9:29 AM

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A lot of action is starting to unfold for the northern Mid Atlantic.  As we all know, there is a snow threat for this weekend that has the potential to produce a significant snowfall for much of the northern Mid Atlantic.  Then there is the threat influence of the MJO in phase 7 and the continued warming of the stratosphere.  Well, let’s get to it!

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9:11 AM

A light snow event is going to unfold on Friday morning, but the details remain uncertain as much depends on the evolution of mesoscale parameters.  So this morning, I’m going to try to clear some of the fog and mist of this time period and discuss the potential that exits and why it exist.  This isn’t about models, it’s about meteorology.

7:33 AM

I wanted to take some time to address some medium range thoughts I have involving the evolution of the pattern for the start of November as I know that sometimes my writing of this time period can be misinterpreted out there on the weather boards and what not.

First, for those new to NY NJ PA Weather (Welcome!!), I want to give you some back ground on my thoughts of medium and long range forecasting.  You won’t find sensational statements or vague phases here.  My philosophy with this range of forecasting is to try to introduce ideas slightly outside the box and to consider all options.  I have a general distrust with model guidance beyond 180 hours due to the decrease in resolution and the compound problems of initialized error in this range.  I also don’t bother with guidance beyond 240 hours.  If you don’t like what you see on the GFS at 300 hours, wait a run, it will likely end up differently.

ECWMF- Northern Hemisphere Sunday 11/8

I’ve been studying the model guidance for the end of next week and I’ve been advertising for some time the idea of a cold (relative to normal) and stormy start to November.  Why?

Well, there are a few key features that keep on developing on the model guidance that teleconnect very well with this thinking.  On the cold side, the Cahir’s Connection continues to show up in the guidance.  The Cahir’s Connection is a ridge that develops between 60E and 60W and north of 50N.  When this ridge develops, colder air is forced into Canada and much of North America.  Meanwhile, the continued development of the upper low between the Aleutian Islands and the Gulf of Alaska will support a ridge over the West, thus supporting a trough over the East for the start of November.  The active Sub Tropical Jet Stream that has been a persistent theme for much of the Fall will interact with disturbances diving south into this trough as well.  Guidance does not show much in the way of precipitation yet, but the signs are there for a potential clash of the air masses towards the end of this forecast period.

Now, this pattern is going to lock in.  The transient nature of the upper low around Alaska just will not allow for ridge west/trough east pattern to remain in place for long.  I should note, this also means the idea of a prolonged ridge over the West is not well supported either.  The keep phase here is progressive and progressive means that a lot of disturbances are going to be racing through the East as the pattern attempts to stabilize.  In the meantime, expect several cold shots to impact the northern Mid Atlantic as each trough redevelops and lifts north and east.

I admit I don’t have much support to say this, but I don’t think that November will feature persistent warm stretches at all.  In fact, I think November will average near normal.  Why?  Well, the development of a positive PDO and the current day to day changes in sea surface temperature anomalies over the Gulf of Alaska and Aleutian Islands continue to point  me in the direction of keeping the Upper Low in place around the Aleutian Islands for some time.  As a result, the potential for a ridge over western Canada (note I said Canada, suggesting a split in the jet streams) would suggest a northwesterly flow towards the northern Plains, Great Lakes, Northeast, and northern Mid Atlantic.  El Nino pattern rarely feature Southeast ridges and I think the support for any such ridge will weaken as the month continues.

So those are my thoughts for now.  For those interested in the rest of November and this winter, the winter seasonal forecast will be out on November 1st for all members.

9:05 PM

Fall is in the air, literally, as a strong Polar air mass builds into the Philadelphia and New York City metropolitan areas this evening.  I could smell the change in the air mass as the air just smelled cleaner, kind of that fleshly raked leaves type smell that I loved when I was a child.  Temperatures tonight are expected to fall into the lower to mid 40′s over much of the coastal plain and lower to upper 30′s over much of the interior.  In fact all over southeastern Pennsylvania with the exception of Philadelphia and  northwestern New Jersey are under frost advisories tonight.  Locations further north have already had a freeze, so there is no need for the advisory.  Anyway, this new air mass is already setting up a thermal gradient that will certainly lead to a very active end to this week.

Water Vapor Satellite This Evening

The water vapor this evening shows us some important details going forward over the next several days.  Our first disturbance of our two part storm is already pushing through the northern Plains and is rather impressive in structure already.  This disturbance is not expected to be a closed upper low, however the latest images show that this disturbance is not far from the closed upper low stage to begin with.  We also can clearly see (and I’ve highlighted) that the Sub Tropical jet stream is alive and well, with plenty of moisture driving from the south Pacific into the Mississippi Valley.  Clearly the upper level trough that will drive our two low pressure systems will not be lack moisture given the evolution of the pattern.

