East Coast Storm Development

[WhiteFox]

Ok, so I figured it would be interesting to track this developing feature right up to final solution if I get the time. At the moment it is a long way out and could either go too far out to sea, track inland, or simply not phase and give a damp squib solution.

To start with, what do we require for a SECS (Significant East Coast Storm) or higher? What is the definition?

Actually, there are no definitive measurement scales such as for Tornadoes or Hurricanes. Several analyses have been performed on the development of such storms and therefore categorised, Miller-A and Miller-B being two such examples, but in terms of impact the closest we have is the Nort East Snow Impact Scale (NESIS) which attempts to measure the total snowfall in inches and weights it by population affected. Therefore, a storm dumping 30 inches in Maine and 2 inches in Boston will have a lower impact than 15 inches in Boston and 5 inches in Maine for instance. See this link for some analysis.

In terms of ingredients we obviously need cold air. Usually this will require a high pressure pumping colder air to the south. Looking ahead to this weekend, we see a high pressure in place providing the cool air:

The cold air is not as intense as we’d like it to be, but it is in the right place. This is important because of something called Cold Air Damming (CAD). This is where cold air becomes trapped East of the Appalachian Mountains. This can sometimes be seen on maps where the isobars are noticeably kinked. The chart below from just before the President’s Day Storm II clearly shows CAD in effect; notice the kink in the isobars as the low pressure pushes up against the Canadian high pressure over Quebec:

The storm shown in the above charts eventually produced 20 inches+ over large areas. The CAD was important because it meant that the warmer air wrapping around the low pressure was not able to overcome the cold air already in place so the PPN remained all snow. See this excellent case-study for a full description of the PDII storm.

The CAD is not so evident in this weekend’s charts. It is not essential for the production of a major storm, but without strong CAD there is the likelihood of snow turning to sleet, freezing rain or even plain rain as warmer air pushes in around the system. This is what happened during the two big storms last year; the Valentine’s Day storm and the St. Patrick’s Day storm which both produced a few inches of snow followed by freezing rain. Further inland however, the PPN stays as all snow or snow to sleet.

The forecasts keep changing on this system as we would expect at this stage. YOu can see by looking at the charts below just how thin a line there is between a bullseye snowstorm and a rain event.

Firstly, look at the current forecast track on the SLP chart. The first chart shows T+108:

On this chart we can see that the wind for NYC has a SE component. This means at this stage that rain is the most likely outcome. This is backed up by the 850 temperatures on which I've given a rough position for NYC. The position is extremely marginal because as you can see, the temperature gradient is extremely high; literally 20 miles makes all the difference:

At the surface this translates to a freezing line perilously close to NYC. Take a drive over the George Washington Bridge and head about 10 miles North and you'd be below freezing:

The same is true of dewpoints. Again the 0oC line is just on the mainland:

And finally, thickness. We're looking for the 540 line which is generally accepted as the rain/snow line. Any higher and the cold air is too shallow to support frozen PPN:

Once again we are just on the edge!

So, on today's 18z forecast NYC just misses out on the worst (or best!) of the snow. The exact track of this storm will move around bit over the next few days; the worst thing that can happen for us is an inland runner where we end up on the Eastern side of the storm in heavy rain...

[WhiteFox]

The GFS ensemble mean for the 18z shows a big hit for the NYC area and the rest of the NE coast:

For some reason the Operational run continues to show the track to be to the West of the other ensemble members.

A lot depends on the track of a storm which will pass across the area into Thursday. At the moment it looks like Upstate New York and New England will see a fair fall of snow from this system. As per the weekend system, NYC is right on the line once again:

The timing and exact track of this system will have a large impact on where the weekend's storm goes. For this reason we cannot even begin to look at more precise forecasts until Friday, and even then the rain/snow line won't be pinned down until right on the event. There will be a lot of nowcasting going on from Saturday night onwards...

