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Wintry January 3rd-6th, 2018 Winter Storm The ARCC/Xtreme Weather Special

As verification nears, we're slowly losing the spurious relative vorticity lobes off the SE US coast and the low-mid level vorticity max over the central Gulf Coast and Louisiana is getting more intense.

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Webberweather53 said:
As verification nears, we're slowly losing the spurious relative vorticity lobes off the SE US coast and the low-mid level vorticity max over the central Gulf Coast and Louisiana is getting more intense.

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And that my friend, as you know, is going to help us a bunch. That's why, if it continues the trend I think we could possibly see at least a weak low pop in the GOM first, thoughts?
 
A nice cluster of ensemble members west of the mean low. I think the trend will continue and one of the more westward lows will be more likely to verify.
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deltadog03 said:
And that my friend, as you know, is going to help us a bunch. That's why, if it continues the trend I think we could possibly see at least a weak low pop in the GOM first, thoughts?
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Yep I think that's very legitimate and at the very least this weak low could compete with the other low pressure center developing off the east coast of FL and tug the entire barycentre of the larger-scale low further west if it becomes more intense, for now it shouldn't be the primary feature of interest but is worth watching if this trend continues in NWP
 
Webberweather53 said:
Yep I think that's very legitimate and at the very least this weak low could compete with the other low pressure center developing off the east coast of FL and tug the entire barycentre of the larger-scale low further west if it becomes more intense, for now it shouldn't be the primary feature of interest but is worth watching if this trend continues in NWP
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Great points. That will pull the boundary closer to off shore and the main low should ride along that.
 
What will be steering the direction of the surface low once it forms? As @GaWx was mentioning, a couple of the models were steering it more in a northern direction while the majority have it going more easterly. That would make a huge difference for the Triangle region for sure.
 
These systems are so unpredictable, prime example my area Florence, SC was just placed under a Winter Weather Advisory. Did not expect that, all that being said. Winter Weather in the South can and will throw you some curve balls, whether good or bad.

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packfan98 said:
What will be steering the direction of the surface low once it forms? As @GaWx was mentioning, a couple of the models were steering it more in a northern direction while the majority have it going more easterly. That would make a huge difference for the Triangle region for sure.
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The steering direction will be dependent on the relative juxtaposition of the greatest diabatic heating within the overall low pressure gyre plus synoptic-scale flow pattern. (For example if the greatest heating was further NW towards the Carolina coast but the synoptic-scale flow favored a SSW-SW to NNE-NE propagation, the net contribution of these would be likely somewhere in between (north-ish), however would be dependent on the magnitudes of the diabatic heating produced by the convection and speed of the mid-upper level winds. The biggest implication of losing the spurious vorticity lobes off FL and seeing a shift towards a more consolidated vorticity max over the Central Gulf coast will aid in moisture transport further west into the Carolinas and could shift the primary low in the Atlantic closer to the climatologically preferred area of highest baroclinicity near the interface of the Gulf stream and adjacent cooler continental shelf waters. Akin to what we often observe in overrunning events, large, intense clusters of convection along the Gulf Coast block the northward transport of moisture into the SE US by altering local winds in the low-levels and inducing large-scale sinking in the immediate vicinity, and if we get too much convection well offshore earlier on it hurts our chances for snow by blocking low level moisture (which is why there's such a stout dry layer on the GFS). However, on the other hand, in the cases of Miller A cyclones, large clusters of Cb convection (as observed in January 2000) can aid in moisture transport in the long-run if properly placed in the flow regime (in the case of Jan 2000 it was further NW towards the NE Gulf coast), by leading to larger-scale pressure falls and generation of potential vorticity which foster synoptic-scale areas of low pressure, which, as they intensify, their wind field grows larger and more intense, thus they're capable of transporting more moisture further away from their epicenter. It's definitely a double-edged sword and situationally dependent, but the initial surge of moisture into eastern NC will probably be facilitated by this trend towards a weak Gulf low if it continues...
 
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Webberweather53 said:
The biggest implication of losing the spurious vorticity lobes off FL and seeing a shift towards a more consolidated vorticity max over the Central Gulf coast will aid in moisture transport further west into the Carolinas and could shift the primary low in the Atlantic closer to the climatologically preferred area of highest baroclinicity near the interface of the Gulf stream and adjacent cooler continental shelf waters. Akin to what we often observe in overrunning events, large, intense clusters of convection along the Gulf Coast block the northward transport of moisture into the SE US by altering local winds in the low-levels and inducing large-scale sinking in the immediate vicinity, and if we get too much convection well offshore earlier on it hurts our chances for snow by blocking low level moisture (which is why there's such a stout dry layer on the GFS). However, on the other hand, in the cases of Miller A cyclones, large clusters of Cb convection (as observed in January 2000) can aid in moisture transport in the long-run if properly placed in the flow regime (in the case of Jan 2000 it was further NW towards the NE Gulf coast), by leading to larger-scale pressure falls and generation of potential vorticity which foster synoptic-scale areas of low pressure, which, as they intensify, their wind field grows larger and more intense, thus they're capable of transporting more moisture further away from their epicenter. It's definitely a double-edged sword and situationally dependent, but the initial surge of moisture into eastern NC will probably be facilitated by this trend towards a weak Gulf low if it continues...
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Thanks. It does seem like there are many things pointing to a western correction with the precip shield. I was also trying to recall when there was a storm with this much phasing that went directly NE instead of more north up the coast? I'm sure it's happened.
 
Interesting read Webber and delta...not sure I’ve seen a gulf low mentioned... this thing is going to get all kinds of crazy before it gets here...
 