Tonight I want to discuss my thoughts on this storm.  Anyone that has seen the models know that they follow the same general idea, but with various results.  The GFS is all over the place with a miss of the storm on last night’s 00Z run to a two storm blasting now.  The ECMWF remains constant with a two storm impact on the forecast area as well, but with various degrees of strength between the two low pressure systems.  In fact, the 12Z guidance from both models are pretty much in the park of the overall forecast.

So here is how I expect this storm to work out.

Through the day on Wednesday, an area of low pressure will continue to organize over the Mississippi Valley and drive towards the Tennessee Valley by Wednesday evening.  On Thursday, a series of weak low pressure systems will develop from the Gulf Coast through the Southeast coastal waters.  Eventually, one low pressure system will become the primary low off the Virginia coast and drift north and east towards the New Jersey coastal waters on Thursday evening.  Again, this is all with the first disturbance.

I expect periods of heavy rain to begin on late Thursday evening and continue on through Friday afternoon.  The heaviest rainfall should be focused from eastern Pennsylvania, throughout all of New Jersey, and the immediate New York City Metropolitan area.  In short, locations over the interior can expect the least amount of rainfall and overall impact, while locations along the coast are in for one nasty morning commute on Friday.  Rainfall amounts along the coast will range from 1 to 2 inches of rain with the southern and central New Jersey coastline possibly reaching up to 2.5 inches of rain in some isolated locations.  I’m expecting wind sustained from the Northeast around 15 to 30 mph with gusts up to 45 mph at times.  Meanwhile, temperatures will be locked into the upper 40′s to lower 50′s through the period.

A brief note here about precipitation type.  It is true that the air mass is frankly cold for this time of year.  In fact, for much of this storm, 850 MB temperatures over interior eastern Pennsylvania, northwestern New Jersey, the Hudson Valley, and interior Connecticut will range right around 0°C while the heaviest precipitation is falling.  When low level forcing develops and moves through these locations (experienced as heavier rainfall), the atmosphere will be able to cool enough to support periods of frozen precipitation, although very briefly.  With the exception of the highest elevations, I do not expect any sort of measurable accumulation from this frozen precipitation.  So yes, there is a chance of a burst of sleet and snow on Thursday night, but no accumulation is expected as rain and the above freezing warmer air will overwhelm the colder air aloft.

For those who are going to the Yankees game on Friday night, you might just luck out.  The first low will exit the region by late Friday afternoon with the worst impacts over by the evening in my opinion.  While showers will still linger over the coast, the heaviest rainfall will be over by 8 PM.  However, a raw northeast to north wind will remain around 10 to 20 mph and temperatures will be around 50 degrees.

While the Yankees and Angels slug it out in the Bronx on Friday night, a strong disturbance will be diving into the new trough carved out by the first disturbance.  Disturbance number 2 is expected to be stronger with a mature closed upper low.  This upper low will have strong PVA or strong lifting rotate from the Southeast coast to the New Jersey coast on Friday afternoon, which will force the development of another coastal low over the Virginia Capes.  Now, model guidance has been rather sketch about the development and track of this low pressure system, but we do know that a new low pressure system will form.  We do know that a second disturbance will dive into this trough and intensify, to what degree can be debatable.  We also know that the first storm will act as a slowing agent for the overall pattern, albeit briefly.

Taking this considerations into account, this evening I continue to think that a second low pressure system will form off the Mid Atlantic coast somewhere off the DELMARVA Peninsula on Saturday morning.  This low pressure system will then slowly track northeast towards eastern Long Island on late Saturday afternoon through Sunday morning, producing heavy rainfall over both the Philadelphia and New York City metropolitan areas.  There will be a strong moisture advection from this second storm from the Atlantic, so I would expect a jet of precipitation moving from the Atlantic through New Jersey and into eastern Pennsylvania which will slowly progress northward and expand through the evening hours on Saturday.  Once again, strong winds can be expected from the east and northeast around 15 to 30 mph along with very cool temperatures.  Rainfall amounts for the forecast area will range from 0.50″ to up to 2″ throughout the forecast area.  This rainfall will not be as uniformed as the first storm as two factors will impact the lifting of the precipitation.  The strongest upper level forcing will be found along the immediate coast, which is one area that could expect heavy rainfall.  However, orographic lifting will have to be considered for interior eastern Pennsylvania as the easterly wind flow will be stronger and deeper than the first storm and will enhance rainfall as well.

By Sunday morning, the second storm will begin to pull away with lingering showers up through the early afternoon before skies begin to clear.  I expect flash flooding to be a threat with this storm along with high wind impacts, minor coastal flooding, and small craft advisories.  Total rainfall amounts throughout the region has the potential to range from 1 to 3 inches, especially along the coast from both of these storms.

Naturally, a lot can still change in the evolution and development of these two storms and I’ll do my best to keep you all updated on the latest information.  Depending on the 00Z guidance late tonight, I will start to send out text alerts for the first storm by early tomorrow morning.

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.