[WhiteFox]

Graphic showing PPN distribution for Thursday's storm:

At the moment TWC is forecasting that the snow will turn to rain overnight; NWS discussions are calling for sleet to rain for the big cities based on GFS projections. The NAM forecast of a more southerly tracking low is being discarded, but there are few dissenters on the weatherboards (amongst the Mets) over here:

AS FOR THE THE DEVELOPMENT AND POSITION OF THE ASSOCIATED LOW...THE

NAM HAS TRENDED FARTHER SOUTH AND COLDER OVER THE PAST FEW RUNS. IN

FACT...IT NO LONGER HAS ANY ABOVE FREEZING LEVELS ALOFT OVER THE CWA

DURING TIMES OF PRECIP. GIVEN THE UPPER FLOW PATTERN...I THINK THE

NAM`S DEVELOPMENT OF THE LOW OVER TENNESSEE / NORTH CAROLINA IS TOO

FAR SOUTH. THE GFS HAS BEEN MORE CONSISTENT OVER THE PAST FEW RUNS

WITH A BROAD LOW PRESSURE CENTER DEVELOPING FARTHER NORTH IN THE

OHIO VALLEY BEFORE EVENTUALLY MOVING THROUGH THE VICINITY OF 40/70

BENCHMARK FRIDAY NIGHT. ALSO PREFER GFS PRECIP TIMING AS NAM HAS

GENERALLY BEEN TOO SLOW THIS SEASON. PRECIP CHANCES BEGIN MOST

LIKELY DURING THE LATE MORNING TO MIDDAY PERIOD AS IT SPREADS WEST

TO EAST ALONG WITH ISENTROPIC LIFT. BY THURSDAY NIGHT...EASTERN

ZONES LIKELY SEEING PRECIP...WITH CATEGORICAL POPS WEST.

WITH THE EXPECTED FARTHER NORTH TRACK...PRECIPITATION TYPE WILL

TRICKY AS ELEVATED WARMS LAYERS WILL BE PRESENT. THE PAST COUPLE OF

GFS RUNS SHOW THIS LAYER TO BE AT 850-800 MB DURING THE

MORNING...AND 800-750 MB IN THE AFTERNOON. ATTM I DON`T THINK ANY

ELEVATED LAYERS WILL WARM UP ENOUGH FOR FREEZING RAIN TO OCCUR.

SLEET WILL HOWEVER KNOCK DOWN SNOW ACCUMULATIONS TO A DEGREE.

CONFIDENCE IN FINE DETAILS IS STILL LOW...BUT GENERALLY EXPECTING

MAINLY SNOW AND SLEET INLAND WITH ADVISORY CRITERIA SNOWFALL

AMOUNTS. SINCE THIS WOULD BE LATE IN THE 4TH PERIOD...WILL HOLD OFF

ON THE ADVISORY AND UPDATE THE HWO. COASTAL SECTIONS (EXCEPT SE CT

COAST) WILL SEE PRIMARILY RAIN WITH SOME SLEET...AND LITTLE IN THE

WAY OF SNOWFALL. THE SUBURBS IMMEDIATELY NORTH AND WEST OF THE CITY

LOOKS TO BE MORE OF AN EVEN SNOW...SLEET AND RAIN MIX.

For the weekend, the discussion is no longer about whether there will be a storm (I should have kept copies of discussions earlier in the week; along the lines of 'models projecting a possible storm but confidence not high' as you'd pretty much expect), but over the track of the storm and PPN types:

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...

MAIN CONCERN DURING THE EXTENDED PERIOD IS THE POTENTIAL FOR A MAJOR

WINTER STORM ON SUNDAY. ALL GLOBAL MODELS HAVE BEEN CONVERGING

TOWARDS THE ECMWF OVER THE LAST 24 HOURS...WHICH IS WHAT HPC IS

GOING WITH IN THEIR FORECAST...SO WILL FOLLOW SUIT IN THE DATABASE.

ONE ISSUE IS THAT THE SFC LOW HAS SHIFTED FURTHER NORTH ON THE

11/00Z RUN AS COMPARED TO THE 10/12Z RUN WHICH MOVES THE LOW OVER OR

JUST SOUTH OF LONG ISLAND. THIS WOULD SUGGEST A HEAVY RAIN

EVENT...EVEN FOR INLAND ZONES. HIGH PRESSURE IS IN A PRIME LOCATION

FOR OPTIMAL COLD AIR DAMMING WHICH COULD SPELL TROUBLE FOR AT LEAST

AREAS AWAY FROM THE IMMEDIATE COAST AT THE ONSET. 11/12Z ECMWF JUST

CAME IN AND HAS SHIFTED THE TRACK BACK TO THE SOUTH...SIMILAR TO

10/12Z RUN.

