HISTORIC SNOWSTORM DEC 19-20 MD /VA/ NC NOW LIKELY
12/18/09 1430 EST
EMERGENCY ALPHA #1 …. EMERGENCY ALPHA #1
WXRISK.COM – has UPGRADED the CONDITION ALPHA #1 to EMEGENCY ALPHA …effective for the approximate time from 0000 12/19/ 2009 to 2000 EST 12/20/2009 for the Likely occurrence of a H.E.C.S. (Historic East Coast Snowstorm)for the Following areas of concern:
… NC west of I-85 and NORTH of I-40 (Henderson – Durham – Greensboro- Winston Salem Hickory Ashville) …
… All of VA except for Hampton Roads…
… All of MD except for western 2 counties of MD…
… All of DE except for far northwest portion…
… All of MD… except for far western MD…
… All of DE…
… All of southeast PA…
… Southern and central NJ
Southern NYC and ALL of Long Island
Far Southern CT far southern RI Martha Vineyard and Nantucket and Cape Cod Mass…
EMERGENCY ALPHA has been expanded into the NYC metro area and eastern northern NJ… ALL of LI.. far southern CT and RI. Areas JUST to the North will see SIGNIFICANT snow accumulations But NOT enough to met the threshold criteria of a HECS event. The snowfall ” shield” will feature Rapid DROP off in snow accumulation over very short distances to the North and West of the warned area. Thus Interior southeast NY and Interior CT might only see 3-6″ snow amounts.
EMERGENCY ALPHA shall by declare whenever the atmospheric pattern and Model data has shift into a high likelihood for a H.E.C.S. event to occur over a given period or a specific Location along the East Coast of the CONUS from Atlanta GA to Augusta ME and east of the Appalachian Mountains.
CONDITION ALPHA means that WXRISK.COM thinks a K-U / highly ranked NESIS ( KU= Kocin and Uccellini case book of 36 Major NE US snowstorms and NESIS = Northeast Snowstorm Index Scale) event is about to Occur. Weather Hobbyists… out of control News Media… Professional Meteorologists… Businesses that can be affected by Major weather events and the General Public should be aware that something Major and very serious is about to happen because of Major or recording breaking Winter storm.
SITUATIONAL ANALYSIS :
I am extremely gratified to see in the consensus from other private forecasters and meteorologists as well as NWS move in the direction which I have been going for the past several days.
The NW shift showed by the 12z and 18z Models on Thursday have NOT held my reluctance to not increase the snow amounts significantly over northern New Jersey SE PA NYC CT and eastern Massachusetts on 1ST GUESS and 1st CALL has proven to be the correct one based upon the new data during the overnight hours and at 12z.
The main issue of uncertainty continues to be the Northwest side of the precipitation shield at how far will extend to the north and west of the major cities in the I-95 corridor. There is finally been a significant consensus in the numerous weather models over the last two runs–0z and 6z about where the Noreaster is going to be Saturday morning… and I believe that consensus is showing up nicely on the 12z runs of the RGEM ECMWF GFS and to a lesser degree with the NAM and UKMET.
This forecast is based upon several key premises… among them being that the 850 Low will track over and just to the north of Cape Hatteras close to Elizabeth city / Nags Head THEN turn N or NE and power well be Virginia lower Maryland Eastern shore during the day on Saturday. This will result in the precipitation shield being set up in a crescent shaped curve from DC and Patuxent River into NJ PHL NYC LI CT and southern MASS.
Synoptically the PV that has been stalled over southeastern Canada is beginning to weaken and get sheared apart which can be clearly seen on the short range models over the next 24 hours. This last-minute weakening of the polar vortex has allowed the northward jump in the surface and the 850 low in the models we have seen over the last 24 hours. As I discussed many times in the Condition Bravo and Condition Alpha statements this was a key portion of the forecast and my focus on this particular aspect of forecast appears to have been correct .
Some portions of the forecast had been quite easy to make given the overall pattern…. for example forecasting heavy snow over far northwestern NW much of western and west central Virginia and up towards the DC area is not really been difficult forecast issue for me. That part of the forecast is been a easy Win. Even for the Washington, DC metro area the data for early early on indicated that region would see significant snow but the main debate was going to be whether or not the snow in mid-December will qualify as a Major or Historic snow.
