• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Severe Severe weather threat April 17-19

We had better hope the 3km NAM is wrong with it's depictions of dewpoints in the upper 60s to 70 across the Carolinas and CAPE of 2,000-3,000 across most of the area in advance of the best dynamics or else there will be a nasty severe weather outbreak of wind and tornadoes. The SIM radar at hour 60 shows individual supercells popping up in the areas with solid instability and a line also appears to be forming a bit further to the west. This could easily be a scenario where supercells pop in front and then a line of strong winds moves through with the best dynamics and shear later in the afternoon/evening hours.

CAPE at 18z Friday

3km.jpg

SIM radar 18z Friday

3km sim radar.jpg
 
NoSnowATL said:
Has the threat in Georgia diminished due to the arrival time over night?


Sent from my iPhone using Tapatalk
Click to expand...

For now I would say so, the 3km NAM has the storms weakening quite a bit by the time they make it to Georgia... But with all the dynamics involved I would still watch this one as the line could hold together better than it's showing. It appears though the highest threats will be west and east of Georgia. The Carolinas and Louisiana/MS/AL look like the target areas right now.
 
snowlover91 said:
We had better hope the 3km NAM is wrong with it's depictions of dewpoints in the upper 60s to 70 across the Carolinas and CAPE of 2,000-3,000 across most of the area in advance of the best dynamics or else there will be a nasty severe weather outbreak of wind and tornadoes. The SIM radar at hour 60 shows individual supercells popping up in the areas with solid instability and a line also appears to be forming a bit further to the west. This could easily be a scenario where supercells pop in front and then a line of strong winds moves through with the best dynamics and shear later in the afternoon/evening hours.
Click to expand...

SPC write up had a interesting tid bit....

...Synopsis and Discussion...
Deep upper trough extending along the MS Valley early Friday morning
is expected to continue eastward, maturing into a well-formed
mid-latitude cyclone centered over the southern Appalachians by the
end of the period. Very strong flow aloft will exist throughout the
base of the upper trough, with the strongest flow developing within
its eastern periphery Friday afternoon and continuing into Saturday
morning. 500-mb flow could exceed 100 kt, which is near record
values across the Carolinas and into the mid-Atlantic based on SPC
sounding climatology. In contrast to these impressive dynamics,
overall thermodynamic environment will be marginal. Given that ample
low-level moisture will be in place (i.e. dewpoints in the mid 60s
to low 70s and 100-mb mean mixing ratios over 12 g/kg), the modest
instability is largely a result of warm temperatures aloft and
consequent poor lapse rates.
 
snowlover91 said:
We had better hope the 3km NAM is wrong with it's depictions of dewpoints in the upper 60s to 70 across the Carolinas and CAPE of 2,000-3,000 across most of the area in advance of the best dynamics or else there will be a nasty severe weather outbreak of wind and tornadoes. The SIM radar at hour 60 shows individual supercells popping up in the areas with solid instability and a line also appears to be forming a bit further to the west. This could easily be a scenario where supercells pop in front and then a line of strong winds moves through with the best dynamics and shear later in the afternoon/evening hours.

CAPE at 18z Friday

View attachment 19108

SIM radar 18z Friday

View attachment 19107
Click to expand...
It's hard for me to buy the NAM's long range stability predictions. I have seen them bust high so many times. That said, the dynamic nature of the system and the wind energy upstairs raises the concern level. We'll have to see how things are looking from a completely overcast vs. broken sky standpoint as we near Friday. That will likely be the difference between spotty to numerous severe weather reports and a widespread outbreak.
 
snowlover91 said:
For now I would say so, the 3km NAM has the storms weakening quite a bit by the time they make it to Georgia... But with all the dynamics involved I would still watch this one as the line could hold together better than it's showing. It appears though the highest threats will be west and east of Georgia. The Carolinas and Louisiana/MS/AL look like the target areas right now.
Click to expand...
But wont this be occurring tomorrow night for AL which would diminish the threat ?
 
SoutheastRidge said:
But wont this be occurring tomorrow night for AL which would diminish the threat ?
Click to expand...

The storms would likely be moving through in the evening hours to early overnight which will allow them to still hold together especially with the dynamics involved. As you get further east into Georgia the models are indicating the storms moving through at the most stable time of the night, the 2-8am period so that's why the threat there will likely be lower. Still could change though and it all depends on how quickly this storm ramps up and where.
 
