04/27/10  7:07 AM

The upper low responsible for the bouts of heavy rain and overcast conditions the past two days is finally exiting into the Atlantic.  Note the strong disturbance on the water vapor over the Mississippi Valley.  That disturbance is called a “kicker” in the meteorology world because that disturbance will kick the coastal low east of New Jersey into the Atlantic.

So after a few lingering showers this morning and overcast skies, dry air will work in from the west, which will lead to clearing skies by this afternoon.  The disturbance over the Mississippi Valley will remain well south of the northern Mid Atlantic tonight, exiting into the Atlantic.  However, as the “kicker” disturbance moves into the Atlantic tomorrow morning, the coastal low (that’s exiting off the New Jersey coast this morning) will interact with the “kicker” disturbance and intensify.  As the coastal low intensifies, the pressure gradient over New England and the northern Mid Atlantic will increase, leading to rather windy conditions through the day on Wednesday.  Winds will be sustained from the northwest around 10 to 20 mph with gusts to 25 to 30 mph at times.  While no precipitation is expected, the windy conditions will make high temperatures in the 60′s feel like the 50′s.

As the coastal storm finally pulls into the Canadian Maritimes on Thursday afternoon, a significant change in the pattern will take place!  Over the past several weeks, a strong upper low has been sitting to the east of Maine, leading to a persistent influence of marine air masses, slow moving low pressure systems, and temperatures averaging near to slightly below normal. By the end of this week, that upper low (which is associated with the negative NAO pattern) will shift north and east, and that change is extremely important.

Note the 500 MB map to the right via the 00Z GFS.  Because the upper low over the Canadian Maritimes is further north, the ridge is able to build into the St. Lawrence River Valley.  This leads to a southwesterly flow aloft and at the surface, which means much warmer times ahead for the northern Mid Atlantic as a while.  This type of pattern also leads to cold fronts attempting to run right into the ridge and weaken as they do so, which leads to widely scattered but at times very impressive strong to severe thunderstorms in the afternoon and evening hours.

So after Thursday, expect a significant moderation in the high temperatures for Friday through Monday with highs in the 70′s and 80′s for much of the northern Mid Atlantic.  Each afternoon and evening will feature a threat for thunderstorms, but not a wash out as most of the region will remain dry, warm, and humid!  Welcome to a taste of summer!

For a detailed seven day forecast, go here!

04/26/10  3:37 PM

The rain is almost near an end, but another round will have to move through before much more pleasant conditions return to the Philadelphia and New York City metropolitan areas.

The upper low that has been sitting over the Ohio Valley is finally moving east towards the Mid Atlantic coast.  The area of rain over southern New York through Connecticut and south through the Delaware River Valley is associated with an upper level occluded front and upper level cold front.  A break in the rainfall is located over central Pennsylvania, associated with sinking air as a response to all the rising air to the northeast.

The scattered showers and thunderstorms over southwestern Pennsylvania, Maryland, and Virginia area associated with the upper low itself.  The showers and thunderstorms with the upper low will have the potential to produce very heavy downpours, hail, and frequent lightning; however be the time the upper low reaches southern New Jersey early tomorrow morning, the air mass will be much more stable with less of a threat for strong thunderstorms.

For this evening, periods of steady rain can be expected, especially over the Hudson Valley and Connecticut.  There is a chance for a prolonged break in the rainfall over much of New Jersey through Long Island this evening as the area of sinking air drives east.  So those going to the Citi tonight have a shot at some improving conditions after some steady rain through 7, possibly 8 PM.

The upper low will move off the coast of New Jersey tomorrow morning with lingering rain showers continuing through the morning hours.  The low pressure system will finally exit by Tuesday afternoon with clearing skies and winds backing to the northwest.

As the low pressure system exits, the upper low will interact with a Polar disturbance and cause the storm to explode over the Canadian Maritimes.  While conditions will be dry for the most part on Tuesday evening through Wednesday, windy conditions can be expected as well with gusts over 35 mph possible along the coast.