THE REMAINDER OF THE GLOBAL MODELS TRACK THE LOW TO THE SOUTH OF

LONG ISLAND WHICH WOULD MEAN A COLDER SOLUTION...HOWEVER WITH THE

CONVERGENCE TOWARDS THE EC...DO NOT FEEL CONFIDENT WITH ANY ONE

SOLUTION AT THIS POINT. WILL STICK WITH A RAIN OR SNOW FORECAST ATTM

WITH HOPE THAT THINGS WILL COME INTO BETTER AGREEMENT AND BE MORE

CONSISTENT OVER THE NEXT FEW DAYS.

OTHERWISE...HIGH PRESSURE BUILDING IN TO THE NORTH FRI NIGHT THROUGH

SAT WILL PROVIDE FAIR AND DRY WEATHER CONDITIONS WITH ONLY AN

INCREASE OF MID AND HIGH LEVEL CLOUDS DURING THE DAY SAT.

BEHIND THE STORM...A TIGHT GRADIENT WILL REMAIN ACROSS THE AREA INTO

MONDAY AS HIGH PRESSURE BUILDS IN FROM THE NORTH...BUT IT SHOULD BE

DRY MON AND TUE.

TEMPS WILL GENERALLY BE BELOW NORMAL DURING THIS TIME.

On TWC just now Jim Cantore (definitely the best Met they have) showed the three possible tracks and highlighted the favourite as being the coastal track, but only just!

[Roger J Smith]

Looks like a disorganized mess with the Great Lakes primary never really absorbing the coastal storm, just phasing with it, and so the arctic front will tend to run right along the coast, sleety mix for most heavily populated areas, freezing rain inland in some cases, 2-5 inches of snow over some higher ground. Great Lakes system has a slight warm sector that will just introduce 1-2 C air and turn wet snow to drizzle.

This is quite a weak storm by coastal standards, but sometimes these cause a lot of havoc because of the widespread slick roads, not enough snow to close them entirely so traffic is only partly reduced, however unable to drive at more than 30 mph, so gridlock develops. Been there, done that.

[WhiteFox]

Looks like a disorganized mess with the Great Lakes primary never really absorbing the coastal storm, just phasing with it, and so the arctic front will tend to run right along the coast, sleety mix for most heavily populated areas, freezing rain inland in some cases, 2-5 inches of snow over some higher ground. Great Lakes system has a slight warm sector that will just introduce 1-2 C air and turn wet snow to drizzle.

This is quite a weak storm by coastal standards, but sometimes these cause a lot of havoc because of the widespread slick roads, not enough snow to close them entirely so traffic is only partly reduced, however unable to drive at more than 30 mph, so gridlock develops. Been there, done that.

Indeed it does look likely to be more defrosted that frozen for the coastal plain, but there is the potential for a fair bit of liquid further inland. Compared to last year the interior North East is buried in snow... Still a good chance of early snow to rain even towards the coast. Of course, there is still the possibility of the storm tracking further out (although the trend hasn't been good). We won't know for sure until Saturday; no Mets are calling this one yet for sure!

Taken from NYNJPAWeather on Eastern US Weather Forums:

Another interesting storm begins to take shape over the Gulf Coast. Low pressure system that form in the Gulf Coast spell trouble, period. These type of storms have no lack of precipitation nor energy to work from. The low pressure system usually bring with it the power of convective latent heat release from the Gulf of Mexico, the additional moisture source of the tropical Atlantic, and the ability to drive a strong thermal gradient from 850 mb down to the surface. These type of storms have two types of storm tracks. One track goes from the Gulf of Mexico to the St. Lawrence Valley. This type of track is a result of a phase of the northern and southern branch of the Jet Stream. The storm tracks in land as the dominant 500 mb low sits over the Great Lakes. The other track, which almost all models except the GFS has, keeps the jet streams unphased and sends the storm from the Gulf of Mexico to the Delmarva coast and off towards the “bench mark”, which is defined as the perfect track for a snow storm for the major cities of the Northeast and northern Mid Atlantic. Now, there is a lot that can go wrong here for this storm. The clipper to the north supplying the fresh, new cold air may be too slow. The Gulf low may travel too far north and phase, thus a rain storm. The track of the low, even towards the coast, could be too far out or too close to the coast. Right now, there are many question to answer and not enough data to answer them. However, it is clear there is a high storm potential for this period. Who gets what, I have no idea, but everyone should get something.

