NYC/PHL December 24-27 Potential - Part 2

[earthlight]

is the northern stream disturbance the little indent in what looks to alberta at hr 54 h5?

It's not a "feature" per se...more of an entire lowering of heights. Basically the area from Central Canada to the international border back to the area North of the Lakes on the 60 hr NAM. Heights are lower across the Lakes/Central US as a result of increased involvement if you compare to the 00z run. I guess if you had to pick one main "feature" it would be the shortwave coming over the top of the ridge near the International Border at 60 hrs that's driving this whole thing.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/06/images/nam_500_060s.gif

[tombo82685]

It's not a "feature" per se...more of an entire lowering of heights. Basically the area from Central Canada to the international border back to the area North of the Lakes on the 60 hr NAM. Heights are lower across the Lakes/Central US as a result of increased involvement if you compare to the 00z run. I guess if you had to pick one main "feature" it would be the shortwave coming over the top of the ridge near the International Border at 60 hrs that's driving this whole thing.

http://www.nco.ncep....am_500_060s.gif

ok i see what your saying now.

[A-L-E-X]

The big thing is the northern stream now. We've got a developing consensus that this shortwave is going to track much slower than the GFS was indicating. Now we need the northern stream involvement. Compared to it's 00z run, and the 00z GFS, the NAM has more northern stream involvement.

Keep in mind that the northern stream energy is very poorly sampled at the moment. Long way to go.

Yeah Cisco is going with the OP EURO and the NAM looks to be trended that way. We could have an old fashioned E/E consensus on our hands!

BTW most of our local forecasters are going with the EURO as well and most have thrown out the possibility of any snow on XMAS and are going with a Sunday and Monday event.

[Rtd208]

With all the hot air we have around here you really won't need that. lol

i would just rent a plane and stall it over the air in northern canada, that should blow her pretty far south and fast.

[tombo82685]

john look at how eerily similiar the 6z nam is compared to the 0z euro at h5 with hgt lines, pretty scary

[earthlight]

john look at how eerily similiar the 6z nam is compared to the 0z euro at h5 with hgt lines, pretty scary

PM me an image if it's from vista..my computer can't load their site right now.

[GD0815]

PM me an image if it's from vista..my computer can't load their site right now.

a lil off-topic but do you sleep? if so, when?

[earthlight]

a lil off-topic but do you sleep? if so, when?

Hoping to sleep soon

[tombo82685]

Hoping to sleep soon

alright i pm'ed u the image

[GD0815]

Hoping to sleep soon

welll we definitely appreciate you and tombo helping our late night threads here!

[SnowGoose69]

I've gotta figure as of now the best way to forecast it is a miss for NYC and western LI...this solely based on the assumption the GFS is too fast and the NAM/Euro are likely to slow...in other words move everything near or slightly east of the GEM...the good news is we have ALOT OF TIME still before we can go either way...this storm IF it happens may not drop a flake before 12:00am on the 26th...who would have guessed that 2-3 days ago?

[bass28]

not sure what to think about the 6z nam?close but not fully like the euro but good jump to it,john and tombo you guys think they look like thattt much?

[tombo82685]

here is the ggem 12z ens mean compared to 0z ggem ens mean

12z

0z

[CooL]

That is kind of odd tombo, considering the 00z ggem op went east yet the ens went west from 12z when the ens were east and the op was west...haha thats confusing

[psuhoffman]

not sure what to think about the 6z nam?close but not fully like the euro but good jump to it,john and tombo you guys think they look like thattt much?

its similar in all ways except one, but I think its the key. Euro still has a healthy STJ vort in the gulf at 90 hrs. The 84 hour 6z NAM is losing the southern energy again in favor of the northern stream energy phasing in. When the phasing happens on the euro its into the southern stream, not northern dominated. The other models...all of them, are squashing the southern stream energy in favor of the northern stream. I think this is the difference. If the phasing happens down in the gulf, everything digs more and there is a sharper turn up the coast. If the northern stream dominates, that energy is still racing SE and so it takes a wider turn and OTS. Not sure at this stage how to examine which is depicted correctly.

[SnowGoose69]

I'm not a big GEM fan overall but I think its really damn close right now to what eventually is going to occur...with the hope its 75-100 miles too far east.

[tombo82685]

That is kind of odd tombo, considering the 00z ggem op went east yet the ens went west from 12z when the ens were east and the op was west...haha thats confusing

yea you would of thought the other way around like you said. Looking at that 0z map, there are probably a few that show a good hit for i95

[baroclinic_instability]

It is amazing, when you look at this,http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ir_enhanced+/24h/, that the models can even suggest such an event this far out.

