06/10/10  8:45 AM

The low pressure that produced the moderate to heavy rain over the Philadelphia and New York City metropolitan area is now exiting into the Atlantic.  What will follow is a rather complicated and volatile period of weather that will sure to drive the public and meteorologist absolutely crazy or just plain confused.  But first, let’s deal with the good news!

The visible satellite picture this morning shows that plenty of low clouds, whether that be fog or low stratus, still dominates much of the northern Mid Atlantic.  However, as dry air conditions to move in from the west, the low clouds will shrink in coverage, lift, and finally dissipate by late this morning into the early afternoon hours.  Any lingering precipitation will be isolated this morning and very light.  For those going to the Mets (double header!) and Phillies baseball games this afternoon and evening, weather conditions will be generally pleasant with light winds and temperatures in the 60′s and 70′s.  Basically a near average temperature day for the region.  Enjoy the comfortable conditions now, as this won’t be the theme going forward.

To the right is the ECMWF for Monday night.  Now, there are two very important and key features at 500 MB that will impact the northern Mid Atlantic’s weather for at least the next seven days if not longer.  The first is a deepening trough over northeastern Canada and Greenland, which is going to continue to be positioned anywhere from Greenland to the Canadian Maritimes.  The second feature is a building ridge over the Gulf Coast and Southeast.

Now, I’m using the ECMWF as an example, not my forecast, for the two features that will influence much of the eastern United States.  Note that over New England and the northern Mid Atlantic, the upper level pattern begins to converge.  Also note that 850 MB temperatures (color shaded) are tightly packed for this time of year.  This means that there is a surface boundary somewhere in the area, and that means trouble!

Here is how I see this pattern playing out.  The warm air mass is going to strengthen in coverage and in intensity over the next several days.  However, with the Arctic Oscillation going positive and the North Atlantic Oscillation remaining negative, a deep trough will be established over the northwestern Atlantic back through the Canadian Maritimes.  This leads to two primary surface features, high pressure off southern Mid Atlantic coast to the Bahamas and a stationary/warm front over the northern Mid Atlantic.  There in lies the problem!  South of this warm front, temperatures will be in the 80′s and 90′s with humidity increasing each day as the influence of the more Tropical air mass takes hold.  North of the frontal boundary, humidity will be significantly lower with temperatures in the more normal range of the 70′s for highs.  The difference in the air mass will be rather stark.  For example, Connecticut is setting up to be in a rather pleasant stretch of weather, especially to the northeast, with low humidity and temperatures in the 70′s in the afternoon.  Meanwhile, northeastern New Jersey will be in a far more humid air mass with dew points in the 60′s and 70′s along with highs in the lower 80′s to lower 90′s.  Throw in pesky mid level disturbances from the upper trough to the north, and the risk of thunderstorms, a few occasionally severe depending on the set up, will have an even more volatile impact on high temperatures south of the frontal boundary.  So the forecast from Saturday on through next week is not going to be easy and I expect changes from day to day.  Right now, if you live in the Philadelphia metropolitan area, prepare for a much more humid and active weather pattern.  If you are more towards New England, there is a higher potential for lower humidity and temperatures near normal.  Expect changes in the details of the forecast as we move forward!

So, welcome to summer of 2010!

For details on your location for the next seven days, visit the NY NJ PA Weather Seven Day Forecast!

05/29/10  10:24 AM

The day has started out cloudy with a few showers, however conditions will improve the rest of the day.

The old back door cold front is now rebounding as a very slow moving warm front, however this front is not very strong nor is the frontogenesis organized.  What that means is that the lifting is not very well supported to produce any wide rainfall.  However, as the low clouds break up through the morning hours, the lower and mid levels of the atmosphere will warm leading to some slight destabilization of the atmosphere, and thus the risk of widely scattered to isolated showers.  Many locations today will have dry conditions with scattered to broken cloud cover, and that’s it.  So the day is not completely lost.

The good news is that this front is going to move off the coast this evening and with it all the clouds too.  Note the areas of clear skies over western Pennsylvania and the Ohio Valley this morning, that is tomorrow’s weather.  With the clear skies will come significantly warmer temperatures with highs in the 80′s and even some lower 90′s throughout the region.  Similar conditions can be expected on Monday as high pressure slides over the region.

The next threat for severe weather will come on Tuesday with the approach of a very strong cold front.  There are strong indications that there will be plenty of upper level dynamics or lifting to support a wide spread outbreak of strong to severe thunderstorms along and ahead of the cold front on Tuesday afternoon.  The timing of the cold front is still debatable, but the threat for severe thunderstorms appears to be growing with each model run.  I also expected temperatures to soar into the 80′s and 90′s ahead of this cold front along with dew points in the upper 50′s to upper 60′s, leading to a very humid day on Tuesday afternoon.

High pressure and the return of a less humid yet warm air mass can be expected on Wednesday and Thursday ahead of the next strong cold front for Friday.  Temperatures through the period will average above normal with highs in the 70′s and 80′s.

05/24/10  4:10 PM

The upper low over the western Atlantic will have a variety of interesting impacts going forward for the rest of the week.

On the tropical potential side of this disturbance, there is  some concern that this upper low will gain some tropical characteristics over the next several days.  However, this influence will remain well out into the Atlantic and will have no direct impact on the northern Mid Atlantic.