A distinct pattern change will take place by mid week as an upper level ridge builds over the Eastern United States.  As high pressure shifts off the Southeast coast, a southwesterly flow will become established.  A trend to much warmer conditions will take hold with high temperatures in the 70′s and 80′s by the end of this week.

By the weekend, the warm and humid air mass will be established over the northern Mid Atlantic, however mid level disturbances over the Tennessee Valley will lead to a threat of widely scattered strong to severe thunderstorms each afternoon for next weekend.

For a detailed break down of the next seven days, go here!

04/26/10  7:27 AM

An area of low pressure over Ohio will slowly move to the east today with another round of moderate to heavy rainfall later this morning through early this evening.  The rain will be heavy at times with another half inch to an inch of rain possible by late tonight.

As the area of low pressure moves off the New Jersey coast tonight, the rain will intensify once again along the immediate coast.  The rain will continue on through Tuesday morning but will taper off towards noon tomorrow.

So, basically we have another 24 to 30 hours of overcast skies, patchy fog, and periods of moderate to heavy rain to contend with to start the week.  Temperatures won’t move much from the 40′s and 50′s as well, but the apparent temperatures will feel like the 40′s under these gloomy conditions.  However, there is some good news!

Once this storm exits, a new pattern will take hold and one that will be very pleasant for many throughout the Philadelphia and New York City metropolitan area!  A strong upper low over eastern Quebec will continue to shift east towards the Canadian Maritimes on Tuesday night and Wednesday, which will put the region in an area of convergence and confluence.  This type of pattern supports high pressure over the Tennessee Valley to intensify, which will provide a cool yet dry northwesterly flow over the region through mid week.  Temperatures will average near normal with highs in the 60′s and lows in the 30′s (mostly over the interior) and 40′s.  Then the real change in the pattern takes hold!

The pattern over the past several weeks has been what we call in the meteorology world, a west based negative North Atlantic Oscillation pattern.  This type of pattern keeps a marine influence throughout the Northeast and Mid Atlantic along with a constant threat for slow moving low pressure systems and rain.  However, the negative NAO will shift to the east or become east bases.  This shift is extremely important as the upper level pattern takes a big shift to the east.  This brings a ridge into the East coast, and trust me, we like ridges in the Spring and Summer!

On Thursday and Friday, the upper level ridge will build from the Ohio Valley towards the East coast with the ridge axis moving right over the northern Mid Atlantic on Friday evening.  High pressure at the surface will set up off the Southeast coast, producing an increasingly strong southwesterly flow, which will support impressive warm air advection throughout the northern Mid Atlantic.  Temperatures will warm into the 70′s for highs as a result while humidity will also be on the increase.

By Saturday and Sunday, the ridge axis will be to the east of the region at 500 MB.  This will produce a southwesterly flow at all levels of the atmosphere, but also start to introduce the influence of disturbances approaching from the southwest and moving northeast.  Given the blocking nature in the pattern, this ridge is not going to give way all that much from Saturday on to early next week, which means any cold front that approaches will stall or weaken rapidly while approaching.  We saw this last Spring and Summer as well.  This type of pattern introduces plenty of warm, moist, unstable air into the region ahead of strong disturbances, which spells the threat for strong to severe thunderstorms on the afternoons of Saturday and Sunday.

Now, I don’t expect organized precipitation on Saturday or Sunday so not everyone will see a storm.  However, if a storm does impact your location, it will likely be in the time period between 1 PM and 6 PM when the atmosphere becomes most unstable.

Well, to the late Spring pattern, lets see how long this will ride!

For a detailed seven day forecast, go here!

04/25/10  9:53 AM

Steady, moderate to heavy rain has moved through the New York City and Philadelphia metropolitan areas this morning as an 850 MB warm front drives north towards New England.  The problem is that the surface warm front didn’t follow.

With the surface warm front located over the Delaware Bay back through the Maryland/Pennsylvania boarder and the mid level warm front driving north, the stage is set for a persistent isentropic lifting environment.  What does this mean for you and me?