Likewise the concern that southern New Jersey especially over southwest portions of southern New Jersey and eastern Maryland would see a major or historic snowfall has also been rather easy to detect.
There are still areas of uncertainty still left to be figured out. One of them actually has to do with central Virginia as for reasons which are hard to figure out many the media and NWS forecasts continue to show shockingly low snow amounts even after one assumes several hours of sleet Saturday morning over the Richmond Metro area… which is a dubious assumption at best.
For example if one assumes that by tomorrow morning over RIC there is 2-4″ of snow in the ground which is what all the model data showing… then we have several hours of sleet mixed in… from say 5am to noon… then it turns back to all snow — most of the model data has that occurring before noon– and it snow until 1-4 am sunday… and again most of the model data shows that heavy snow as well… how do not end up with 10 inches?”
Likewise across the northern end of middle Atlantic region trying to figure out the stratification in the snow forecasting bands is going to be a real problem. The snow amounts differentials between Harrisburg and Hagerstown… York and BWI… RDG and PHL … ABE and TTN…
Dover in far NW NJ and EWR…. between POU and LGA… BDL and ISP… and BOS vs Taunton is going to be a very interesting challenge. There is no doubt that even though this is my last call they are going to be some areas where I will Bust.
DETAILED ANALYSIS
1. The event itself is a classic text book MILLER A event and develops as a PJ (Polar Jet) short wave Phases with the short wave in the STJ (subtropical Jet) over the Delta and Gulf coast region..
2. NAO phase — severely Negative with huge multi contoured 500 mb Ridge over Greenland that extends west into Labrador. This is arguably one of the best and idealized –NAO / East coast set ups in the past 40 years.
3. 50/50 LOW — IDEAL. Even though the large powerful and very deep PV that is situated over New Brunswick Canada is NOT a 50/50 Low …it is in effect ” acting” in this synoptic sense as if it was a large 50-50 Low. The position of this feature over southeastern Canada insures that the confluence own than the Polar Jet has set up across central New England which is significantly idealized or textbook KU set up for northeast US snowstorms.
4. PV feature; Intense and displaced well to the south. The displacement of the PV into northern Maine and far southeastern Canada is a significant synoptic development and is often a precursor that skill the medium-range forecast is look for in forecasting the possible development of the major East Coast snowstorm. The reason for this is that it becomes impossible to keep and sustain the PV this far to the south unless something else is going on in the atmosphere… something significant which in this case counts as the REX Block -NAO over Greenland.
5. 850 LOW TRACK: over ILM and between HSE and ECG … then turning to the NE and crossing 70 west Long Line at 38N.
Weather models agree that the 850 Low will come further North Once it cross the 75 wes Long Line at cape Hatteras/ Nags Head. Thus Northern VA DC Metro area intro central MD and BWI metro regions are now in the Heavy snow Band.
This 850 Low track now does match two of the 33 – Now 35 — KU snowstorms.
6. SPLIT FLOW CYCLOGENESIS .
http://1664596.sites…clogtypes/3.jpg
7. ANALOG at 500 MB to this event:
JAN 27-29 1922 (the Knickerbocker storm)
JAN 23-24 1940
FEB 11-12 1983
KU VALUE TOP 10 EVENT NESIS VALUE 7.0
WHAT CAN GO WRONG
There is of course still the possibility that the 850 low might track much close to the coast… crossing north of Elizabeth city and passing very close to Wallops Island. This would significantly impact the snow amounts over Eastern Virginia including the Richmond Metro Area and the Lower MD
Eastern shore… and raise the risk of sleet getting into southern New Jersey.
On the other hand such a track would increase the snow amounts over Philly… Northern NJ,…. ABE NYC into POU … and into BDL and BOS.