That said, 6Z NAM looks mostly good and has a good push of CAA towards the GOM with the secondary S/W over Ark/MO, but the total lack of a low level cyclonic circulation seems a bit odd.

[psuhoffman]

I'm not a big GEM fan overall but I think its really damn close right now to what eventually is going to occur...with the hope its 75-100 miles too far east.

I think philly needs more then 75 miles

[tombo82685]

It is amazing, when you look at this,http://www.atmos.was..._enhanced+/24h/, that the models can even suggest such an event this far out.

That said, 6Z NAM looks mostly good and has a good push of CAA towards the GOM with the secondary S/W over Ark/MO, but the total lack of a low level cyclonic circulation seems a bit odd.

when you keep saying the caa, im assuming your meaning cold air advection? Are you saying that the stronger that push the better chance of inducing a cyclogenisis. If so how do you determine that on a map if the caa is stronger or not?

[baroclinic_instability]

its similar in all ways except one, but I think its the key. Euro still has a healthy STJ vort in the gulf at 90 hrs. The 84 hour 6z NAM is losing the southern energy again in favor of the northern stream energy phasing in. When the phasing happens on the euro its into the southern stream, not northern dominated. The other models...all of them, are squashing the southern stream energy in favor of the northern stream. I think this is the difference. If the phasing happens down in the gulf, everything digs more and there is a sharper turn up the coast. If the northern stream dominates, that energy is still racing SE and so it takes a wider turn and OTS. Not sure at this stage how to examine which is depicted correctly.

Yes, mostly agree. I still won't budge from my initial assessment that the PV phasing with the northern stream is the key. Why? Low level CAA decreasing with height results in upper level height falls. Simple dynamic meteorology there. The CAA in the low levels needs to beeline towards the GOM to establish a strong baro zone plus develop the upper level trough into/near the GOM. GFS early runs sucked and took the initial phase and incited strong enough cyclogenesis to change the trajectory of CAA towards the east coast instead of the GOM...hence the northern solution. What would be ideal is a phase with the weak southern PV that actually increases the low level CAA towards the GOM which then deepens the trough.

[baroclinic_instability]

when you keep saying the caa, im assuming your meaning cold air advection? Are you saying that the stronger that push the better chance of inducing a cyclogenisis. If so how do you determine that on a map if the caa is stronger or not?

Ha, good timing. Read my reply to PSUHoff

[tombo82685]

Ha, good timing. Read my reply to PSUHoff

so basically what your saying is that you would want an amplified neutral based trof over the gom region, since that would drive the caa do south to that region where the h5 low is. This would then induce the cyclogenesis with the baroclinic zone of the warm gom waters and the caa. The low pressure strengthens, neg tilt, and the h5 low from ohio valley gets pulled to the low somewhere to caputure it? yay or nay? Lol im not a met guy like john, just love tracking stuff, more of a hobby, im a turf guy lol.

[baroclinic_instability]

Let me illustrate. Two days ago, the 0Z GFS was trying to show a sufficiently strong phase with the southern PV to incite strong enough cyclogenesis to alter the cold air advection in the low levels eastward:

Compare to tonights run at the same verificvation time:

What is the difference. The early run GFS was trying to phase the PV, which it had much stronger, then incite cyclogenesis. This cyclogenesis changed the track of the CAA eastward and resulted in a trough that developed much farther N.

How?

QG Theory explains it real easy.

The circled term is "differential temperature advection". This is the height tendency equation. It tells us how upper level heights will react. In this case, we are looking at the partial derivative of thermal advection with respect to height. In other words, how does thermal advection change with height. In this case, if we have strong low level cold air advection decreasing with height, upper level heights will fall.

[tmagan]

In terms of CAA (or CAD), if you look at the MSLP 1000-500 mb map, you see the isobars and thicknesses plotted there. When you see the isobars and thicknesses make a box (or solenoid), you have cold, or warm air advection, depending on where the winds are going following the isobars around either low or high pressure. If you have northerly winds, and lower thicknesses to the north, and you have the isobars and thicknesses make a closed box, you have cold air advection. The key is the smaller the box, the stronger the advection.

Edit: I hate the fact that 'advection' is flagged by spell check.

[tombo82685]

Let me illustrate. Two days ago, the 0Z GFS was trying to show a sufficiently strong phase with the southern PV to incite strong enough cyclogenesis to alter the cold air advection in the low levels eastward:

Compare to tonights run at the same verificvation time:

What is the difference. The early run GFS was trying to phase the PV, which it had much stronger, then incite cyclogenesis. This cyclogenesis changed the track of the CAA eastward and resulted in a trough that developed much farther N.

