December 29th-30th Potential Overrunning event

Since we are 5-6days away here is the set up for the 28th into the 29th.  What appears on all models is a Low pressure that passes north of the GL and into the Canadian Maritime Sat into Sunday.  With it it drags a cold front through our area late Sunday into early Monday.  A series of LP waves associated with the sub tropical jet look to develop and ride along that frontal boundary.  As of now the CMC and GFS-P are a little faster with pushing the frontal boundary (not by much) through our area and also push it further south when compared to the Euro.  In the wake of the LP that passes to our N and eventually East an Arctic HP builds in during this same time frame.

00z EURO:
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00Z CMC:
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00z GFS-P:
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Currently there are differences in just how far north and east the LP moves, as well as just how strong it is as it does so.  As a result the timing and positioning of the frontal boundary is different between models as well as within individual runs of individual models.  In addition there are differences in the positioning and the strength of the Arctic HP building in over the top (or to the north) and into the region in its wake.  Both the result of the LP and the result of the HP, and the timing of both will be critical pieces(but not the only critical pieces) to this puzzle to whether or not we get a warm or cold soln and/or a wet or dry soln.   ie: if the LP is stronger and pushes to far east and drags the front too far south the HP builds in stronger and suppresses the moisture stream like the GFS-P and the CMC seem to show to our south.  

The precip we get from this event(IF we get any) will come in two ways.  First the passage of the cold front.  This will most likely result in light rain showers for most if not all of us late Sunday into Monday.  As the cold front pushes through the region it will spawn rain showers as it pushes pretty warm air out.  I don't expect much in the way of frozen precip with the cold front pushing through.  Second, as you can see from the images above there is a very active STJ (sub tropical jet) with a moisture feed coming strait out of the GOM (gulf of Mexico).  A series of weak LP waves will develop along the eventual stalled frontal boundary mentioned above, and move E to NE along it.  With it comes all that moisture.  Again currently there are still major differences in just how weak or strong these waves are, as well as the timing of them which are also critical pieces to this puzzle.      

This type of set up was not all that uncommon last year.  They are typically referred to as over running events.  First you have a wedge of cold dense air (cold front) that sets up and stalls.  As the waves of LP develop they ride along the boundary from East to west and the counterclockwise flow of air around a LP center drags the warmer moist air to the south of the cold front boundary and forces it up and over the wedge of cold air stuck in places by a process known as warm air advection (WAA).  As the warm moist air rises it cools, condensation occurs, and precip falls.  This precip can be enhanced by two ways.  1) strength of the LP.  The larger the gradient between LP and HP the stronger the forcing; therefore the stronger the moisture transport.  or 2) The baroclinic zone.  This is the temperature difference north of the frontal boundary compared to south of the frontal boundary.  If you have a drafty door leading to the outside in your house you have experienced the movement of air created by a baroclinic zone in the winter.  You do not have to have strong LP to get a significant moisture event as the physics of moisture transport are driven(or enhanced) by the temperature gradient rather than a pressure gradient.

Where exactly the frontal boundary sets up as well as how strong or weak the LP waves are as they move along it will dictate how warm or cold the mid and upper levels of the atmosphere are in your back yard and dictate if the precip falling is rain, freezing rain, sleet or snow.  As of right now there are still major differences in the models with all of these scenarios so do not take any one soln as gospel at this time.  If last nights 00z Euro were to verify verbatim the area will see a wide spread 3-6" with areas in C NJ seeing as much as 6-10+ possible with this event.  If the 06z GFS-P or the 00z CMC were to verify then the area would see passing showers Sunday eve into early Monday with the cold frontal passage and then stay dry through Tuesday.  

So please please please don't get to excited or sad just yet.  I hope we all stay even until after Christmas.  There is also a possible second event for the 31st-1st as well but first we get through the Midwest Santa Storm this week (or what ever it was called), Then we see how the overrunning event evolves for early next week, and then we can move to the NYE potential (or lack thereof).

nice write up sroc4. Lets keep our fingers crossed.

NWS Upton disco agrees nice work sroc.

FOR NOW GOING WITH CHANCE POPS SUNDAY NIGHT AND SLIGHT CHANCE POPS
MONDAY TO REFLECT POTENTIAL WAVES OF LOW PRESSURE PASSING TO THE
S...WITH MAINLY SNOW EXPECTED ACROSS N ZONES...AND RAIN CHANGING
TO SNOW ACROSS S ZONES. STILL QUITE A BIT OF UNCERTAINTY ON EXACT
TIMING/STRENGTH/TRACK AND NUMBER OF THESE WAVES. FOR NOW BEST TO
CHARACTERIZE WEATHER FOR EARLY NEXT WEEK AS POTENTIALLY
UNSETTLED...WITH A BETTER CHANCE FOR SNOW THAN RAIN AT MOST
LOCATIONS...IF ANY THING FALLS AT ALL. GIVEN LARGE DEGREE OF
UNCERTAINTY...IT IS TO EARLY TO SPECULATE ON WHAT...IF ANY IMPACT
THERE WILL BE FROM THESE POTENTIALLY MULTIPLE COASTAL LOWS PASSING
TO THE S.

FWIW TWC has forcasted 28th at night a inch or less and Monday 1-3 for yonkers, NY. What model does TWC hug?

jmanley32 wrote:FWIW TWC has forcasted 28th at night a inch or less and Monday 1-3 for yonkers, NY.  What model does TWC hug?