12/17/09 1930 est
SET CONDITION ALPHA #1 …. SET CONDITION ALPHA #1
WXRISK.COM has UPGRADED the CONDITION BRAVO #2 statement to CONDITION ALPHA …effective immediately for the approximate time from 0100 12/19/ 2009 to 2000 EST 12/20/2009 for the Likely occurrence of a H.E.C.S. (Historic East Coast Snowstorm) for the Following areas of concern:
… NC west of I-85 and NORTH of I-40 (Henderson – Durham – Greensboro- Winston Salem Hickory Ashville) …
… All of VA except for Hampton Roads…
… All of MD except for western 2 counties of MD…
… All of DE except for far northwest portion…
… All of MD… except for far western MD…
… All of DE…
… All of southeast PA…
… Southern and central NJ and eastern Long Island…
… Martha Vineyard and Nantucket Mass…
It does NOT include Southeast NY…… NYC…… northern NJ… western LI.. CT or Boston Meto area. However these areas are LIKELY to SIGNIFICANT snowfall… 4 to 8” still exists for NYC southern CT… and western Long Island.
CONDITION ALPHA shall by declare whenever the atmospheric pattern and Model data has shift into a much more favorable state for M.E.C.S. or H.E.C.S. event to occur over a given period or a specific Location along the East Coast of the CONUS from Atlanta GA to Augusta ME and east of the Appalachian Mountains.
CONDITION ALPHA means that WXRISK.COM thinks a K-U / highly ranked NESIS ( KU= Kocin and Uccellini case book of 36 Major NE US snowstorms and NESIS = Northeast Snowstorm Index Scale) event is about to Occur. Weather Hobbyists… out of control News Media… Professional Meteorologists… Businesses that can be affected by Major weather events and the General Public should be aware that something Major and very serious is about to happen because of Major or recording breaking Winter storm. .
SITUATIONAL ANALYSIS :
The midday weather models continue to show a historic snowstorm coming for much of Virginia as well as a Northwest North Carolina and the Maryland Eastern shore… possibly reaching into the DC metro area as well. As we continue to get closer and closer to the event the weather models are actually increasing the snow amounts!
This has a high probability event of placing in the top 10 heaviest snowstorms of all time for the Richmond metro-area and possibly record shattering snow for locations such as Roanoke Lynchburg Danville Charlottesville Fredericksburg and Warrenton. Perhaps the biggest shift in the models here today is the potential that the 850 Low is going to turn north or track to the north of Hatteras and closer to the southeast Virginia coast. The 12z December 17 European model run has a 980mb Low early Saturday morning parked off of walls file and by about 100 miles… and this is closely supported by the 12z CMC and 12z Ukmet runs as well. The European and Canadian model QPF amounts is impressive and appear to be increasing as event gets closer and closer.
The model trends today with all of the primary forecast models such as the 12z CMC Ukmet and ECMWF has shifted North. All Models take the surface and 850 Low further to the north but these Models do so AFTER the 850 Low has reached Cape Hatteras . In essence the track at that point is almost due north at 72 or 73 west Longitude. This accounts for these exceptionally heavy precipitation forecasts over Virginia northern North Carolina and Maryland.
As I have stated several times in Condition Charlie #1 and Condition Bravo #2 and in various postings here a SV… in order to get this major coastal storm to track further to the north something HAS to displace OR remove the impressive talled PV that is trapped by the Greenland block over New Brunswick Canada. ANY model solution which attempts to lift the Low up and off shore of the middle Atlantic coast but does not move the PV out of the way ….is synoptically unsound and should not to be given any consideration.
The best case of this model disconnect from reality can be seen with the 12/17 18z run of the WRF solution which manages to close off a impressive deep 500 low over southern New Jersey at 54 hrs. If such an event were to happen then of course be the surface Low and 850 Low would the track thru eastern MN and over southeast VA. This in turn would lead to massive reductions in the snow amounts over southern New Jersey the Lower Maryland Eastern shore and Eastern Virginia.
That being said it needs be kept in mind over the last six days not a single model of any kind… at any point… has developed a deep closed 500 Low over southern New Jersey early Saturday morning. This includes over 12 runs of the European model and European ensembles… over 12 runs of the Ukmet and CMC … and 22+ runs of the operational GFS and GFS ensemble.
So you will have to excuse me if I believe that the 18Z WRF is suspect.
I have kept the New York City and the NYC metropolitan areas and CT and RI as well as Boston out of the HECS area for these reasons. These areas will still see significant snow (SECS event threshold will be reached). In addition due to the colder temperatures there snow ratios will probably be 13 :1 or 15:1 . There will still be a extremely sharp cut off the snow shield to the north and west of Washington, DC Baltimore Philadelphia and over Northern NJ and NYC.
