1515 EST 19 JAN
This whole event for the weekend is turning out vastly different from what I thought was going to happen over the past weekend– that is to say JAN 15-16. Recall or read read the post below from a afternoon of the 16th the the scenario which I was considering was that the cold front which sweeps through the east coast first…. on JAN 20… then when the front stalled a second piece of energy would interact along the front … and develop a second larger coastal Low for at least some portion of the Middle Atlantic Coast and possibly into New England JAN 22-23.
Since that posting obviously a whole lot of data has come out and this scenario is no longer viable. The first change has to do with the cold front. It still going to come through on the 20th or 21st but the the Low pressure area is going to develop on the cold front BEFORE or just as the front is reaching the the Middle Atlantic states. This greatly reduces the chance if seeing ANY accumulating snow over Central … southwest and eastern Virginia.
Another reason is that ahead of the cold front we have a pretty mild air mass. Temperatures have surged into the 50s across the Middle Atlantic states this afternoon… (which oddly enough is exactly what I have been forecasting from last week to my private clients even though the GFS MOS guidance only supported temperatures in the lower to Midddle 40s.) With SW winds coming in a head of the cold front tomorrow and mild temperatures currently in place any precipitation is going to fall over Central Virginia will be rain which might and as wet snow.
Now once the surface Low begins to rapidly develop it will pull in colder air so that the mixture of rain / snow over the Washington, DC area were quickly change over to snow in Northern Virginia as well as DCA and into Baltimore. If the cold air gets into the Northern VA DCA the metro area in time …a few inches of snow could fall.
It is important to keep in mind that this is a fast moving cold front and the Low pressure area is going to zip rapidly through the East coast. This is one of the reasons why I am not forecasting significant snow amounts over the big cities of I95 from Philadelphia to Boston. Another main reason has to do with the storm track. I am not sure if the Low was going to pass close enough to those I-95 big cities or develop into a significant system that drives heavy snow into Philly NYC Northern NJ CT and Boston (Not NO snow… heavy snow … over 6″).
Beyond this event the models continue to show a strong piece of energy into southern Jet stream that is going to develop a significant coastal Low over Georgia on January 22. So in that regard the European model has gotten at least some of the general features of the pattern correct. We can see the significant Low pressure area off the southeast coast here. It is THIS feature that the models were focusing on last weekend for a possible significant East coast winter storm.
What is killing the second storm– the Low off the GA coast on JAN 22 —from coming up the coast is a another piece of energy in the Jet stream that is diving SE from the central Rockies chords the lower Plains. In the old days this feature would be called “a kicker” because it drives the main piece of energy the or shortwave over the Georgia Coast EAST and out to sea.
Taking a look at the larger picture one of the reasons perhaps the primary reason why the big storm scenario for JAN 22-23 which the models were forecasting on January 15-16… is not going to verify has to do with the overall pattern which is change significantly in the past seven days.
The High latitude blocking over Eastern Canada and Greenland is no longer there. And NO model data of any kind on the Morning or afternoon cycles shows any hint of this feature coming back before the end the month. This has a profound impact on the overall pattern. In some of the the weather forms which are out there on the Internet you will come across some Ignorant weenie tried to argue that we don’t need to have high latitude blocking in place for east coast snowstorm patterns.
Not only is that not true but the Ignorant weenies deliberately distort the premise into something which is not relevant. The research and data is clear that at the time of the Noreaster hitting the East coast we do not have to have a block over Greenland Eastern Canada – known as the -NAO. The issue is getting the pattern to set up so that the coastal low becomes a snowstorm and NOT a rain storm or Midwest storm.
The high latitude blocking which develops over Canada and eastern Greenland the -NAO… affects the pattern in many different ways when one is considering the potential for East coast winter storm.
In the days leading up to a possible East coast winter storm… the blocking often causes Low pressure areas over southeast Canada to get “trapped” over or close to the New Foundland Canada. This feature in the weather business is referred to as a NF LOW or a 50/50 Low….(50° N latitude 50° W longitude ). The combination of the blocking feature over Eastern Canada and Greenland and the 50/50 Low means that the large cold arctic High which settles in over the Great Lakes and /or New England stays in position and is not able to slide off the coast. This means that the cold air stays in place over the northeast from North Carolina to Maine .
Without the blocking features over Canada and without the 50/50 Low the cold High pressure ares do not stay in postion long enough to ensure an all snow event for the coastal Plains — from Raleigh to Boston). Now obviously the impact of the large cold High in position is much more important for locations such as Raleigh NC and Richmond VA than it is for Boston and New England.
We can see the impact of this with the next potential event on January 25 – 26. Looking at the weather maps initially on January 24 25 from the various weather models it would seem to be ideal or pretty close to ideal for a significant East coast winter storm to occur.
However all the models showed that the large cold High slides off the coast rapidly once the coastal low begins to develop. Why does this happen? There is NO 50/50 Low and No Blocking over eastern Canada and / or Greeland so there is No actual mechanism in the atmosphere to keep the cold High in place over the Great Lakes/ southern Canada and or northern New England.
But even besides all that… the blocking patterns are what good meteorologists look at to see if the pattern is ” setting up” for East coast winter storms has further implications.
The jet stream maps from the various global weather models such as the European the Canadian and the GFS all show at the surface low on January 25 it is going to come inland and track along the coast or very close to it.
Some of you may already be wondering if it is possible that this Low could be shift its track to the East a couple of Hundred miles? This is where the blocking patterns that we look for come into play because IF we had those features in existence over Eastern Canada and Greenland… that any shift to the east would be favored.
