7:18 AM

Another disturbance is dropping south through the Hudson Valley, Connecticut, and Long Island Sound this morning with a round of heavy rain this morning.  This disturbance will continue to drop south and east and will exit the forecast area over the next 2 to 3 hours, impacting much of Connecticut and Long Island rush hour traffic.  Behind this disturbance is yet another mid level disturbance that is producing showers and thunderstorms over the eastern Great Lakes, which will like impact the forecast area later this evening.  The good news is that clear to partly cloudy skies can be expected through the late morning and afternoon hours for much of the region.  A few scattered showers and thunderstorms will have the potential to develop in the afternoon over the Delaware River Valley due to the sun warming the lower levels of the atmosphere, which will produce instability.  

The disturbance over the Great Lakes will approach the forecast area this evening with another round of showers and thunderstorms overnight and into Tuesday morning.  These showers and thunderstorms will be capable of heavy downpours and reduce visibility significantly, which will have an impact on the morning rush hour on Tuesday morning.  High pressure over the Great Lakes will move towards New England by Tuesday afternoon, producing partly cloudy skies and an easterly wind by the afternoon.  Although temperatures will average below normal, generally dry conditions can be expected Tuesday afternoon through much of Wednesday as high pressure will suppress any precipitation.  However, the easterly flow will support the development of fog and low clouds off the Atlantic along the coastal plain, which may lead to overcast skies and reduced visibility through the morning hours on Wednesday.  

This morning’s water vapor gives us an excellent view of the overall pattern going forward through the week.  The jet stream, in yellow, basically remains over much of the Mid Atlantic.  A deep trough over the southern Plans and West will continue to send disturbances through the Mid West and towards the Mid Atlantic through the week.  The trough over the Great Lakes suppresses the ridge over the Southeast and therefore forces the low pressure systems to move through the northern Mid Atlantic and Northeast.  However, the ridge over the Southeast and Gulf Coast prevents cold fronts to move through the region, thus causing the cold front to stall, which leads to the above normal rainfall and generally cool conditions that has been seen so far this June.  There is potential for much of the forecast area never to break 90 degrees through June as there appears to be no significant disturbance that will break the overall evolution of this pattern.  

The trough over the Northeast will temporarily lift into the Canadian Maritime through the end of the week.  With the trough exiting, a strong disturbance over the Plains will be able to drive towards the central Great Lakes and central Ontario through the end of the week.  As a result, the stationary front that has been south of the region up through Wednesday, will be forced northward as a warm front.  The upper disturbance over the Great Lakes will eventually stall over Ontario, which means that the surface fronts will slow down and stall.  Given the marine air mass in place, I don’t think the warm front will move quickly in the first place, and with weakening upper level support, the prospects of this warm front exiting quickly is even less.  As a result, I expect variable cloud cover and a threat of scattered to wide spread showers and thunderstorms Wednesday night through Friday.  A cold front will attempt to move through the forecast area on Saturday and Sunday, but will stall once again over or just west of the forecast area, producing variable cloud cover and a threat of showers and thunderstorms, potentially severe, through next weekend as well.  Overall, what will transpire is a pattern reload with a similar upper level set up reestablished by the end of the week through next weekend.

8:36 AM

Through this up coming week, the weather conditions will mirror more of late September rather than mid June as high pressure positions itself over Maine and several waves of low pressure passes to the south.  Conditions like yesterday’s heavy rain event may develop for any particular afternoon where some clearing develops and mesoscale boundaries can form, especially where lifting is possible in the upper levels of the atmosphere.  

For today, the forecast area will be on the back side of an exiting short wave trough.  The same short wave trough that enhanced lifting over the forecast area yesterday will produce subsidence or sinking air over the forecast area today.  This means high pressure will be supported over much of the region.  The sinking air over the forecast area, seen as black and red on the water vapor this morning, will suppress any mesoscale boundaries to promote wide spread rainfall.  However, I still can’t rule out a few isolated showers developing in the afternoon.  The low clouds will break up by this afternoon and will the sun’s ability to warm the lower layers of the atmosphere should not be underestimated to produce some slight instability, thus the potential for an isolated shower through this evening.  Otherwise, temperatures will average near normal with slightly lower humidity.