DETAILED ANALYSIS
1. The event itself is a classic text book MILLER A event and develops as a PJ (Polar Jet) short wave Phases with the short wave in the STJ (subtropical Jet) over the Delta and Gulf coast region..
2. NAO phase — severely Negative with huge multi contoured 500 mb Ridge over Greenland that extends west into Labrador. This is arguably one of the best and idealized –NAO / East coast set ups in the past 40 years.
3. 50/50 LOW — IDEAL. Even though the large powerful and very deep PV that is situated over New Brunswick Canada is NOT a 50/50 Low …it is in effect ” acting” in this synoptic sense as if it was a large 50-50 Low. The position of this feature over southeastern Canada insures that the confluence own than the Polar Jet has set up across central New England which is significantly idealized or textbook KU set up for northeast US snowstorms.
4. PV feature; Intense and displaced well to the south. The displacement of the PV into northern Maine and far southeastern Canada is a significant synoptic development and is often a precursor that skill the medium-range forecast is look for in forecasting the possible development of the major East Coast snowstorm. The reason for this is that it becomes impossible to keep and sustain the PV this far to the south unless something else is going on in the atmosphere… something significant which in this case counts as the REX Block -NAO over Greenland.
5. 850 LOW TRACK: over ILM and between HSE and ECG … then turning to the NE and crossing 70 west Long Line at 38N.
Weather models are NOW and Only just Now – showing a slight SHIFT in the track of the surface Low and the 850 Low Once these Low reach Cape Hatteras. Thus Northern VA DC Metro area intro central MD and BWI metro regions are now in the Heavy snow Band.
This 850 Low track now does match several of the 33 – Now 35 — KU snowstorms.
6. SPLIT FLOW CYCLOGENESIS .
http://1664596.sites…clogtypes/3.jpg
7. ANALOG at 500 MB to this event:
JAN 23-24 1940
JAN 27-29 1922 (the Knickerbocker storm)
And to a lessor degree
JAN 1-3 1980…. FEB 5-7 1980 and MARCH 1-3 1980… but of course this event will be somewhat warmer at 850 and surface levels.
WHAT CAN GO WRONG
It must be kept in mind that figuring out “What could go wrong…” I am not basing it as to how much snow could fall in your backyard . The focus is with respect to the forecast scenario I have laid out here in this CONDITION BRAVO statement.
Keeping that in mind …there are several things watch out for. The first is that the 850 low could track significantly further to the north either cutting through southeastern Virginia or simply climbing up the coast offshore and crossing 70 west longitude at say 38 North. This would place much of the Northeast in the heavy snow bad especially over coastal locations but even while inland ould see significant snow in this possible scenario.
This would be greatly enhanced as a likely possibility… if the PV does in split into two portions.. and then the western portion of the PV does retrograde to the Great Lakes… THEN does need in the phasing of the PJ and STJ. This would pull the Surface Low closer to the coast and allow the 850 Low track further to the north.
12/19/09 0900 est
SET CONDITION BRAVO #2 …. SET CONDITION BRAVO #2
WXRISK.COM has issued CONDITION BRAVO #2 effective for the approximate time from 0100 12/19/ 2009 to 2000 EST 12/20/2009 for the Likely occurrence of a M.E.C.S. (Major East Coast Snowstorm) Event or H.E.C.S. (Historic East Coast Snowstorm) for the Following areas of concern:
… Eastern third of TN …
… NC west of I-85 and NORTH of I-40 (Henderson – Durham – Greensboro- Winston Salem Hickory Ashville) …
… All of VA even Hampton Roads…
… All of M except for western 2 counties of MD…
… All of DE except for far northwest portion…
… All of MD… except for far western MD…
… All of DE…
… All of southeast PA…
… Southern NJ and eastern Long Island…
… Southeast Mass and RI …including BOS…
at this time CONDITION BRAVO #2 does NOT include Southeast NY… NYC… northern NJ… western LI.. or CT.
CONDITION BRAVO shall by declare whenever the atmospheric pattern and Model data has shift into a much more favorable state for SECS event (or Higher such as a MECS or HECS)…. to occur over a given period or a specific Location along the East Coast of the CONUS from Atlanta GA to Augusta ME and east of the Appalachian Mountains.