How?

QG Theory explains it real easy.

The circled term is "differential temperature advection". This is the height tendency equation. It tells us how upper level heights will react. In this case, we are looking at the partial derivative of thermal advection with respect to height. In other words, how does thermal advection change with height. In this case, if we have strong low level cold air advection decreasing with height, upper level heights will fall.

ahhh, so when you get the upper level hgts that fall this induces cyclogenesis?

[A-L-E-X]

I've gotta figure as of now the best way to forecast it is a miss for NYC and western LI...this solely based on the assumption the GFS is too fast and the NAM/Euro are likely to slow...in other words move everything near or slightly east of the GEM...the good news is we have ALOT OF TIME still before we can go either way...this storm IF it happens may not drop a flake before 12:00am on the 26th...who would have guessed that 2-3 days ago?

It depends on what is meant by miss SG-- regardless of what happens with the coastal, we should get 2-4" at least, no?

[A-L-E-X]

Yes, mostly agree. I still won't budge from my initial assessment that the PV phasing with the northern stream is the key. Why? Low level CAA decreasing with height results in upper level height falls. Simple dynamic meteorology there. The CAA in the low levels needs to beeline towards the GOM to establish a strong baro zone plus develop the upper level trough into/near the GOM. GFS early runs sucked and took the initial phase and incited strong enough cyclogenesis to change the trajectory of CAA towards the east coast instead of the GOM...hence the northern solution. What would be ideal is a phase with the weak southern PV that actually increases the low level CAA towards the GOM which then deepens the trough.

I remember the discussion from HPC which mentioned this. Basically, height differential thermal advection is the key to the phase and timing.

[baroclinic_instability]

Let me illustrate. Two days ago, the 0Z GFS was trying to show a sufficiently strong phase with the southern PV to incite strong enough cyclogenesis to alter the cold air advection in the low levels eastward:

Compare to tonights run at the same verificvation time:

What is the difference. The early run GFS was trying to phase the PV, which it had much stronger, then incite cyclogenesis. This cyclogenesis changed the track of the CAA eastward and resulted in a trough that developed much farther N.

How?

QG Theory explains it real easy.

The circled term is "differential temperature advection". This is the height tendency equation. It tells us how upper level heights will react. In this case, we are looking at the partial derivative of thermal advection with respect to height. In other words, how does thermal advection change with height. In this case, if we have strong low level cold air advection decreasing with height, upper level heights will fall.

Let me continue.

What do I mean when I refer to incipient cyclogenesis?

Incipient cyclogenesis develops when an atmospheric disturbance develops over a baroclinic zone in the low levels. Mass divergence in the upper levels will incite low level convergence (this requires the level of non-divergence to be in between) since the atmosphere follows the laws of mass continuity. In other words, mass can not be destroyed or created. Upper level mass divergence incites incipient cyclogenesis over the baroclinic zone and cyclogenesis begins. Note in the early GFS runs this cyclogenesis altered the cold air advection pattern towards the East Coast as it developed a strong low level circulation (see above pictures). As I showed above, if the low level trajectory of the CAA is shifted eastward, where does the trough develop? Towards the EC, and the overall track is much farther N.

What we want is a PV that incites weak lower level cyclogenesis...just enough to enhance the low level cold air advection towards the GOM but not enough to shift it eastward before our trough develops and digs farther S.

[A-L-E-X]

Let me continue.

What do I mean when I refer to incipient cyclogenesis?

Incipient cyclogenesis develops when an atmospheric disturbance develops over a baroclinic zone in the low levels. Mass divergence i the upper levels will incite low level convergence (this requires the level of non-divergence to be in between) since the atmosphere follows the laws of mass continuity. In other words, mass can not be destroyed or created. Upper level mass divergence incites incipient cyclogenesis over the baroclinic zone and cyclogenesis begins. Note in the early GFS runs this cyclogenesis altered the cold air advection pattern towards the East Coast as it developed a strong low level circulation (see above pictures). As I showed above, if the low level trajectory of the CAA is shifted eastward, where does the trough develop? Towards the EC, and the overall track is much farther N.

What we want is a PV that incites weak lower level cyclogenesis...just enough to enhance the low level cold air advection towards the GOM but not enough to shift it eastward before our trough develops and digs farther S.

IOW it's all a matter of timing, and rather fine timing at that lol. BTW I love your use of the law of conservation of mass, but would just add that it can be converted to energy (which mass is just another form of.) Perhaps cyclogenesis includes a partial conversion also, which happens in many chemical and physical processes (though not to the extent that it happens in nuclear reactions.)

Wonderful educational discussion, Im very glad I stayed up for this