Instead what we have is the merging or Phasing of the Two Pieces of energy into one BIG trough over the Midwest because of the lack of Blocking .
If we had the blocking over Eastern Canada and Greenland then this phasing of the 2 pieces of energy would occur East of the Mississippi river and this in turn would favor the coastal Low on JAN 25-26 tracking more to the east and thus increasing the chances of late all snow event.
But since we don’t have any that blocking —the phasing between the two pieces of energy — occurs of much sooner ( WEST of the Mississippi River) which is the kiss of death sign for those wanting were or hoping for an all snow event on the East Coast.
Looking out to day 10 we see some HINTS that a New MIGHT be forming over Iceland and the UK. WE can clearly see significant heights building in the Jet stream. often… but not alwways… when this happens the Block will retogreade into Greenland. So far NONE of the 11-15 day ensemble are showing this.
1955 EST JAN 16
Well it’s time to start talking about the next significant winter threat for the East coast. And by that I am not talking about the the January 18 event since that is a whole bunch of nothing. Sure the precipitation still might start off as snow from PHL to Boston but it IS going to change over to rain on southeasterly winds… low level warming temperatures both at the surface and all the way to 850 mb. Now some of you may look at the surface map from our morning or tomorrow evening and see this large cold High centered over southeastern Canada and wonder why or how can the cold air possibly not hold in place as the southern Low comes up the coast.
The first reason is that we don’t have any feature over southeastern Canada to cause the the cold High to slowdown. So it is going to keep on moving rapidly to the east. But in addition the event on Tuesday is going to consist of two areas of Low pressure– one over the Great Lakes and the southern Low (which we can see the heavy showers and thunderstorms over the delta region this evening). It is the “attack” of both of these Lows which will help rapidly wrote the cold air just as the precipitation begins to move surge northward. 850 MB temps will warm to +3c or warmer even over eastern and southern New England. In addition if you look at the RH (relative humidity) fields on the walk short range weather models you will notice that there is large gaps in the precipitation coverage over VA MD and south central PA.
The main issue of concern and focused from MY which really is on the THREAT of significant winter storm threat for JAN 21-22-23.
THREAT… not yet a fact or a forecast
Once again we have the European models which had been the most bullish and aggressive on this feature and have shown the coastal development of some type on the cold front for the past 7 runs. And not surprisingly the operational GFS has been showing no such event of any kind –until early this morning and midday today. And the Canadian model has been hinting at some sort of system developing on the cold front over the southeastern states since Saturday.
Essentially what we are looking at are two possible scenarios. The new strong cold front will drive through the Midwest into the Middle Atlantic states on January 20. The front should drive fairly deep into the Tennessee Valley and the southeastern states by the morning of the 21st. Arctic High pressure will move into position over Montreal.
At that point some sort of wave of Low pressure will develop on the front over the southeast states. The interaction between the large cold High to the north and this Low will set the stage for a classic cold air damming event.
This image will show you what a COLD AIR DAMMING event looks like on the weather maps and weather models.
We can see the the numerous thick Black Lines over VC NC MD PA NJ having this funny bend of ” kink” in them. The appearance of CAD is often but not always a sign of a significant winter storm developing but it does not tell us which areas could see the the significant snow and ice . Many years ago weather models consistently over warmed the atmosphere at low levels during East coast storms and would prematurely forecast a changeover from snow to rain. However once the the phenomenon known as CAD was identified …meterologists were able to see this very clearly and the winter forecasts became a lot better when it ame to winter storms along the East coast.
THE BIG EAST COAST STORM SCENARIO:
The last few runs of the regular or operational European model has been developing Low pressure over Georgia… which moves to Eastern North Carolina on JAN 22 then undergoes rapid intensification as a tracks off the southeast coast of New England. In this sort of scenario the model has heavy ice over northeast GA western SC much of NC and snow from VA to southern Maine — including the big cities of the I 95 corridor.
The FLAT WAVE SCENARIO is supported by most of the other model data including the European ensemble . In this set up a wet but rather flat looking Low pressure area develops over the southeastern states and then tracks ENE off the North Carolina Coast out to sea.
The following Models support this scenario.
12Z SUNDAY CANADIAN
12Z SUNDAY GFS
12S SUNDAY BRITISH/ UKMET
In this particular scenario only North Carolina and Virginia would see significant snow and ice. The precipitation would probably start off as ICE then changeover to snow and probably no significant snow from DC northward.
Given the number of big storms which is hammered the Northeast US this winter it is easy to assume that the big East coast winter storm scenrio #1 is probably going to turn out to be orrect . And of course given the seasonal trend it’s hard to argue against that the BIG East coast winter storm idea. But if we decide to use science as opposed to weenie wishcasting… the last 3 big East coast winter storms have all occured with strong High latitude blocking over Eastern Canada and Greenland (a strong negative phase of the NAO) . That is clearly not going to be the case this time around and certainly not by January 20-21-22.
On the other hand if we do end up getting the flat wave of Low pressure scenario then there COULD be a problem with that northern extent of the precipitation. We could end up seeing significant snow and ice storm over NC and only the southern half VA…. with very little winter precipitation falling north of Fredericksburg.
Right now I do not have a particular favorite— I am not biased towards one scenario or another one. The change in the pattern in the jet stream over the Eastern Canada and Greenland should be significant in my opinion so as to favor the flatter weaker way of scenario affecting only the Virginia North Carolina this coming weekend .
But on the other hand it sure is hard to ignore the seasonal trend which has been for big snow storms and the northeast US.