Most of those are automated forecasts directly from the GFS

Upton for next week

FOR NOW GOING WITH CHANCE POPS SUNDAY NIGHT AND SLIGHT CHANCE POPS MONDAY TO REFLECT POTENTIAL WAVES OF LOW PRESSURE PASSING TO THE S...WITH MAINLY SNOW EXPECTED ACROSS N ZONES...AND RAIN CHANGING TO SNOW ACROSS S ZONES. STILL QUITE A BIT OF UNCERTAINTY ON EXACT TIMING/STRENGTH/TRACK AND NUMBER OF THESE WAVES. FOR NOW BEST TO CHARACTERIZE WEATHER FOR EARLY NEXT WEEK AS POTENTIALLY UNSETTLED...WITH A BETTER CHANCE FOR SNOW THAN RAIN AT MOST LOCATIONS...IF ANY THING FALLS AT ALL. GIVEN LARGE DEGREE OF UNCERTAINTY...IT IS TO EARLY TO SPECULATE ON WHAT...IF ANY IMPACT THERE WILL BE FROM THESE POTENTIALLY MULTIPLE COASTAL LOWS PASSING TO THE South

GFS Para likes this storm. Rain to snow.

Do you think the heavier precip has a chance at getting further north, I know its early but overall look at this time?

It's a fight between the PV and the southeast ridge. Heavier precip north would result in warmer temps.

Frank_Wx wrote:It's a fight between the PV and the southeast ridge. Heavier precip north would result in warmer temps.

Looks like a scenario from last March where the cold pushes the storm track further south and we get little to nothing. Hopefully we can skate the line and get snow. After the last month of disappointment it would be a kick in the teeth and pretty ironic if we get cold that's too strong and forces storm too far south and east. Lets hope we get one our way for once. A few inches could help temps stay cold for next storm around New Years and so on.....

We are having extended family over where I live Sunday afternoon to Sunday evening which we usually do between Boxing Day and New Year's but it's exceptionally big this year as one of my cousins recently got engaged. If this does happen, I really hope it holds off until after it is over. Keeping my fingers crossed...

Euro tracks the surface  low to our west and is mainly rain, then tries to transfer off the coast. I still like where we stand with this storm. Euro has been inconsistent all year

Certainly a thread and needle type event. Too far north= rain. Too far south= dry. Just right=snow. Going to be tough to nail down this event.

See Jman, you asked to see what precip further north will do and look what the Euro did. All your fault

There has to be something going on with the models, right? I do not remember a period like this of drastic run to run changes and very little consistency or agreement among eachother. It's absurd

Yeah it is pretty crazy Frank. I also noticed with the 12z Euro the Xmas storm is about 8mb stronger than the 00z by the time it's spinning over the GL (around 6z 25th and the next 6-12 hrs, and is a bit further west. Euro is def unsure right now.

That's why I stated in that thread IMO the winds could be stronger than 35mph gusts. Frank sorry bout that should known better duh, warm air drawn in pushes PV north. I don't think I have the power to change weather, if I do then lets make this a all out nuts storm lol

syosnow94 wrote:

Frank_Wx wrote:It's a fight between the PV and the southeast ridge. Heavier precip north would result in warmer temps.

Looks like a scenario from last March where the cold pushes the storm track further south and we get little to nothing.  Hopefully we can skate the line and get snow.  After the last month of disappointment it would be a kick in the teeth and pretty ironic if we get cold that's too strong and forces storm too far south and east.  Lets hope we get one our way for once.  A few inches could help temps stay cold for next storm around New Years and so on.....

Tell me about it. This is def possible. We need baby bears porridge....not too hot, not too cold, but jjjjust right.

Upton NWS discussion:
FOR NOW...THE ECMWF FOR SUN AND MON APPEARS TO BE AN OUTLIER BASED
ON THE GFS...GFS ENSEMBLES AND 00Z ECMWF. THE FCST THEREFORE IS
HEDGED MILDER ON SUN...AND COLDER MON WITH INCREASED SNOW
CHCS...SIMILAR TO THE 00Z ECMWF SUGGESTION.

Euro ensembles are all over the place, but the mean brings 1-3 inches to NYC.

NWS Upton updated forecast for me on LI for next week's possible event.
FOR NOW...THE ECMWF FOR SUN AND MON APPEARS TO BE AN OUTLIER BASED ON THE GFS...GFS ENSEMBLES AND 00Z ECMWF. THE FCST THEREFORE IS HEDGED MILDER ON SUN...AND COLDER MON WITH INCREASED SNOW CHCS...SIMILAR TO THE 00Z ECMWF SUGGESTION.

Sunday A chance of rain and snow. Mostly cloudy, with a high near 45. Chance of precipitation is 40%.

Sunday Night A chance of rain and snow. Mostly cloudy, with a low around 29. Chance of precipitation is 40%.

Monday A chance of snow. Mostly cloudy, with a high near 37. Chance of precipitation is 30%.

Monday Night A chance of snow. Mostly cloudy, with a low around 27. Chance of precipitation is 30%.

For what its worth, the 18z GFS has a snowstorm for monday. Let's see if the Euro gets on board later on. At least we might have something to track.

yeah nutley but the para GFS which Frank goes by does not. It actually has the storm wayyyyy south.

GFS is way south compared to the 18z GFS run for Sunday lol. GFS has a different solution every time lol

Snow88 wrote:GFS is way south compared to the 18z GFS run for Sunday lol. GFS has a different solution every time lol

Stop using it. Stick with Para