Edited December 12, 2007 by WhiteFox

[WhiteFox]

Looks like a disorganized mess with the Great Lakes primary never really absorbing the coastal storm, just phasing with it,

Could be prescient words Roger!

We've gone from a perfect benchmark coastal track, to an inland runner dishing out aome leading edge snow and rain, to the latest NAM forecast which ejects the storm straight East off the coast and misses everyhwere North of DC altogether!

The NAM model simply doesn't phase at all:

The problem with this storm was always the lack of some of the factors which would support the storm. We were relying too much on the phasing which was always a long shot. Anyway, the chase is not yet over by any means. The GFS still progged a decent storm at 18z, albeit rather wetter than I'd like. If the GFS and ECM somehow figure out a compromise with the NAM then you never know...

Having said that, it is early in the season yet for a full-blown Nor'Easter anyway. This time last year we couldn't buy a flake of snow, yet tomorrow there's a good chance of at least a couple of inches.

[WhiteFox]

We're now at the stage where we should be seeing pretty good agreement in the models; the storm is about 48 hours away. Are we seeing this agreement? No!

Let's look at the model forecasts:

UKMET:

The UKMET takes the storm inland bringing warm air and rain to the whole of the East Coast. The reason for this is the high pressure to the North; earlier in the run, cold air damming forces the storm further West, then the High pressure over Canada starts to shift East. This is because there is nothing to the East to prevent this happening such as a deep low pressure over Newfoundland.

GFS:

The GFS takes the primary low up towards Ohio before the energy quickly transfers to the Coast. Take a look at the two charts immediately following:

The main problem is that the 850 Low does not move far enough East quickly enough to prevent any changeover. Looking at the corresponding 850 chart for t+54 we see warm air being advected very quickly up the coast:

Then, as you can see, at the same time the low pressure is re-forming off the Carolinas, the 850 low remains to the West of New York City:

So by this stage we are looking at rain for New York. Of course, this is assuming that the cold air below is shifted out of the way so easily. During both the Valetine's Day Storm and the March storm last year, the colder air at the surface proved very difficult to shift, so we found a changeover from snow to sleet to freezing rain. Having said that, the cold last year was much deeper to start with because of the time of year, and the sea temperatures were colder, so a change to plain rain seems likely. By the time the 850 low moves out to sea and draws in the colder air from the North, the PPN is all but over.

Judging by the GFS tonight, it's a snow to sleet to freezing rain to rain event. Probably quite a bit of PPN overall and parts of upstate New York and Northern New England could well be buried by this!

The ECM takes the system inland and then bombs off the coast of Maine.

The forecast isn't nailed yet, but the favourite at the moment seems to be an inland track with the possibility of redevelopment just out to see. The key things to watch on Saturday will be how quickly the transfer takes place. Not all is lost, but at the moment it's looking wet after a white start...

[Roger J Smith]

Well, my apologies, but on my first reading of the thread I somehow thought we were talking about Thursday's rather weak system (which had been quite a heavy freezing rain producer in the southern plains earlier). So my comments really had nothing to do with the weekend storm at all.

As far as that goes, it does look like a complex winter storm for all areas inland from the coastal plain, trying to lift warm air north but probably meeting with a lot of resistance as the Pacific system coming inland pushes the central high far enough southeast to deflect the low off a track towards Lake Ontario and push it more east across New York City into the Long Island region. With this, I would expect NYC itself to start with sleet, turn over to rain at about 4-7 C with SE winds, then turn back to sleet and finish off with a dusting of snow on Sunday evening. Further inland, quite heavy amounts of snow and freezing rain or ice pellets are likely over almost all of New England, NY state, southern ON, parts of PA and OH, s MI etc. The most snow from this would likely be 10-15 inches across the Adirondacks into Vermont and New Hampshire, as well as isolated 10 inch amounts where E-NE winds come ashore from the lower Great Lakes, such as Toledo OH.

