, the storms over the Bronx have weakened rapidly due to the marine layer in place.

1:33:06 PM: A flood warning for small streams and urban areas has been issued through 4:15 PM for Burlington County.

1:35:49 PM: The heavy rain is expanding towards Monmouth and Ocean Counties of New Jersey as the storm drift north.

1:33:06 PM: A flood warning for small streams and urban areas has been issued through 4:15 PM for Burlington County.

1:35:49 PM: The heavy rain is expanding towards Monmouth and Ocean Counties of New Jersey as the storm drift north.

1:36:30 PM: There is a weak sea breeze front over eastern Monmouth and Ocean Counties that will have to be watched.

1:36:58 PM: This boundary may produce very heavy rain for central and western Monmouth and Ocean Counties.

1:38:09 PM: Meanwhile, the thunderstorms over the southern Hudson Valley and Connecticut have basically fallen apart. This includes the Bronx.

1:40:33 PM: The nature of these thunderstorms is to move very slowly, which is why heavy rain is becoming an issue.

1:46:40 PM: A Flash Flood Warning has been issued for central Burlington County. Local law enforcement has reported roads being washed out.

1:47:20 PM: Doppler Radar estimates are now exceeding 2.5″ of rain so far from these thunderstorms.

1:51:36 PM: An impressive line of showers and thunderstorms has developed from SE to NW stretching from Ocean County, NJ to Luzerne County, PA

1:52:15 PM: These thunderstorms will continue to drift towards the northeast and east towards the coast and the New York City metro.

1:54:58 PM: Given the marine air mass along the coast, I think these storms will peak over central Sussex County down through central Monmouth County.

1:55:21 PM: Then the storms will weaken as they are elevated over the marine layer.

1:55:50 PM: Note that temperatures along and behind these storms are in the upper 70′s to lower 80′s with mid to upper 60′s for dew points.

1:56:28 PM: Ahead of these storms along the coast, temperatures are in the lower 70′s and dew points in the upper 50′s. This air is more stable.

2:17:08 PM: A perfect example of what to expect this afternoon can be found over Sussex, Morris, and Passaic Counties of New Jersey.

2:18:27 PM: As the thunderstorms moved east, they rapidly weaken to moderate showers and continue to weak as they move east. This may protect NYC.

2:33:55 PM: A severe thunderstorm has developed over New Castle, DE and will likely impact Salem County in New Jersey with nickel size hail.

2:36:23 PM: I am now convinced that the heaviest rain is going to remain from Eastern PA to west/central New Jersey, or the Delaware River Valley.

2:41:28 PM: Flash Flood Warnings are now issued for central and southern Bucks, northern Lehigh, Carbon, Northhampton, and Monroe Counties of PA.

2:55:42 PM: Very strong thunderstorm now moving through Hunterdon County of NJ right now. Still below severe level however.

2:57:08 PM: Note that as this line of storms moves NE that they continue to weaken and become elevated heavy showers.

3:08:57 PM: This evening is starting to look very interesting for E PA and W NJ as the lifting from the disturbance to the west approaches.

3:33:25 PM: A band of showers is currently moving over Yankee Stadium. These showers will likely linger through the game.

3:35:12 PM: The strong thunderstorms that were over W-C NJ have become an area of heavy rainfall slowly drifting towards New York City.

3:43:00 PM: There is a real potential for flash flooding over Middlesex, Union, Sommerset, and eastern Hunterdon Counties of New Jersey.

3:45:20 PM: Doppler estimated rainfall amounts of 1 to 3 inches are being produced by these thunderstorms, some isolated amounts to 5 inches.

3:48:53 PM: Locations from SE Montgomery through Union, NJ are receiving very heavy rainfall. A flood warning should be issued for these locations soon

3:49:43 PM: Another line of storms and strong showers is approaching from NE PA and will enhance the rain over N-C NJ this afternoon.
3:54:05 PM: As these two mesoscale boundaries interact, showers and thunderstorms will continue to develop and train over N-C New Jersey.
3:59:40 PM: For those at the Mets/Yankees game, get ready for some wet weather.