Through this coming week, the high pressure system over the Ohio Valley this morning will move towards Maine and the Canadian Maritimes.  The position of the high pressure system will be a key feature through the week, as the high pressure system will support a sustained easterly flow over the lower levels of the atmosphere.  This low level wind pattern will provide support for the marine air mass over the Atlantic to remain over the forecast area through the week.  Meanwhile, the stationary front will remain just south of the forecast area as weak waves of low pressure pass to the south.  The overall theme this week will be dry conditions over the Hudson Valley and much of Connecticut, however the further south one goes, the more likely they will see rain and a good dose of rain at that.  

The other issue through the week will be the potential for fog and drizzle each morning, which is usually a characteristic of marine air mass in the summer.  There will be some mornings this week were dense fog will significantly inhibit travel over much of the major interstates along the coast.  

Finally, with this type of marine air mass in place, there will be plenty of low level moisture and similar sets up to what we saw yesterday.  In locations where the low clouds break up, likely over eastern Pennsylvania and much of the Delaware River Valley, the sun will heat the lower levels of the atmosphere and produce a strong thermal gradient.  The thermal gradient could be as strong as 10° F, much like yesterday were temperatures over New York City was in the 60′s and lower 70′s while locations over eastern Pennsylvania were in the upper 70′s to mid 80′s.  If favorable upper level conditions set up to support a favorable environment for lifting, then another round of heavy rain can develop in the afternoon hours, likely after 2 PM on those afternoons.  I will have to monitor that potential each day.  

A strong occluded front will approach the forecast area by Friday and Saturday as a deep trough moves towards the Great Lakes.  This strong trough is going to reload this pattern once again, however before that can happen the trough will have to lift through the Great Lakes and the St. Lawrence River Valley.  As a result, the cold/occluded front will move through the region with periods of heavy rain on Friday evening and potentially through all of next weekend.  I think there is significant potential for this frontal structure whether occluded or cold, to slow down or stall, which would lead to flash flooding throughout the forecast area given the warm and humid air mass ahead of this front.  

It should be noted, this is a pattern that is perfect for breaking the southern New Jersey drought.  Rainfall amounts for this month are already above normal throughout the forecast area, and there are still over 16 days left in June with plenty more rainfall chances for the region.

8:46 PM

This morning I was preparing for an active afternoon of severe weather for the Delaware River Valley and eastern Pennsylvania with the potential for strong thunderstorms for the rest of the region.  While thunderstorms did organize and push towards severe levels over much of eastern Pennsylvania, the thunderstorms weakened as they moved towards New Jersey.  The strongest thunderstorms have been and continue to be located over Maryland, Delaware, and eastern Virginia.  So what prevented the thunderstorms from entering New Jersey and points east?

In the morning discussions and at the start of the “twitter” updates, I discussed that the clearing of low clouds that were present this morning along the coastal plain was going to be key in determining if severe weather would develop.  As the morning storms continued to press into the Atlantic, low clouds and showers continued to linger behind the exiting warm front.  This was due to the stubburn marine air mass hanging around at the surface through 950 MB.  As a result, clouds were slow to clear and the atmosphere did not destabilize to the full potential that was present.  However, over much of eastern Pennsylvania, the skies cleared, the temperatures jumped into the mid 70′s to mid 80′s for afternoon highs, and the atmosphere become unstable.  The result, strong to severe thunderstorms.  So in short, the fact that the strong thunderstorms, which produced very heavy rainfall by the way, moved through the coastal plain basically limited the potential for strong thunderstorms in the afternoon.  

Most locations will get a break from the precipitation tomorrow as weak high pressure ridges into the forecast area from the Great Lakes.  The cold front will stall south of New Jersey, however a few showers will still be a threat in the afternoon hours.  A strong low pressure will drive towards the Great Lakes on Wednesday night and Thursday.  As a result, a warm front will drive north on late Wednesday night with a few showers followed by a strong cold front on Thursday with the potential for strong to severe thunderstorms once again.  The set up appears to be very similar to what transpired today with the potential for severe weather influenced by the speed of the warm front and ability for the atmosphere to destabilize.  

There will remain a threat for showers and thunderstorms through next weekend as the cold front stalls south of the forecast area.  The highest threat for showers and thunderstorms will be over southern New Jersey through this weekend and there is potential for most locations to remain dry with high pressure not far away over western and northern New York.