Well, with a stiff easterly wind transporting plenty of moisture from the Atlantic into the northern Mid Atlantic at the lower levels, overcast skies, drizzle, and scattered showers can be expected through this evening in place of the strong lifting from the mid level warm front this morning.  So, the region will get a break in the steady, heavy rain by this afternoon.  However, weather conditions will just be plain raw outside.

This morning’s water vapor shows us the culprit behind all this rather miserable weather as a strong upper low over the Mid West tries to run up against an even stronger upper low over the Canadian Maritimes.  In the end, the negative NAO supported upper low over the Canadian Maritimes is going to win out, forcing the upper low over the Mid West due east towards the Mid Atlantic coast by Tuesday morning.  What this means for the region is a persistent southwesterly flow from the Gulf of Mexico into the Mid Atlantic.  The conditions in place now, will remain through tonight.  However, with additional lifting from the approaching upper low, rain will become more steady.  The idea behind the forecast is that each impulse from the upper low will produce another wave of more to heavy rain.  The next threat for moderate to heavy rain will be late tonight through tomorrow morning, making for a rather nasty Monday morning rush hour.  The third wave will come on Monday night through Tuesday as the surface and upper low passes over southern New Jersey and exits into the Atlantic.

Rainfall amounts through this entire forecast period will easily exceed an inch of rain, with the threat of as much as two and a half inches of rain in some isolated locations due to heavy downpours.  There is a threat for flash flooding of rivers, streams, and urban locations.  However, the rainfall from this storm will not be as impressive as seen in previous storms this early Spring.

The good news is that once this storm leaves on Tuesday night, weather conditions rapidly improve with clear skies through much of the rest of next week and rapidly modifying temperatures.  In fact, by Friday, high temperatures for many locations will likely push through the 60′s and into the lower 70′s.  However, the best is yet to come!

A change in the pattern is on the way, and with it much warmer, summer like conditions and the return of strong to severe thunderstorms each afternoon.

For a detailed look at the next seven days, go here!

04/24/10  9:00 AM

High pressure will provide another excellent weather conditions through this evening with highs in the 60′s and 70′s with only a few increasing clouds in the afternoon.  Otherwise, today is clearly the day to get out and do outdoor activities.

A warm front currently approaching the Tennessee River Valley will drive north towards the Philadelphia metropolitan area tonight.  Clouds will increase, but rain should hold off until after midnight even for southern New Jersey.  High pressure that is currently hold off the rain today will be an important factor over the next several days, as the high pressure will reinforce an impressive marine air mass over the New York City and Philadelphia metropolitan area.

Tomorrow morning through Tuesday morning, the warm front will be stalled right over southern New Jersey back through northern Delaware, and the Maryland/Pennsylvania boarder.  With the warm front attempting to drive warm, moist air over the stubborn marine layer in place, periods of moderate to heavy rain over much of the northern Mid Atlantic for several days.

The rainfall currently moving into southwestern Pennsylvania and northern Virginia will become enhanced by the clash of air masses, which leads to what is called isentropic lifting.  Basically, warm moist air is being forced over the cool, marine air mass in place.  This leads to strong lifting and thus the heavy rain.  So, tomorrow through Tuesday expect overcast skies, periods of moderate to heavy rain, and a stiff east to northeasterly wind over the next several days.  In short, raw and ugly!

The area of low pressure associated with this warm front will eventually move off the New Jersey coast by Tuesday morning with another round of moderate to heavy rain through early Tuesday afternoon.  The rain will exit by Tuesday evening and what will follow will be enjoyed by many.

High pressure will dominate Wednesday through Saturday with gradual moderating conditions.  Temperatures through the end of next week will average near normal with 60′s and 70′s for highs, however by Saturday summer returns.  High temperatures on Saturday are expected to drive into the 70′s and even 80′s with a distinct change to the pattern on the way.  Summer like conditions are on the way.

For a detailed look at the next seven days, go here!