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Wintry January 3rd-6th, 2018 Winter Storm The ARCC/Xtreme Weather Special
- Thread starter TheBatman
- Start date
9
93Storm
Guest
I looked at the 18z 12km NAM, and it appears that there is LES coming from Lake Lainer, GA, starting at 0z Mon. up until 06z Mon. Did anyone else see that?
It has shown up on modeling before, when this system looked like a bigger deal. Could be a sign of what's to come on future runs, with the intensity/rapid development of a low pressure closer to the coast.
9
93Storm
Guest
So, with the intense/rapid development of the low pressure over the southwestern Atlantic, this is what's causing the LES from Lake Lainer? Not sure if that is LES coming from Lake Lainer, but it surely does look like it.
Storm5
Member
I doubt there is any chance this ends up too close where it would make SE Georgia too warm that would imply big impacts much further to the NW and I just don’t see that . Would need a phase much sooner and we are talking much sooner not just a few hours
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Think we need to change the end of our title. Instead of ARCC/XTREME special. Needs to be the “SD Special Bring It Home”. Lol
pcbjr
Member
Larry,
I'll probably get a "warning" for this, but with all you contribute to this Board, folks across the sphere ought to be on bended knee on your behalf, praying and wishing and otherwise sending positive karma to the sky.
Good luck up there around the corner, my friend!
Best!
Phil
Last edited:
I'm not sure about that. Maybe Eric or 1300m can chime in on that.
9
93Storm
Guest
We won't really know for sure how much further the system could trend further west. It will all depend on how soon the phase will occur. More sooner the phase, the closer the system will be to the coast. I think, correct me if I'm wrong on that. Also, yes, there will be WAA to deal with if the system comes any closer to the coasts.
Webberweather53
Meteorologist
Yes, while the GEFS runs w/ a slightly coarser resolution than the operational GFS, the physics and dynamical cores for the ensemble members are almost exactly like the GFS so yes, there is likely some manifestation of this feedback issue on the GFS ensemble.
Convection (i.e. clusters of thunderstorms) through condensation (conversion of water vapor into liquid water), precipitation which transports sensible heat throughout the cloud and the surrounding area (this is because water has a high heat capacity and resists temperature change, so if water is falling through a tall cumulonimbus cloud and begins falling higher in the troposphere (lowest level of the atmosphere) in the middle of that cumulonimbus clouds, it's going to maintain it's initial temperature more effectively than the surrounding air so areas directly underneath heavy precipitation tend to cool as a result of this process of sensible heat transport)), convective downdrafts and entrainment of relatively drier air from the environment, (both of which cause cooling as some of the water in the cloud is evaporated w/ entrainment, while the downdrafts transport cooler air aloft in the mid-upper portions of the cloud to the surface that progressively warms on its way to the ground at the adiabatic lapse rate (8.5C/km) due to compressional heating as air density increases exponentially w/ decreasing height). These processes (among others like evaporation, melting, etc) including condensation, sensible heat transfer, and entrainment/convective downdrafts all contribute to larger-scale perturbations to the flow patterns around them which are important for the evolution of synoptic-scale low pressure systems like the one that's going to develop off the SE US coast early next week.
Condensation releases latent heat into the atmosphere which causes the air immediately surrounding where the condensation takes place to expand (because warmer air is less dense and therefore takes up more space than cooler air), expansional cooling then commences that attempts to offset this process which serves to keep the temperature constant within this parcel of air. Since the air expands in the vicinity of where condensation is occurring the density must decrease, and since the temperature remained constant within this parcel of air thanks to expansional cooling, the pressure must decrease in accordance w/ ideal gas law (Pressure=density*gas constant*temperature). As more condensation continues to occur in the cloud, the pressure drops even further. The pressure within and immediately surrounding the cloud then begins to fall relative to its surroundings, and thanks to the pressure gradient force wherein air tends to flow from higher towards lower pressure, these pressure perturbations caused by condensational heating within the cloud change local winds surrounding the cloud and incubating convective complex and more air rushes in. This evaporates more water from the ocean surface, and so you end up w/ a positive feedback loop where more condensation fuels stronger perturbations in the local winds, and the stronger local winds provide more fuel for the convection feed on, etc. Eventually what happens is this feedback becomes so strong that it begins to manifest and grows upscale to the synoptic level and actually begins to significantly impact the development of the larger-scale low pressure system it's embedded within because the scale of the wind field generated by the convection becomes of comparable size to the wind field associated with the larger-scale low pressure system.