CONDITION BRAVO represents a paradigm shift by WXRISK.COM from Potential of a Threat — CONDITION CHARLIE– to a THREAT regarding East coast snowstorm development. Meteorologist …Weather Hobbyists… and the General Public need to know a serious MILLER A/ Southern Stream coastal Low will likely develop and this event become High Ranked on the NESIS snowstorm scale event and a KU candidate during the time period of listed above.
SITUATIONAL ANALYSIS :
The overall model data and tendency remained very consistent — again discounting the wretched operational GFS over the last two days— with no significant northward trend at all with respect to the track of the surface Low. What we have been seeing over the last 12 to 18 hours is a significant expansion of the precipitation shield on the northern and northwestern quadrants as the models see the service-level stronger and deeper with each run. That however is not truly a shift to the north since the actual track of the surface Low is what determines if there is a track adjustment to be made.
So far the models have shown remarkable consistency over the last 48 hours— provided of course one discounts the wretched GFS which only today finally got a clue. Right Now I am operating on this CRITICAL PREMISE: the track of the actual surface Low passes over or very close to Cape Hatteras or probably just to the south… then heads ENE… crossing 70 W Longitude at 37-38 North . This has been the trend on the European and Canadian models for several days and only today did we see the wretched GFS finally pick up on this.
WHAT ABOUT THE 18Z WRF/ GFS run of DEC 16?
As impressive as the 18z WRF and GFS are I cannot in good conscience right now forecast 22 inches of snow for central Virginia. I have never been a fan of the 6z or 18z Models and have consistently argued that they very existence is a waste of time and money by NCEP. Be that as it may… It needs to be kept in mind that as ONLY24 hours ago several runs of the operational GFS as well as some of the ensembles forecasted no significant snow or rain of any kind over the northeast quadrant of the US right through to December 31.
The 18z GFS QPF ensemble does however seem very reasonable. The potential still exist for the system to be pulled north by 100 or 200 miles… but that is dependent upon the PV — polar vortex – over New Brunswick Canada splitting into two portions with the Western portions sliding towards the Great Lakes. I mention this possibility at SV on DEC 14… and discussed it in great detail in the CONDITION CHARLIE #2 statement.
This scenario still remains a viable threat as of this issuance of this CONDITION BRAVO statement.
Such a shift to the North would place the heavy snow into DC and into BWI PHL and NYC/ western Long Island and possibly coastal CT. This possibility was discussed in the CONDITION CHARLIE #2 statement. At this time however given the inherent unreliability of the 18z Models… the overall synoptic pattern and the fact that the threshold for significant snow in these areas is higher than it is for central and southern VA NC… and MD… I cannot include these areas in the threat to see MECS / HECS snowfall. That may change.
It is still possible these areas could however see significant snow (S.E.C.S.) but that is still undecided.
DETAILED ANALYSIS
1. The event itself is a classic text book MILLER A event and develops as a PJ (Polar Jet) short wave Phases with the short wave in the STJ (subtropical Jet) over the Delta and Gulf coast region..
2 NAO phase — severely Negative with huge multi contoured 500 mb Ridge over Greenland that extends west into Labrador. This is arguably one of the best and idealized –NAO / East coast set ups in the past 40 years.
3. 50/50 LOW — IDEAL. Even though the large powerful and very deep PV that is situated over New Brunswick Canada is NOT a 50/50 Low …it is in effect ” acting” in this synoptic sense as if it was a large 50-50 Low. The position of this feature over southeastern Canada insures that the confluence own than the Polar Jet has set up across central New England which is significantly idealized or textbook KU set up for northeast US snowstorms.
4. PV feature; Intense and displaced well to the South. The displacement of the PV into northern Maine and far southeastern Canada is a significant synoptic development and is often a precursor that skill the medium-range forecast is look for in forecasting the possible development of the major East Coast snowstorm. The reason for this is that it becomes impossible to keep and sustain the PV this far to the south unless something else is going on in the atmosphere… something significant which in this case counts as the REX Blockmn -NAO over Greenland.
5. 850 LOW TRACK: over ILM and HSE crossing 70 west Long Line at 37N . Weather models can throw out as much precipitation and graphics as they want to but this sort of track with the 850 low passing south and east of Hatteras is NOT GOOD for those who want to forecast heavy snow in the big cities in the Northeast from DC to Boston. This track of the 850 Low as shown by all of the models today– has absolutely no matches whatsoever with any of the 33 – Now 35 — KU snowstorms..