Another more interesting development is the sinking air that is developing over the Mississippi Valley and Tennessee Valley this afternoon.  This sinking air is a direct result of the rising air to the east, and the influence of this sinking air is causing temperatures this afternoon in those locations to rise into the 80′s and 90′s.  A similar set up will take place over the northern Mid Atlantic, especially over eastern Pennsylvania and the Delaware River Valley, on Wednesday and Thursday with the potential for temperatures to rise into the mid to upper 80′s for many locations.

So, for tonight, low clouds will continue to linger over the northern Mid Atlantic with some areas of fog developing along the coast and in valley locations.  The fog may be locally dense along the coast where dew points will be enhanced due to the easterly flow.

By tomorrow, the upper low begins to drift further east into the Atlantic with drier air working southwest from the Great Lakes into the Hudson Valley and Connecticut first and then points south and east through the afternoon.  Clouds will break up by evening with dry conditions thereafter.

With clear skies, sinking air, and a warm 850 MB temperature regime; high temperatures on Wednesday and Thursday will spike into the 80′s and potentially lower 90′s throughout the region.  Dew points are expected to be in the upper 50′s to mid 60′s, supporting humid conditions as well.  Both of these days will be excellent for rushing to the beach!

A cold front will follow on Friday with the threat for showers and thunderstorms.  The bulk of the upper level dynamics with this cold front will be over New England, so I’m not expecting much of a severe threat.  However, a strong thunderstorm is possible.

A cooler, Polar enhanced Marine air mass will take hold for next weekend with variable cloud cover yet dry conditions.  Temperatures will return to near normal levels, in the 70′s for highs.

5/14/10  8:15 AM

This morning a warm front is moving through the northern Mid Atlantic with widely scattered showers and  overcast conditions.  The degree in which those clouds break up later this morning and early this afternoon will be a key factor in this forecast.

The air mass behind this warm front is certainly very warm and humid with high temperatures behind the warm front expected in the 70′s and 80′s with dew points in the surging into the upper 50′s to mid 60′s.  This air mass is clearly an unstable air mass over the southern Mid Atlantic, but what about the northern Mid Atlantic?

Well, the key in how unstable this air mass gets will depend on the degree that the low clouds over the region can break up.  At this time, I think the areas most likely to see clearing skies will be the immediate Philadelphia metropolitan area and central/southern New Jersey.  The more sun shine this afternoon between noon and 3 PM, the more likely severe thunderstorms will be an issue for the region.  The thunderstorms associated with this cold front this afternoon will be capable of heavy downpours, frequent lightning, large hail, wind gusts over 50 mph, and even a very isolated tornado.  I stress isolated here, but the threat for weak tornadoes needs to be addressed as there is some vertical wind shear at play, especially over the Delaware River Valley.  The cold front will exit into the coastal waters between 7 PM and 9 PM followed by clearing skies throughout the Philadelphia and New York City metropolitan area.

High pressure will take hold by tomorrow morning leading to an excellent stretch of weather for the weekend into early next week with clear skies, light winds, and temperatures in the 70′s for many locations.  Another area of low pressure will follow on Tuesday and Wednesday with widely scattered showers followed by another long stretch of clear skies and warm conditions for the end of next week.

For details on your local weather, visit the NY NJ PA Weather seven day forecast!

04/22/10  6:56 AM

An area of low pressure that produced showers and a few isolated thunderstorms last evening, is slowly departing into the Atlantic this morning.  Low clouds, fog, and isolated showers still linger over the northern Mid Atlantic, however conditions will rapidly improve over the next several hours as high pressure over central Ontario slowly builds into the northern Mid Atlantic.

Skies will clear by this afternoon with significantly improved conditions for the New York City and Philadelphia metropolitan areas.  With clear skies and a light westerly wind around 5 mph, temperatures will rise into the mid to upper 60′s for most locations.  I would not rule out a few isolated lower 70′s as well for the Delaware River Valley.

Tranquil conditions will continue through Friday and into Saturday afternoon as high pressure slides over the northern Mid Atlantic towards the Atlantic.  Clear skies, low humidity, and temperatures ranging from the mid 60′s to lower 70′s for highs and mid 30′s to upper 40′s for lows can be expected through the period.  However, the tranquil and comfortable conditions will not last long.

The water vapor satellite picture this morning showers a strong upper level low moving through the Rockies and heading towards the Plains.  This upper low will clash with the negative NAO pattern set up over the Canadian Maritimes to make for a rather nasty end of the weekend and start of next week.

A warm front will approach on Saturday night with increasing clouds and rain developing towards mid night.  Rain will continue through the day on Sunday and will be heavy at times.  Due to the strong blocking set up over the Atlantic via the negative NAO pattern, the warm front will stall over the Philadelphia and New York City metropolitan area leading to periods of moderate to heavy rain continuing through Monday.

The upper low will weaken over the Ohio Valley and give way to the stronger upper low over the Canadian Maritimes.  As a result, a surface low will develop and strengthen to the east of the Delaware coast Monday night through Tuesday morning leading to periods of heavy rain as well.

With the persistent easterly winds, there is a threat for some coastal flooding, however I think this threat will be small at this time as the winds are not very impressive with this system.  My main concern for this period will be the potential for heavy rainfall, which will easily exceed an inch and could approach two inches, leading to flash flooding of the rivers and urban locations once again.  I am especially concerned about this threat for northeastern New Jersey once again.

The low pressure system will exit on Tuesday afternoon with clearing conditions through Wednesday.  For a detailed seven day forecast, go here!