For what we're concerned about in this case, the changes in the low pressure system ultimately affect how the moisture is transported in/around it, so it actually can have a substantial impact on whether we get heavy snow or not in this case. Additionally, since the convective-wind feedbacks (also more commonly known as wind-induced surface heat exchanges, and convective instability of the second kind (CISK) in the tropics) and vorticity growth that stimulates from them are both non-linear & exponential, these modeled errors in poorly simulating convection can actually increase even faster as time progresses, and result it very poor forecasts just 3-5 days in advance!
In summary, convection is associated with diabatic and latent heating, the diabatic/latent heating from convection affects the pressure and wind fields which then over time can grow upscale and even have a significant impact on the intensity, evolution, and placement of the synoptic-scale low pressure system. By the GFS having a convective feedback problem, and creating these sub-vortex scale eddies that are generated from convection by the very processes I just talked about (condensation being among the most important), it changes the track, intensity, and evolution of our low and the moisture transport within it such that any other competing low pressure centers (like the one that may form further NW within the overall envelope closer to the boundary of the Gulf Stream and cooler shelf waters) may be implicated which thus affects our forecast in determining how far inland snow will penetrate into the southeastern US. Yeah this is a lot of information to take in, but these general concepts are what forecasters (should) think about on a regular basis when constructing their forecasts, especially when we're dealing with rapid cyclogenesis/bombogenesis and the potential of heavy snow for some portion of the southeastern US...
bud006
Member
I'll gladly take a warning point for banter for this, but THIS post is the reason I follow weather as a 40-something dude with two jobs, two kids, a wife, a household, a baseball team to coach ... I can feel the emotion in these words, as I experience it every single time there is a snow threat in North Georgia.
I hope you cash in, I really, really do!! Now, back to the models!
--30--
Clem282340
Member
Can the low pressure come on shore around the coastal Carolina if the west trends continue
Cad Wedge NC
Member
Being an engineer, I could actually understand this... very interesting as well as educational. Thanks for posting this Webb.
raine1212
Member
My area bolded by me the wind chills will be bad, I can't even remember the last time it was that cold. NWS
Much colder temperatures are expected through this period as an
arctic air mass shifts slowly southeastward. The coldest day will be
Monday with highs only in the low to mid 30s. Monday night into
Tuesday morning, low temperatures will be in the teens, with wind
chill values 5 to 10 degrees. If wind chill values fall below 5
degrees, a Wind Chill Advisory will be needed. Tuesday will be a few
degrees warmer with lighter winds, but still 15 to 20 degrees colder
than normal for this time of year.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Surface high pressure weakens and upper level troughing sharpens on
Wednesday. An associated surface low pressure system expected to
develop off the Southeast Coast may result in increased moisture.
The models keep deep moisture east of the forecast area, but a tight
moisture gradient near the coast adds uncertainty to the forecast.
Followed consensus and kept precipitation chances less than 15
percent. Guidance is in good agreement keeping temperatures below
normal through the period. Expect highs in the mid 30s to lower 40s
and lows in the teens and 20s. Overnight wind chill values may dip
into the single digits and teens at times.
.
Much colder temperatures are expected through this period as an
arctic air mass shifts slowly southeastward. The coldest day will be
Monday with highs only in the low to mid 30s. Monday night into
Tuesday morning, low temperatures will be in the teens, with wind
chill values 5 to 10 degrees. If wind chill values fall below 5
degrees, a Wind Chill Advisory will be needed. Tuesday will be a few
degrees warmer with lighter winds, but still 15 to 20 degrees colder
than normal for this time of year.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Surface high pressure weakens and upper level troughing sharpens on
Wednesday. An associated surface low pressure system expected to
develop off the Southeast Coast may result in increased moisture.