Indeed this track closely matches the great miss snowstorm of February 22 — 24,1989… and closely matches the major snowstorms of JAN 1940 JAN 1-3 1980…. FEB 5-7 1980 and MARCH 1-3 1980. Indeed in order for me to shift the CONDITION BRAVO threat into the big cities of the Northeast the models going to have to significantly change the track of the 850 Low so it ends of crossing the 70 W Long closer to 38 or 40 N ( i.e. “the Benchmark”) .
6. SPLIT FLOW CYCLOGENESIS that is Progressive .
http://1664596.sites…clogtypes/3.jpg
6. ANALOG at 500 MB to this event: JAN 1940 JAN 1-3 1980…. FEB 5-7 1980 and MARCH 1-3 1980… but of course this event will be somewhat warmer
at 850 and surface levels.
WHAT CAN GO WRONG
It must be kept in mind that figuring out “What could go wrong…” I am not basing it as to how much snow could fall in your backyard . The focus is with respect to the forecast scenario I have laid out here in this CONDITION BRAVO statement.
Keeping that in mind …there are several things watch out for. The first is that the 850 low could track significantly further to the north either cutting through southeastern Virginia or simply climbing up the coast offshore and crossing 70 west longitude at say 38 North. This would place much of the Northeast in the heavy snow bad especially over coastal locations but even while inland ould see significant snow in this possible scenario.
This would be greatly enhanced as a likely possibility… if the PV does in split into two portions.. and then the western portion of the PV does retrograde to the Great Lakes… THEN does need in the phasing of the PJ and STJ. This would pull the Surface Low closer to the coast and allow the 850 Low track further to the north.
======================================================
DEC 15 2009 2300 EST
SET CONDITION CHARLIE …. SET CONDITION CHARLIE EVENT #2
WWCINC — Weather Weenie Commander in Chief — has issued CONDITION CHARLIE advisory #1 effective for the approximate time of 12/18/09 to 12/20/09 for the POETENTIAL of a M.E.C.S. (Significant East Coast Snowstorm) Event or H.E.C.S. (Historic East Coast Snowstorm)
Condition CHARLIE refers to a change in the synoptic overall pattern across North America that is more “favorable” for the development a S.E.C.S. (Significant East Coast Snowstorm) event .. or event of greater Magnitude such
as a M.E.C.S. (Major East Coast Snowstorm) or H.E.C.S. (Historic East Coast
Snowstorm)
Keep in that a CONDITION CHARLIE is NOT a forecast. Instead this statement is a Notice that some sort of significant winter threat could be developing.
The areas of concern … based upon the latest data… is:
… Eastern two thirds of TN …
… Eastern Two thirds of TN…
… Northern GA including ATL Metro area…
… All of NC…
… All of VA except for far northwest portion…
… All of MD… except for far western MD…
…. All of DE…
… All of southeast PA…
… Southern NJ and eastern Long Island…
… Southeast Mass and RI …including BOS…
SITUATIONAL ANALYSIS :
Most of the medium and long-range weather models have been focusing on this potential event since about December 4 -5. I waited until about December 7 or 8 before I started to jump on this potential event. I did hesitate for two reasons. First the ECMWF GFS and CMC on DEC 7 came out with a potential significant snowstorm for today December 15: the scenario called for the cold front now moving into the East Coast to have swept off the East coast then stall over GA where Low pressure would develop and bring the snowstorm as the Low moved up the coast. Instead the cold front was delayed and there is no going to be no significant development on the southern end of the front.
The second reason I delayed was I want to ensure that in fact we did have a REX block in place over eastern Canada and Greenland. A REX block formation is often a significant development and can be ….with other factors of course …quite favorable for seeing a major East Coast snowstorm. However by December 7 — 8 I became convinced that the development of the Rex block on all the ensemble that was in fact going to occur. T us even though the December 15 — 16 event fell apart I remained very bullish on the overall pattern.
The Rex block is directly connected to the development of the intense PV — polar vortex — over New Brunswick Canada and southeastern Canada in general. The vortex is massive and extends back into the western Great Lakes and upper Mississippi Valley as well as extending east past of funneling into the Northwest Atlantic.