Good to see an old buddy from the other board, WeatherNC, is now a member here as well. He is a HUGE get. If this was the NFL draft, SouthernWX just got the #1 pick. That says something about this board...

Anyway, I tweeted this not long ago (hopefully it shows up easily on here)


Loving the trends. I don’t get to post here often as I’m busy and Twitter is really easy for quick thoughts, but I’m definitely more intrigued with this system than I was 24 hours ago. Big runs tonight!


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Jon said:
Good to see an old buddy from the other board, WeatherNC, is now a member here as well. He is a HUGE get. If this was the NFL draft, SouthernWX just got the #1 pick. That says something about this board...

Anyway, I tweeted this not long ago (hopefully it shows up easily on here)


Loving the trends. I don’t get to post here often as I’m busy and Twitter is really easy for quick thoughts, but I’m definitely more intrigued with this system than I was 24 hours ago. Big runs tonight!


Sent from my iPhone using Tapatalk
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I love reading your posts, and I agree with you 100% about @WeatherNC!
 
As i observe the discussion and learn from you guys i wanted to follow up on a point for your thoughts. If things develop for coastal SC, would the speed of the low pressure limit accumulation? NWS Charleston has a chance of snow Wednesday afternoon, but clear at night. Really enjoy learning from this forum. Thanks for the insight.
 
CHSweather said:
As i observe the discussion and learn from you guys i wanted to follow up on a point for your thoughts. If things develop for coastal SC, would the speed of the low pressure limit accumulation? NWS Charleston has a chance of snow Wednesday afternoon, but clear at night. Really enjoy learning from this forum. Thanks for the insight.
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Since there isn't blocking that low is going to be like a racecar. Might have been anyway if it bombs out even with blocking.
 
packfan98 said:
Thanks. It does seem like there are many things pointing to a western correction with the precip shield. I was also trying to recall when there was a storm with this much phasing that went directly NE instead of more north up the coast? I'm sure it's happened.
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As far as I'm aware of no, it's very difficult to do when your trough axis is negatively tilted haha. Even the Dec 1958 case which dumped all the snow over I-95 featured a positively tilted trough
 
CHSweather said:
As i observe the discussion and learn from you guys i wanted to follow up on a point for your thoughts. If things develop for coastal SC, would the speed of the low pressure limit accumulation? NWS Charleston has a chance of snow Wednesday afternoon, but clear at night. Really enjoy learning from this forum. Thanks for the insight.
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The wettest models, NAM and ICON, actually have it lasting 12-15 hours! It may not be the over 24 hours of the 12/1989 storm, but 12-15 hours would be longer than the average and could put down a lot, especially since some of those hours could be intense. Now some of this could be sleet and less likely ZR, which would cut down on the accumulation even if a big hit though the impact could actually be harder. It isn't always about the accumulation as far as impact is concern. Atlantans know that as well as anyone.
 
Webberweather53 said:
The steering direction will be dependent on the relative juxtaposition of the greatest diabatic heating within the overall low pressure gyre plus synoptic-scale flow pattern. (For example if the greatest heating was further NW towards the Carolina coast but the synoptic-scale flow favored a SSW-SW to NNE-NE propagation, the net contribution of these would be likely somewhere in between (north-ish), however would be dependent on the magnitudes of the diabatic heating produced by the convection and speed of the mid-upper level winds. The biggest implication of losing the spurious vorticity lobes off FL and seeing a shift towards a more consolidated vorticity max over the Central Gulf coast will aid in moisture transport further west into the Carolinas and could shift the primary low in the Atlantic closer to the climatologically preferred area of highest baroclinicity near the interface of the Gulf stream and adjacent cooler continental shelf waters. Akin to what we often observe in overrunning events, large, intense clusters of convection along the Gulf Coast block the northward transport of moisture into the SE US by altering local winds in the low-levels and inducing large-scale sinking in the immediate vicinity, and if we get too much convection well offshore earlier on it hurts our chances for snow by blocking low level moisture (which is why there's such a stout dry layer on the GFS). However, on the other hand, in the cases of Miller A cyclones, large clusters of Cb convection (as observed in January 2000) can aid in moisture transport in the long-run if properly placed in the flow regime (in the case of Jan 2000 it was further NW towards the NE Gulf coast), by leading to larger-scale pressure falls and generation of potential vorticity which foster synoptic-scale areas of low pressure, which, as they intensify, their wind field grows larger and more intense, thus they're capable of transporting more moisture further away from their epicenter. It's definitely a double-edged sword and situationally dependent, but the initial surge of moisture into eastern NC will probably be facilitated by this trend towards a weak Gulf low if it continues...
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I agree. It sounds like you believe this will be a "zipper low"....following the highest thermal gradient along the coastal boundary. If that is the case, then the precip shield will be 200 miles to the west of what is currently being depicted. It will all boil down to strength and not the track.
 
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1300m said:
I'm slugging through old storms myself trying to find any case where the H5 and surface pattern look like this one currently is modeled. Can't find one, because I don't think it exists, because I don't think it can happen ;)
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Yeah I guess it's not dynamically impossible if enough diabatic heating goes off to the east or northeast of the low but very unlikely to say the least esp given the well anticipated trend in the GFS to slowly degrade its spurious PV lobes east of FL and it would take an insane amount of diabatic heating to pull it off
 
Webberweather53 said:
Yep, these waves have once again closed the gap even more thru 39 hours, which argues for an earlier phase.
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Yep. The shortwave is a tad north at 45 hours, stronger yet holding back. Could get interesting...love the look. This screams early phase...more west.


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