A stormy and volatile period begins

7:49 AM

There is plenty to discuss this morning in terms of storms, pattern development, and other interesting tidbits.  Naturally, all eyes are glued to this weekend where a potential snow event is displayed on some guidance.  I’m not as convinced of this potential, and I’ll explain why.  But first, let’s look at the surface map this morning.

6 AM Observations

High pressure has built into much of the coastal plain with generally clear skies and temperatures in the upper 20′s to lower 30′s over the interior and mid 30′s along much of the coast.  A Polar air mass is clearly in place.  I do find it interesting however that not one piece of model guidance has the presence of a weak area of low pressure over the Tennessee Valley that is moving northeastward, very slowly, towards the eastern Great Lakes.  This low pressure system is acting more like a boundary for what will be a stronger storm that is on the way by Thursday morning.  The development of this low, however will lead to winds backing to the southwest slightly faster than forecasted, and will lead to some moderation in the low level boundary layers already this afternoon.

Water Vaper Satellite-NOAA

As the cold front from yesterday, which provide periods of moderate rainfall throughout the Philadelphia and New York City metropolitan area, continues to sink over the Southeast and Gulf Coast; a new low pressure system is organizing over southeastern Texas.  The water vapor images this morning clearly show an area of low pressure organizing with moisture moving north towards the central Mississippi Valley.  The pattern still does not support the development of a true coastal low and will send the primary low towards the Hudson Valley on Thursday.  Regardless, the air mass will be too warm for anything but rain from this storm.  As the low pressure system races north on Thursday, a cold front will follow in the afternoon with temperatures crashing from the mid 50′s through the 40′s and into the 30′s in many locations by Thursday night.

ECMWF-Friday Night

With a Polar air mass in place and 850 MB temperatures below freezing, the environment is set up for a potential winter storm for the northern Mid Atlantic and New England.  A deep trough will be established over the eastern two-thirds of the nation with the trough axis neutral just to the west of the Mississippi Valley.  The cold front that moved through on Thursday will be stalled over the Gulf Stream, providing an area for low pressure development as the thermal gradient from the surface to 850 MB will be tightening.  Clearly, the potential for at least low pressure development along the coast is a strong possibility.  However, there is a lot about this situation that does not make me trust a scenario for a significant snowfall for much of the northern Mid Atlantic.

ECMWF-Saturday Night

The GFS and ECMWF has a general agreement on the overall set up of the upper level pattern.  One difference between the guidance on Saturday night is that the 500 MB trough over Ontario is displayed as a closed low on the GFS.  I belive the GFS is wrong on that idea given the changes on going to the west.  What the models do agree on is the lack of amplification of any ridge over the eastern Rockies.  I have this area circled in yellow.  A lack of any amplification of the ridge in this area means the down stream short wave over the southern Mid Atlantic coast can not deepen and is a progressive feature.  The idea of a strong low pressure system over the Gulf Stream to the east of New Jersey, as some guidance suggest, can not occur if the ridge is beaten down over the eastern Rockies as shown on all guidance, even the ensemble guidance.  Other issues that I want to touch on is that there will be significant boundary layer issue for much of the Philadelphia and New York City metropolitan areas, as temperatures for most locations with the exception of the western and northern suburbs of Philadelphi and New York City will be abover freezing based on most model guidance.  This strongly suggest an environment, should snow materialize, to be very wet and very difficult to accumulate.  One fact that makes me confident that a coastal low will form and will track off the coast is the well above normal water temperaturs off the northern Mid Atlantic and New England coast, which will strongly support a rising motion in the atmosphere and development of the low pressure system.  As we’ve seen all fall, when there has been a potential for a coastal storm, that coastal storm has materialized.

My thoughts for Saturday evening into Sunday morning is that an area of low pressure will track to the south and east of the New Jersey coast and roughly 250 miles southeast of Long Island.  This low pressure system will likely produce light rain and snow for the immediate coast with widely scattered snow showers over the interior.  I’m leaning on the ECMWF guidance and the Ensemble guidance which produces a more realistic match to the surface low track when comparing the 500 MB features.  I currently do not expect a significant accumulating snow event for the coast.

What would lead to a more amplified solution?  If guidance starts to illustrate more amplification of the ridge over eastern Rockies (zone in on Montana) then the trough can amplify more and colder air can be pulled towards the coast as the low deepens.  A storm track from North Carolina to the 70/40 bench mark would be needed due to the lack of a strong high pressure system over the eastern Great Lakes or St. Lawrence Valley.

Once this storm exits, high pressure will take hold for much of the region.  Dry conditions are expected for most regions, however a few stray lake effect snow showers may impact parts of the Hudson Valley and northeastern Pennsylvania on Sunday and Monday.  Temperatures will average below normal with highs struggling in the upper 30′s and lower 40′s for both days.

Extended Thoughts: MJO stalls

MJO Observations-11/29

Our tricky friend the MJO has thrown everyone for a loop once again and the result is plenty of uncertainty.  The latest observations, observed two days ago, has the MJO halting progression through stage six and backing towards stage five.  The MJO is firmly in a stage 6 phase, which again supports a pattern change towards a more El Nino like pattern.  The question is where does the MJO go from here?  My honest answer is I have no idea.  Let’s be frank, model guidance is of no help here is the GFS, UKMET, and other guidance does not have a strong handle of the progression of the MJO.  If the MJO tracks towards stage 5, then the idea of the Polar Vortex diving into western Canada as seen on the GFS and ECMWF is a very valid solution.  However, if one takes the course of the MOGREPS Mean, then the MJO will continue to progress at a lower amplitude towards stage seven.  This would lead to a colder pattern with the PV weakening and diving towards Ontario.  The truth is that where the MJO goes will have a significant impact on the pattern for December to one extreme or another.  If the MJO moves towards the El Nino supportive stages of 7 and 8 this month then those going for a major cold pattern for the East (active storm track too) will be correct.  If the MJO goes towards stage 5, then a more La Nina type pattern is supported and the results seen on the 00Z GFS and ECMWF become a reality.

30 MB temperatures

Additional news, the warming in the stratosphere is backing off currently and falling fast from the historic above normal levels seen through November.  Temperatures are still well above normal, but are not at the historic levels that have been observed.  The strongest area of warming is currently over western Pacific, just off the Japan coast, strongly suggesting a negative EPO pattern with a warm temperature environment extending towards North America.  The latest ECMWF guidance for the stratospheric temperatures suggest that temperatures will stabilize and begin to warm again.

So there will be plenty to keep an eye on through the next several days.  The forecast is at a volatile state and changes in the guidance can be expected.  Honestly, would you have it any other way?

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