As a general synoptic rule…. the bigger the Ridge in the REX BLOCK the buger the 500 Low ” under” the 500 mb Ridge. In this particular case this rule is proving to be exactly correct with a mass of the ridge over Greenland and a huge vortex over southeastern Canada.
There have been many instances of a suppressed or displaced PV over Maine/ New Brunswick which have lifted out to the north in time for a southern Low to travel up and off the East Coast and bring a major or historic snowstorm to the middle Atlantic states and New England. The KU – Kocin and Uccellini case books of 36 Major NE US snowstorms and NESIS (Northeast snowstorm Index Scale) history is replete with numerous examples of this occurring. But in all cases where such a pattern has developed and we have seen a major snowstorm for the Northeast… the suppressed or displaced PV over southeastern Canada eventually GETS OUT OF THE WAY IN SOME MANNER.
Sometimes the vortex slides towards Newfoundland where it becomes the infamous 50-50 Low. Sometimes the vortex splits into two pieces which can actually aid in the process of phasing between the PJ and STJ …IF the western PV slides west towards the Great Lakes — as we saw in JAN 29-31 1966.
However as long as the PV stays over New Brunswick and does not get out of the way or break apart… than what we end up with is a large cyclonic flow covering much of the eastern half or eastern third of the US into the western Atlantic Ocean. In such a pattern ANY Low pressure area that develops along Gulf Coast or southeast can only track in a ENE direction off the southeast coast and probably passing south of Bermuda.
Indeed this is what many of the models were shown earlier in the week with regard to the potential for system on December 18 — 19.
It is a basic but often forgotten rule of meteorology in the medium-range forecasting genre that as we get closer to the event models agreement should be increasing in their depiction of the event…. intensity and track as well as overall synoptic features. As I stated above we did not see that with the December 15-6 threat.
This event however is a totally different kettle of fish and as we get closer to December 18-19 there is increasing model agreement. Not prefect but increasing. This is a significant trend even from 120 and 132 hrs out.
The changes started yesterday when the 12z Dec 14 ECMWF expanded the PV and implied a second center developing over the Great Lakes day 4-5-6.
This trend continued with the 0z DEC 15 CMC and ECMWF runs where both models split the PV apart into two distinct features with the western portion of the vortex retrograding into the Great Lakes. This allows the northern branch or the PJ to drop into the s/w (short wave) in the STJ… in other words to “PHASE ” better and sharper.
In doing so this causes the Low pressure area that formed over Southern George or northern Florida to track closer to the coast and become a major coastal system with the European and Canadian models eventually developing the system down to 972 mb by the time it crossed or reach the 70° west longitude parallel.
As I have stated elsewhere the only way for this Low to has a chance of developing and coming up the coast –even if only partially is if the massive PV over southeastern Canada/ New Brunswick gets out of the way or splits apart. If that does not happen — even though right now many the models are showing this sort of development — there will be no significant storm for the East Coast… be it NC or MASS.
Another important aspect of this has to do with the overall flow. Even if we do get to distinct separating PV centers… the development of two of these centers still means the overall flow is still going to be WSW – ENE. We are not going to see a massive trough or a strong s/w come up the coast in this pattern.
Thus the other key aspect is particular event will be the placement of the actual surface Low. Many of the models earlier in the week were placing the Low in the central Gulf of Mexico then tracking it through central Florida and then well out to sea. As of late many the models now have the system forming over the Gulf coast then tracking too closer to Jacksonville …to Wilmington NC and Cape Hatteras then out to sea.
This is not really a northward trend in the classic sense…. but rather where does the initial Low pressure area form on the 18th?
Does it form south of New Orleans? Does it form over the FL Panhandle? Does attracting southern Georgia?
In every one of these instances it will be fairly easy to project the track of the system and for the short range models to handle the track of system… again because of the overall flow will only allow for a SE Low to climb only so far up the coast no matter how well-developed it may be.
In other words IF the Low tracks over Jacksonville then begins to intensify it will climbed partially up the coast – but only so far. In this pattern we are not going to see a low track from Jacksonville to Boston. Nor is it possible in this pattern to see in a land track either so that can be ruled out categorically. (That is not to say one particular model one over the next four days might show them and track but given the overall pattern I am convinced that this will not be the case and you should be too.)