4:22:15 PM: Baseball update: Heavy rain is approaching from Essex County and should enter the Bronx in roughly 15 to 30 minutes.

4:22:15 PM: Baseball update: Heavy rain is approaching from Essex County and should enter the Bronx in roughly 15 to 30 minutes.

4:28:15 PM: Note that the DBZ over E-C New Jersey has collapse from 45 DBZ to 25 DBZ in roughly 30 minutes. This means the showers are weakening.

4:29:40 PM: Very interesting development. The boundary over Sussex, Warren, and Northhampton Counties is pushing the C-NJ boundary south.

4:30:13 PM: This MAY mean that the Bronx dodges much of the heavy rain, but I am not confident of that.

4:30:42 PM: Meanwhile, heavy rain has started to move into Monmouth County. Heavy rain is falling over Freehold right now.

4:32:32 PM: The sinking air from the northern boundary is helping to weaken the rainfall over Morris, Essex, Hudson, and Union Counties.

4:33:03 PM: The rainfall is MUCH heavier over Mercer County, NJ and Bucks County, PA.

4:51:03 PM: For those at the baseball game, showers are breaking up as the main focus of the line is pushed south towards central NJ.

4:52:00 PM: These mesoscale boundaries are acting a lot like Lake Effect snow bands in terms of movement. In a way, these seem like moisture plumes.

4:54:39 PM: The heavy rain is now focusing over Middlesex, Monmouth, and Mercer Counties of NJ and Bucks and Montgomery Counties of PA.

4:55:23 PM: Meanwhile, the disturbance well to the west is starting to produce thunderstorms over E-C PA, which are racing eastward.

4:56:03 PM: The interaction of the mesoscale boundaries and the upper level disturbance is going to complicate the forecast for this evening.

5:21:16 PM: A Flood Warning has been issued for Neshaminy Creek at Langhorne in Bucks County through 8AM Sunday.

5:45:04 PM: The upper disturbance is approaching fast with strong to severe thunderstorms developing over Wyoming County, PA and racing SE.

5:58:53 PM: Very strong thunderstorms are developing over Chester County and also starting to produce very heavy rainfall.

5:59:37 PM: I think the upper disturbance approaching from the west will enhance this heavy rainfall. I’m watching to see if the rain band moves north.

6:15:31 PM: Strong thunderstorms approaching Lackawanna and N Luzerne Counties of PA.
6:25:52 PM: A severe thunderstorm warning has been issued for S Lackawana and NE Luzerne Counties of PA for nickel size hail.
6:32:30 PM: As the sun sets, the mesoscale boundaries that have produced the heavy rain will weaken.

6:33:30 PM: However, showers and strong to severe thunderstorms will remain a threat as the upper disturbance approaches from the west.

6:44:56 PM: The severe thunderstorm warning has been extended to Monroe County of PA. This storm will also impact Warren and Sussex County.

7:02:49 PM: Scattered thunderstorms are redeveloping throughout eastern PA, however as the sun sets these storms will remain below severe levels.

7:03:13 PM: The thunderstorms however will impact the Phillies/Boston game this evening and may even cause a postponement.

8:05:07 PM: As the upper disturbance approaches, a line of strong to severe thunderstorms are driving south and east towards the forecast area.

8:06:23 PM: These thunderstorms will continue to dive south through NE PA and through much of NJ, SE PA, and much of the NYC metro.

8:07:49 PM: These thunderstorms are capable of frequent lightning, nickel to quarter size hail, and very heavy downpours.

8:08:33 PM: The heavy rain over central NJ and the Philadelphia metro has weakened considerably as the sun sets and the mesoscale boundary weakens.

8:15:00 PM: These thunderstorms will only intensify the flooding conditions that have developed throughout E PA and much of NJ.

8:15:30 PM: The good news though is that the storms are moving relatively fast and will be weakening as the evening progresses.

8:20:34 PM: The lower end of this line of thunderstorms over Schuylkill County, PA is becoming very impressive.