7:18 AM

There’s a lot to discuss this morning, so lets dive right into it!

An impressive line of thunderstorms has developed early this morning in response to the strong low level jet stream at 950 and 850 MB this morning.  The warm front continues to lift north and eastward, but is having some difficulty doing so along the coast.  The thunderstorms have already reached severe levels over many locations across eastern Pennsylvania.  As these thunderstorms progress eastward, I expect the thunderstorms to become elevated.  This means the thunderstorms will be forced to move over the relatively cooler air mass along the New Jersey coast and much of the New York City metro including Connecticut.  The thunderstorms as a result will weaken slightly but will continue to produce heavy downpours, strong wind gusts exceeding 45 mph, and frequent lightning.  However, this round of showers and thunderstorms is only the first round of potential severe weather for the region.  

There are several important features to note on this morning’s surface map, provided by the SPC.  The warm front, which is still east of the forecast area basically is situated from eastern Virginia through central Maryland, and east-central Pennsylvania this morning.  There is a push of warm, moist air directly behind the warm front which is driving the thunderstorms this morning.  An easterly fetch ahead of the warm front along the New Jersey coast is supporting an environment for dense fog and low clouds, which is also stabilizing the atmosphere.  This is an important to key to the forecast going forward!  Meanwhile, the cold front is still located over central Ohio.  

The question for the forecasting of severe weather this afternoon is just how much clearing will develop this afternoon ahead of the cold front .  Also, there is now a question of just how far north and east the warm front will get before an occlusion develops and limits severe thunderstorm potential.  Currently, my thoughts is that the warm front will have a difficult time getting east of the immediate New Jersey coast, New York City, Long Island, and much of Connecticut.  These locations will have a period of heavy rainfall and thunderstorms through the early afternoon hours, followed by a break, and another round of showers and possibly thunderstorms in the very early evening before drying out completely.  The stable nature of the low level atmosphere will limit the development of thunderstorms and weaken any convective precipitation that enters the region.  However, a much more complicated forecast can be found over eastern Pennsylvania and much of the Delaware River Valley.  This location includes much of the Philadelphia metro and interior central, southern New Jersey.  The warm front will move north and east of these locations later this morning and some clearing will take place, which will allow the June sun to do some dirty work.  Temperatures will spike into the upper 70′s to lower 80′s, which will significantly destabilize the atmosphere.  The low level lapse rate will likely jump into the the 6 to 7.5 C/km range, which will support the development of strong to severe thunderstorms later this afternoon as the cold front approaches.  Winds shear will be a factor to deal with as well as I expect weak directional wind shear between 850 and 500 MB, which is a mid level wind shear component and will support the development of weak mesoscale lows within the thunderstorms.  Meanwhile, the strong 850 MB low level jet stream will interact with the stronger upper level winds at 500 MB to produce some speed shear as well.  Combine these factors with plenty of ample moisture and strong PVA from the approaching trough, and the ingredients do come together nicely for the potential for severe weather.  

One additional aspect to keep an eye on is seen on the water vapor image this morning.  Note the black colors over the Great Lakes and Ohio Valley this morning.  This is an area of cool, dry, sinking air that is right behind this cold front.  This area of cooler air can be found at 500 MB and is actually extending further east over the developing convection over the Ohio Valley.  This cooler air with support a significant destabilization of the air mass over much of Pennsylvania and could extend into western New Jersey.  If this does happen, then the potential for large hail and very strong downburst wind gusts will increase over the forecast area.  Sometime to keep an eye on through this afternoon.

The cold front will stall over southern New Jersey on by Wednesday morning with weak waves of low pressure passing to the south of the region, which will bring a threat for a few isolated showers.  However, most locations will remain dry with partly cloudy skies.  Another low pressure system currently organizing over the central Plains will race towards the eastern Great Lakes on Thursday.  The low pressure system will force the stationary front north and eastward on Wednesday night and early Thursday morning.  The cold front will follow on Thursday afternoon with a near similar set up to what is being seen this morning.  Another round of strong to severe thunderstorms will be possible through early Thursday afternoon before the cold front exits off the coast.