NYC could get quite a heavy rainfall from this, in the order of 2 to 3 inches, I would say, as well as much of NJ and the PHL area. Could produce some severe weather also as the cold front tracks through the Carolinas and southern VA on Saturday night into Sunday.

Do I have the right storm now?

[WhiteFox]

Well, my apologies, but on my first reading of the thread I somehow thought we were talking about Thursday's rather weak system (which had been quite a heavy freezing rain producer in the southern plains earlier). So my comments really had nothing to do with the weekend storm at all.

As far as that goes, it does look like a complex winter storm for all areas inland from the coastal plain, trying to lift warm air north but probably meeting with a lot of resistance as the Pacific system coming inland pushes the central high far enough southeast to deflect the low off a track towards Lake Ontario and push it more east across New York City into the Long Island region. With this, I would expect NYC itself to start with sleet, turn over to rain at about 4-7 C with SE winds, then turn back to sleet and finish off with a dusting of snow on Sunday evening. Further inland, quite heavy amounts of snow and freezing rain or ice pellets are likely over almost all of New England, NY state, southern ON, parts of PA and OH, s MI etc. The most snow from this would likely be 10-15 inches across the Adirondacks into Vermont and New Hampshire, as well as isolated 10 inch amounts where E-NE winds come ashore from the lower Great Lakes, such as Toledo OH.

NYC could get quite a heavy rainfall from this, in the order of 2 to 3 inches, I would say, as well as much of NJ and the PHL area. Could produce some severe weather also as the cold front tracks through the Carolinas and southern VA on Saturday night into Sunday.

Do I have the right storm now?

Darn tootin'!

I'm actually impressed that I managed to call close to your forecast given that it's my first stab and you have many years of experience in these parts!

Some frozen initially then fairly quickly to rain seems almost certain for New York City right now. There is some good news though: the latest GFS progs a lot of rain for the South East. They really desperately need it down there so I'd happily give up a snowstorm for the greater good (well, it is Christmas!).

Any views on the pattern going forward Roger? I know most Mets were going for a strong warm up for the middle of December (in fact, everyone's favourite ramper Joe laminate floori cancelled winter for after the middle of December) but at the moment the warmer conditions keep getting pushed back. What has surprised me is just how long the cold has held in the MidWest and just how intense it has been. Close to record lows in parts of the High Plains at times! Could this winter have a surprise in store for us?

Anyway, I'll sign off for the night with the forecast snow depth map for North America on Monday. If anyone wants to move somewhere where you get a lot of snow, then take your pick!

[lightnin]

wow cool info its a shame i cant add to that how strong will it be??

[WhiteFox]

wow cool info its a shame i cant add to that how strong will it be??

Current GFS progs a 980MB system just over Boston by Sunday evening; pretty strong especially as it'll be drawing very cold NW winds in by that stage (although just about all the PPN will be done for NYC by then).

The cold air is already in place; tomorrow sees a high of around freezing for New York. Should make it feel seasonal whiilst I'm doing my shopping! After that it's a Saturday of observing for me. It's the first chance I've had to watch a developing coastal storm when I'm actually at home (I was away on business for both last year's affairs).

[Rollo]

I have just been skyped by a cousin in providence who te,ls me they had 11" of snow last night and are programmed to have between 1 and 2 feet on the Nor'easter at the weekend.

[Roger J Smith]

The very latest 48h regional seems to show this storm making more northward progress over the weekend, could push the rain-snow line well north of both NYC and Providence into northern New England and far upstate NY, although I haven't seen the Sunday evening or Monday morning positions on this latest run, they aren't generated yet and I am out the door.

But based on the track change so far I would say the low is heading for southern Quebec now and the heavier snow will be shifted well north into Michigan and central Ontario, southern Quebec and the higher peaks of New England only.

And it could therefore get as warm as 10-15 C on Sunday in NYC as the subtropical air looks poised to run as far north as central NJ now.

Coastal redevelopment may not take place now until Monday afternoon near Nova Scotia or the low may just keep moving across the Gulf of St Lawrence.