8:21:06 PM: This section of the line of thunderstorms should impact SE PA including Philadelphia and much of central/southern New Jersey through tonight

8:21:40 PM: The line of thunderstorms will be capable of frequent lightning, small hail, wind gusts over 50 mph, and very heavy downpours.

8:42:42 PM: As this line of thunderstorms approach, they will be lifted by the marine air mass.

8:44:04 PM: As a result very heavy rain and strong wind gusts can be expected overnight as the thunderstorms drop south and east.

4:09 PM

The majority of the showers and thunderstorms that have formed this afternoon are the direct result of the sun being allowed to warm and destabilize the lower boundary layers of the atmosphere.  Showers and thunderstorms will continue to intensify and rotate northwest to southeast through the forecast area.  However, as the evening progresses and the sun sets, the majority of these thunderstorms will weaken and/or completely dissipate throughout the forecast area.  As such, my thoughts are that by 8 PM the majority of the forecast area will have dry yet overcast conditions.  The majority of the disturbances this afternoon are focused over the Mississippi Valley and Tennessee Valley, were some significant severe weather is developing.  These disturbances will have an impact on tomorrow’s weather conditions for the forecast area and will have to be monitored, however for now the overall theme is that the game conditions should be fine for the Mets and Yankees game in the Bronx.

1:33 PM

As the cold front stalls over the New Jersey coast this afternoon, some of the low clouds have broken and has allowed the sun to break through.  As a result, the atmosphere is warming and becoming unstable.  With the frontal boundary remaining an area of focused low level lifting, this means the development of scattered showers and thunderstorms will continue to become favorable.

Already we have been seeing isolated thunderstorms beginning to develop over southern New Jersey and across the eastern half of Pennsylvania.  These thunderstorms will likely remain below severe levels as the atmosphere just is not going to support a wide spread severe event given the lack of wind shear that is present.  However, there is plenty of moisture hanging around the region and with mid level and upper level winds generally weak over the forecast area, there is potential for these thunderstorms to move slowly and to produce very heavy rainfall over localized areas.  

As for the big Mets and Yankees game in the bronx, for now the threat of showers still remains, but there is just as good of a chance that no rain falls through this evening as there is a complete wash out.  Really the state of weather conditions at the Bronx will depend on where the thunderstorms form and what direction do they move.  I will keep an eye on those factors through the day.

7:10 AM

If you go outside, you probably won’t believe that the Mets and Yankees start playing real baseball games in roughly two weeks!  A strong arctic high pressure is positioned over Quebec this morning and supporting a cold, dense air mass over the forecast area this morning.  Temperatures this morning have ranged from the lower to mid 20′s along the coast to the mid to upper 10′s over some interior locations.  Now those temperatures are a good 15 to 20 degrees below normal for many locations.

The high pressure system today will build south and will sit over the forecast area by tomorrow morning.  The strengthening March sun will marginally help to warm the cold, dense air mass with highs into the lower to mid 40′s by this afternoon.  With the high moving right over the region tonight and tomorrow morning, clear skies and light winds can be expected.  This type of environment strongly supports radiational cooling and will allow temperatures to crash once again into the mid 10′s to mid 20′s for lows throughout the forecast area.  The typical cold valley locations will cool the most like over northeastern Pennsylvania, interior Long Island, northwestern New Jersey, interior Connecticut, and the Hudson Valley.  

The upper level pattern, which has been discussed at length the past few days, will begin to weaken and break down by Wednesday night.  High pressure will move to the south and east of the forecast area, which will allow winds to veer to the south and southeast.  The weakening block will also allow the cold front that moved through on Sunday to rebound as a warm front on Thursday afternoon.  

A weak disturbance out of the Ohio Valley will move towards the forecast area on Thursday with scattered showers by Thursday afternoon.  The isentropic lifting with this low pressure system is not very impressive, nor is the upper level support so I have a hard time buying into the wide spread QPF seen on the GFS, however I do expect showers on Thursday afternoon through early Friday morning for the entire forecast area.  Temperatures by Thursday afternoon will rebound to near normal levels with highs in the upper 40′s to lower 50′s.