NY NJ PA Weather Forecasts

Active period of weather marks beginning of pattern changes

7:10 AM

This morning, a strong disturbance at 500 MB is moving towards the Mid Atlantic coast.  This disturbance is going to be forced to move quickly through the Philadelphia and New York City metropolitan area today, but not without some impact.

Overcast skies can be expected through the day with scattered showers approaching from the southwest by late in the morning over southern New Jersey and the rest of the northern Mid Atlantic through the afternoon and evening hours.  Although a few heavy downpours will be possible in a few showers, the majority of the rainfall will be light.

The disturbance today is being forced to move so quickly to the north and east dues to a much stronger

upper level trough diving into the Plains and Mississippi Valley.  The upper level trough and the disturbances within this trough will have a significant impact on the forecast period through Thanksgiving and into Friday.

Tonight through tomorrow, the coastal low this morning will exit towards New England with lingering low clouds through the day on Tuesday.  Temperatures will average near normal for the most part, but will feel a bit cooler due to the persistent northeasterly wind.

A weakening cold front will move through the Philadelphia and New York City metropolitan area on Wednesday morning with a few widely scattered showers, but otherwise little if any impact.  Most locations will remain dry and relatively comfortable.  However, this cold front will be a key component to a more significant storm for 48 hours later.

Now, there are key differences between the GFS guidance the ECMWF guidance from this point on.  The GFS tries to produce a phased solution and tries to pull the surface low pressure system into the Ohio Valley.  The ECMWF does not, and thus produces a more coastal solution to the forecast period.  Both guidance however ends up with the surface low pressure system over central New York by Friday afternoon.  I’m siding with the ECMWF solution because of the placement of the strong PVA on both guidance.  On the ECMWF, the best dynamics is focused towards the coast.  The GFS at relatively the same time period also focuses the strongest PVA towards the coast, yet forces the coastal low from the North Carolina coast towards western Pennsylvania on Thursday night and Friday morning.  At this time, I’m not inclined to follow that solution given the other factors.  When the PVA is directed towards the coast, the solution 99% of the time is a coastal low.  So here are my thoughts for Thanksgiving and for “black” Friday.

High pressure over New England will keep conditions dry on Wednesday night through Thursday morning.  Clouds will increase from south to north as the strong disturbance from the Mid West dives towards the Tennessee Valley, supporting the development of a coastal low along the stationary front over the Mid Atlantic coastal waters.  As the day continues clouds will continue to increase along with a northeasterly wind into the 10 to 20 mph range.  By Thursday night, the coastal low will move from the Virginia coastal waters towards the New Jersey coastal waters.  During this time period, the low pressure system will deepen from a 1008 MB low to a 998 MB low, which is a significant period of intensification.  I expect rain, heavy at times, to move from east to west over the Philadelphia and New York City metropolitan areas.  The rain should initially impact southern New Jersey and continues to progress north and west through the night.  As the low pressure system intensifies, colder air to the west will be drawn towards the coast.  This is where the forecast gets a bit tricky.

The interaction of the cold air and this coastal storm will allow the storm to deepen further, down to perhaps a 996 or 994 MB low over the Hudson Valley by Friday morning.  The track of the low will mean that the best potential for any frozen precipitation will be found over northeastern Pennsylvania and northwestern New Jersey.  However, I want to stress that I do not expect any significant accumulations in the lower elevations at all.  The highest elevation above 1500 feet may be a different story, but I want to wait until the time period for this storm gets closer before addressing accumulation totals, if any.  Timing in terms of any type of frozen precipitation will be a major factor.

As the storm moves north, wrap around precipitation and strong cold air advection will bring a threat of rain and snow to the entire forecast area.  Again, no accumulation is expected, but don’t be surprised if you see some snowflakes in the air along with some raindrops on Friday afternoon.  This storm will also provide very windy conditions and the potential for some minor coastal flooding on Friday morning.

As the major coastal storm pulls into northern New York, high pressure will take hold for Saturday and Sunday with tranquil conditions.  Temperatures will average near normal through the weekend ahead of the next stage of cold air.

Extended Thoughts:

As expected, model guidance is having all sorts of interesting solutions beyond day 7.  The ECMWF the past two runs first tried to phase the Sub Tropical Disturbance with the Polar jet stream over the West, thus pumping a large ridge into the East.  The 00Z run, completely different with a ridge attempting to establish itself over the West coast, a major negative EPO pattern being hinted at, and a wide, cold trough over the eastern two-thirds of the nation.  You can’t get much different than that from run to run, and this is the most accurately scored model guidance for this period!  The point is that if you relay on model guidance for you extended forecasting, you are going to drive yourself nuts.

I’ve been keeping an eye on the MJO, which was supposed to die based on the majority of model guidance but is instead trucking along into Phase 5.  The MJO wave has been dampened as it moved into phase 5, but still very much alive.  Now, if the MJO reaches phases 6 and 7, a cold phase in the pattern can usually be expected, especially in El Nino years.  Considering the recent trends of the MJO and the recent trends of model guidance to push the MJO into that direction, one would be wise to lean on the cold side of the extended forecast.

Further, stratospheric temperatures are still well above normal, in some cases record breaking, at 10 MB down to 70 MB, which continue to suggest a favorable environment for blocking.  It should be noted that the once declining 10 MB temperatures have now spiked once again, while the rest of the lower troposphere remains in record breaking territory.

These indicators and the resulting atmospheric waves associated with these developments point me to a pattern that is cold, not warm.  However, I caution once again about any historic cold or sustained cold ideas.  All the surface and upper level data I am following suggest a more gradual step down to cold for December.  A slow descend into a very active and cold pattern for much of winter, however it will take some time to get there.  This month is all about that process.  I don’t expect any sustained ridges in the East nor above normal conditions.  However, with each push of cold air, there will be a step back towards moderation ahead of the next cold air mass.  This is due to the fact that a cryosphere must be established over southern Canada and the northern Plains to limit moderation of air masses.  Also the blocking necessary for the winter pattern for January and February has to be given time to actually develop.  Make no mistakes, we are in the first stages of this pattern change.  However, those hoping for a quick jump into a pattern that will likely make many snow lovers happy, should instead expect a slow and gradual change.