[johnholmes]

nice to see that at th eastern end of a major continent there is doubt over something expected no more than 48 hours away!

kind of makes it easier to deal with some of the comments on our model thread.

[BLAST FROM THE PAST]

The very latest 48h regional seems to show this storm making more northward progress over the weekend, could push the rain-snow line well north of both NYC and Providence into northern New England and far upstate NY, although I haven't seen the Sunday evening or Monday morning positions on this latest run, they aren't generated yet and I am out the door.

But based on the track change so far I would say the low is heading for southern Quebec now and the heavier snow will be shifted well north into Michigan and central Ontario, southern Quebec and the higher peaks of New England only.

And it could therefore get as warm as 10-15 C on Sunday in NYC as the subtropical air looks poised to run as far north as central NJ now.

Coastal redevelopment may not take place now until Monday afternoon near Nova Scotia or the low may just keep moving across the Gulf of St Lawrence.

Roger

That in itself could allow the HP retrograde over us to be more pronounced. Interesting Model discussion to say the least...any chance of popping in and giving your thoughts? Big JH has been peeved by a couple of, yes, stupid posts is fair to say Incredible NA weather...sure has rocked Joe B I reckon. Oh just in case I don't know how the Ice Storms and colder than expected weather will affect my Yuletide greetings

BFTP

Edited December 14, 2007 by BLAST FROM THE PAST

[Roger J Smith]

I'll update the forecast later, but just in case night owls are about while I'm having dinner, this system didn't really change all that much, the track jogged a little north on the morning 12z run and then returned out towards the former track after 60h.

I've noticed in the past that fairly large storms that occur near warming episodes usually go through this northward shift on model runs until they settle into the more accurate inland track that will probably prevail here.

As to the influence this might have on the blocking European high, I would say not that much, because eventually that high is probably going to fade away and allow the mild SW flow to return, so a few miles difference in the track of a 980 mb low near 80 W will all come out in the wash with regard to that larger shift.

Probably the east coast is now about to see a warming trend in general, after this storm and a slight drop in temps early next week, I would expect the flow to re-set into the predicted east coast ridge and central trough, and that might lock in for much of the winter, making it a rather mild winter in general for eastern and south central regions, and a cold one in general further west and north.

[WhiteFox]

The very latest 48h regional seems to show this storm making more northward progress over the weekend, could push the rain-snow line well north of both NYC and Providence into northern New England and far upstate NY, although I haven't seen the Sunday evening or Monday morning positions on this latest run, they aren't generated yet and I am out the door.

But based on the track change so far I would say the low is heading for southern Quebec now and the heavier snow will be shifted well north into Michigan and central Ontario, southern Quebec and the higher peaks of New England only.

And it could therefore get as warm as 10-15 C on Sunday in NYC as the subtropical air looks poised to run as far north as central NJ now.

Coastal redevelopment may not take place now until Monday afternoon near Nova Scotia or the low may just keep moving across the Gulf of St Lawrence.

I think your forecast of double figures would probably verify if the 850 low does not transfer East fairly sharpish. As it is the 0z brings the low in over the centre of Ohio at 36hours, but transfers to NE New York by 48 hours drawing in the colder air. Given the shortish time span of the warmest air (GFS progs a max of about +7oc) and the heavy PPN it looks being that most miserable of things: cold with heavy rain and winds.

The current track of the system looks to give us some light snow to start, quickly turning to sleet and then rain as the upper level system is in about the worst place for cold air.

The peak of the warmth at 850 comes at 18z, which translates to 1pm Eastern, so temperatures will probably rise quite a bit. Having said that, I think about 7oC is a fair shout given the conditions and the wrap-around of cold air arriving later.

We shall see!

As for looking ahead, it does seem that winter is locked in for the Upper Midwest and High Plains at the moment. Looks like being quite a bit below average for December up there. For the East, the La Nina pattern should spell a fairly mild winter according to most models and Mets, but we shall see. It already seems that JB cancelled winter too early; he's been wrong often enough in the past so time will tell.

For once I'm actually reasonably happy the storm won't be as bad as originally progged; I fly back to the UK on Monday for Christmas and it would have been very inconvenient timing!