The models keep deep moisture east of the forecast area, but a tight
moisture gradient near the coast adds uncertainty to the forecast.
Followed consensus and kept precipitation chances less than 15
percent. Guidance is in good agreement keeping temperatures below
normal through the period. Expect highs in the mid 30s to lower 40s
and lows in the teens and 20s. Overnight wind chill values may dip
into the single digits and teens at times.
.
GeorgiaGirl
Member
I would say what's coming is 2014 like cold, but it's not really all the way that, what's really impressive though is how long this cold period is going to last. Usually it's a quick shot then a respite but this is going to be a week straight of cold.
Webberweather53
Meteorologist
Lake effect snow is unusual over our part of the world because either the low-mid level temperatures aren't cold enough, we have insufficient synoptic-scale forcing (namely, a pressure gradient that's too weak, cyclones and surface highs tend to be stronger to our north), & particularly when contrasted against the Great Lakes, we don't have large enough bodies of water to build up adequate amounts of moisture so that we can generate clouds & snow. For lake effect snow, you want:
1) Adequate synoptic-scale forcing, i.e. a tight pressure gradient (& thus strong winds ) between corresponding areas of low and high pressure
2) At least a 50-80 kilometer wind fetch over a lake or other large body of water
3) 13C (or more) difference between the 850 hPa temperature and lake body temperature. This is nearly equivalent to the adiabatic lapse rate of 10C per km, so this is essentially an indication of instability. The greater the temperature difference between the low-levels (850 hPa in this instance) and the lake, the more instability, and thus a stronger tendency for vertical motion in the low-levels.
4) Low-level inversion height of at least 1 kilometer. Usually, w/ very intense arctic air masses, they're often strongest in the low-levels of the atmosphere (essentially because colder air sinks) and are capped by an inversion layer over top of the cold dome, so when you have a deeper arctic airmass, when the potential does exist for lake effect snow, the depth through which the atmosphere can mix and create low-topped convection is greater the deeper the arctic airmass is and vis versa.
Again, as mentioned the biggest inhibitor most often for us seeing lake effect snow around here is the fact that our low-level temperatures aren't cold enough, however they're liable to be very frigid in the wake of this monstrous low pressure system... Take note 850 temperatures in this GFS forecast are between -13 and -16C for 0z Friday, assuming the lakes aren't frozen and are probably cold (~5C ish temperature wise), this argues that we'll be safely above the 13C cut-off needed between the 850 hPa and lake temperature to potentially generate lake effect snow. Now, we may have some residual moisture spilling over the Appalachians from the Great Lakes so we may be able to get away w/ a wind fetch that's a little less than 50 kilometers, and we should have no issues w/ the inversion height of this intense arctic airmass and getting a pressure gradient between our beast offshore and the cold, Canadian high pressure center building down its wake.
850 hPa temps get even colder for NC later in the GFS run as this low departs, dipping down to about -20C, thus as long as some of our local lakes aren't frozen over given the aforementioned conditions in place and if we can get a little extra moisture from the Great Lakes, I wouldn't be surprised to see some lake effect snow off of Lake Kerr and/or maybe even Lake Jordan.
As recently as January 2014, we had Lake Effect snow in NC, a nice band developed off of Lake Kerr near the NC-VA border on the 22nd and dumped up to an inch or so of snow in portions of Nash, Wilson, & Wayne counties.
Checking the KGSO sounding at the time of this event shows indeed, with lakes that weren't frozen over (~5C or so), the -14C 850 hPa temperatures here (highlighted in yellow) were sufficient to generate lake effect snow in NC
Cary_Snow95
Member
NAM slower with lead wave out to 17
Webberweather53
Meteorologist
Yep, lol we're pretty much going back to the 12z run in the short range w/ the upper low closer to CA and s/w slower
Webberweather53
Meteorologist
Broken024
Member
Web what do you think the chances of precip making it west to clt are?