High pressure from the Great Lakes will briefly build into the region on Friday and Saturday with clear skies and near normal temperatures.  However, another slow moving low pressure system will impact the forecast area on Sunday afternoon through Monday morning with showers and thunderstorms once again.  The active pattern is expected to continue through next week as well with temperatures averaging near normal.

7:40 AM

The latest visible satellite image clearly shows that fog has developed throughout much of the forecast area with dense fog advisories issued for much of the region.  The dense fog has developed due to a combination of lingering low level moisture from a few showers early this morning and very light winds.  The good news is that the fog will burn off my later this morning giving way to a great Spring afternoon with mostly clear skies, light southeasterly winds, and temperatures rising into the upper 50′s along the immediate coast to mid 60′s over the rest of the forecast area.  

However, trough is not far behind as a strong disturbance seen on the water vapor satellite image over the southern Plains, begins to develop rapidly.  Note several features on the satellite image to the left.  First, a strong yet small disturbance is diving into western Texas this morning and is already pulling up a great deal of moisture from the Pacific and from the Gulf of Mexico.  Also note that the cold front boundary that moves through yesterday has stalled over the Southeast with a great deal of moisture pooling along the Gulf Coast.  While the forecast area is caught in between these two areas of moisture at the mid levels, which will produce a very nice afternoon today, the disturbance and the moisture over the Southeast will interact to produce a very active weather day on Friday.  

The surface low pressure system with this upper low is expected to develop rapidly and drive towards the eastern Great Lakes by tomorrow afternoon.  Given the position of the upper level trough and the development of the strong PVA within the trough, the environment is very similar to what was seen on last Sunday.  

The actual timing of when and what type of precipitation (steady rain or severe thunderstorms) is going to strongly depend on the development and position of the warm front on Friday afternoon.  Note the surface map to the left.  

On Friday afternoon, the upper low at 850 MB will be positioned over Lake Erie, which will put the forecast area in an area where winds are backing from south to southeast depending on location.  The northern portion of the forecast area will be in a lull as far as mid level wind strength, which is important.  This means that this location will lack addition mid level forcing to support a prolonged rainfall.  As a result, while I expect a period of steady rainfall, that period may be short lived in the afternoon as the best dynamics for precipitation lifts away from the Hudson Valley and Connecticut.  The immediate New York City metro is a bit more difficult to nail down as isentropic lifting along the warm front will mean that while showers and thunderstorms (although weak) will be a threat for much of the late morning to late afternoon hours.  South of the warm front is where the weather is going to get pretty interesting.  The warm front is only going to get as far north as central New Jersey or just about to Trenton, New Jersey before being pushed east and off the coast.  The locations to the south of this warm front will see a volatile change in conditions and temperatures through the afternoon once the warm front pushes north.  Based on the soundings over these locations, I expect the overcast conditions expected in the morning to break up.  The more sun that is present, the more unstable the atmosphere will become over the lower and mid levels.  Temperatures will quickly spike from the 50′s into the mid to possibly upper 60′s, especially over southwestern New Jersey and the Philadelphia metro.  Areas within the dashed line, which is basically 5 to 10 miles away from the immediate coast line, are where I expect temperatures to spike and the atmosphere to become the most unstable.  Of course the one uncertain part of this forecast is how the dry low level boundary layer over Southwestern New Jersey will have an impact on thunderstorm development.  At this time, this feature is a wild card.  It may be a non-factor, but the dry low level may inhibit the full potential of thunderstorm development.  

The main threat from the thunderstorms tomorrow afternoon will be very strong wind gusts as the thunderstorms are expected to be of the low-top variety.  As the thunderstorms lift north of the warm front towards New York City, the thunderstorms will be elevated which may bring a risk of small hail into the New York City metro.  The occluded front will clear the forecast area by Friday evening with clearing skies overnight.  

The strong low pressure system will lift into New England and eastern Canada on Saturday.  While dry conditions are expected for the majority of the forecast area, except for the central Hudson Valley and Connecticut where a stray shower may pass through in the afternoon, very windy conditions will be the main story on Saturday.  The tight pressure gradient that is generated primarily from the exiting low pressure system will produce a west to northwesterly wind around 15 to 30 mph.  The good news is that temperatures will remain near normal with highs in the lower 50′s to lower 60′s.  

High pressure will build into the forecast area on Sunday with clear skies, lighter winds, and temperatures near to slightly above normal.