[Roger J Smith]

This storm now firmly on the inland track, currently developing near Natchez MS, heading for about Pittsurgh before making any sort of eastward turn. Rollo, you can let your cousins know they are now looking at a brief snowfall all melting on Sunday in a heavy rain (I am sure they've heard already). Latest prediction from me for JFK, 12 C briefly but the warmer air moves just offshore and might clip southeast MA on Sunday evening, but a large zone of transitional temps 7-10 C with heavy rain looks like the main impact for the urban northeast. Heavy snowfall now likely to run Chicago to central MI and Georgian Bay portions of ON into southern Quebec, eventually Quebec City and north could see 50 cms. Debs if you happen to read this, expect a heavy mixture of snow, freezing rain and sleet tonight and Sunday morning, turning to a heavy rain on Sunday night, temps warming to 6 C, then a blast of much colder weather on Monday once the low moves past, as it is deepening towards 960 mbs and will drag down some -15 C air towards New Brunswick by Tuesday.

[WhiteFox]

Looks very messy out there at the moment.

Hopefully some rain for the South East.

Still the calm before the storm here in New York; sunny and cold with a few thin high clouds starting to appear.

[Nick F]

Noticed DTrisk has posted a snow threat map for the NE US on his site:

http://www.wxrisk.com/1STCALL.jpg

[WhiteFox]

Noticed DTrisk has posted a snow threat map for the NE US on his site:

http://www.wxrisk.com/1STCALL.jpg

Definitely not an easy forecast to make even with the storm bearing down on the areas involved!

A good soaking rain for New York anyway. Currently 1oC here with a dewpoint of -14oC; even if any frozen ppn made it this fair it would probable be virga anyway...

[Jan 87]

If the storm is further inland than expected then presumably it will hit further to west of Greenland, and so better for us down the line?

[WhiteFox]

If the storm is further inland than expected then presumably it will hit further to west of Greenland, and so better for us down the line?

The primary low you are seeing at the moment will eventually die down as some of the energy transfers to the coast. Another Low should re-form over the coast at some stage over the next 24 hours and this is the one which will eventually provide the East Coast with its PPN. The track of this has been forecast to be a coast hugger for the past couple of days so nothing completely unexpected so far....

Also, look at what is starting to happen off the coast of South Carolina:

Once this starts to get organised and the 850 low starts to shunt East as the High pressure over Canada gives way we should see this feature start to take over. For a perfect Nor'Easter with snow, we'd need to see the High over Canada hold firm and the upper low to track further East. As it is too much warm air is drawn up and the Low tracks too close to the coast placing us in the warmer air.

Latest observations from Central Park:

Time Wind Vis Weather Sky Temp DP Pressure

14:51 Vrbl 5 10.00 Fair CLR 32 5 30.46 1030.8

Edited December 15, 2007 by WhiteFox

[Yozzer]

Recently bought ourselves a holiday home in Northern New Hampshire, Dalton in South Coos County. Temp there at present -14, dew point -21.

Looking at the current situation, I think too much faith is being vested in the models bringing the storm too far west. I feel things may change quickly overnight so the area at most risk is shunted very slightly further east, away from west /central Quebec and into eastern Quebec and northern New England (but not the immediate coast). The reason is I think the temperature gradients are steeper than the models are currently showing, allowing a rapid deepening of the storm slightly further east than currently progged, but I would be pleased to hear of any thoughts on this.

ps, I have asked our caretaker guy to turn up the heating to keep the snow from building up on the roof!!

[WhiteFox]

Looking at the current situation, I think too much faith is being vested in the models bringing the storm too far west. I feel things may change quickly overnight so the area at most risk is shunted very slightly further east, away from west /central Quebec and into eastern Quebec and northern New England (but not the immediate coast). The reason is I think the temperature gradients are steeper than the models are currently showing, allowing a rapid deepening of the storm slightly further east than currently progged, but I would be pleased to hear of any thoughts on this.

I think that is unlikely. At best the secondary low may track a bit further East. The Canadian High has nothing to stop it exiting stage right so the primary low will continue to the West.

As for temps, there may be longer periods of freezing PPN in some places further East, but I can't see areas in Southern New England and Boston southward not changing over to plain rain. Southern NH may also see some freezing rain for a while.