Rain Cold said:
It's hard for me to buy the NAM's long range stability predictions. I have seen them bust high so many times. That said, the dynamic nature of the system and the wind energy upstairs raises the concern level. We'll have to see how things are looking from a completely overcast vs. broken sky standpoint as we near Friday. That will likely be the difference between spotty to numerous severe weather reports and a widespread outbreak.
Click to expand...

Yeah it seems a bit high to me but I noticed that the GFS and other globals are showing high temps Friday in the upper 70s to near 80, the main difference being the GFS and some other models have dewpoints in the 63-66 range whereas the NAM is 67-72. That can make a big difference this time of year when temps are in the 70s. We'd better hope the NAM is wrong with the instability it's showing or else it is going to be a VERY active day Friday across our area. Even the weaker instability of the GFS and other models would pose issues due to the strong LLJ and 925mb winds of 50-60kts across Central and Eastern NC.
 
Downeastnc said:
SPC write up had a interesting tid bit....

...Synopsis and Discussion...
Deep upper trough extending along the MS Valley early Friday morning
is expected to continue eastward, maturing into a well-formed
mid-latitude cyclone centered over the southern Appalachians by the
end of the period. Very strong flow aloft will exist throughout the
base of the upper trough, with the strongest flow developing within
its eastern periphery Friday afternoon and continuing into Saturday
morning. 500-mb flow could exceed 100 kt, which is near record
values across the Carolinas and into the mid-Atlantic based on SPC
sounding climatology. In contrast to these impressive dynamics,
overall thermodynamic environment will be marginal. Given that ample
low-level moisture will be in place (i.e. dewpoints in the mid 60s
to low 70s and 100-mb mean mixing ratios over 12 g/kg), the modest
instability is largely a result of warm temperatures aloft and
consequent poor lapse rates.
Click to expand...

And they are banking on weak instability. If the instability turns out to be higher than they are thinking that will just add more fuel to the fire here.
 
snowlover91 said:
And they are banking on weak instability. If the instability turns out to be higher than they are thinking that will just add more fuel to the fire here.
Click to expand...

Any SE surface winds combined with what the NAM shows ( 2000-3000 jkg ) is dangerous, tornado threat hinges on whether SFC winds can manage to back from the SE
 
snowlover91 said:
Latest 3km NAM has a broken line segment and multiple individual cells across parts of GA and the Carolinas.
View attachment 19117
Click to expand...

Soundings supports tornadoes all over central NC with sfc winds coming out of the SE, there is VBV in this sounding but I’m honestly ignoring it, this sounding anyways supports damaging winds with dry air aloft between 850 hPa and 500 hPa and decent PWAT which would allow for water loading, and plus that LLVL jet, this sounding anyways supports more low topped convection
B7A529E1-1E28-42BF-A0A1-CF11EC16A498.png
 
Myfrotho704_ said:
Soundings supports tornadoes all over central NC with sfc winds coming out of the SE, there is VBV in this sounding but I’m honestly ignoring it, this sounding anyways supports damaging winds with dry air aloft between 850 hPa and 500 hPa and decent PWAT which would allow for water loading, and plus that LLVL jet, this sounding anyways supports more low topped convection
View attachment 19118
Click to expand...

Yeah I think the main deal with this system is going to be damaging winds, especially if a line forms they could be pretty widespread with the LLJ forecast. Any cells that can develop ahead of the main line will be the ones to watch for a supercellular structure and possible tornadoes. A lot will depend on the position of our system and how quickly it cranks up, right now the LLJ really explodes just offshore. If it cranks up a bit faster than that would be even worse.
 
GFS sounding for Eastern NC in the band of enhanced 850mb winds. Not much instability but look at the winds... 60kts at only 1,000 feet above the ground. It sure won't take much to get that to the surface even in gusts with some of these storms.

1555517886874.png
 
Rain Cold said:
It's amazing the NAM and GFS are always so different with their CAPE depictions. NAM seems to always be so much higher. I guess it's just the same as it is in winter...crappy.
Click to expand...

Normally in between happens, GFS underdoes CAPE sometimes by a 1000 jkg while the nam will spit out to much (500-1000jkg more than verification)
 
Beginning to worry a little about south MS/AL tommorow STP is extreme. And simulated radar shows supercells ahead of the line. Screenshot_20190417-115717_Samsung Internet.jpgScreenshot_20190417-115702_Samsung Internet.jpg
 
May end up like a bust like last event but if it isn't the environment is very volatile tomorrow. No wonder spc has a significant hatched area for tornadoes tomorrow.
 
Myfrotho704_ said:
Normally in between happens, GFS underdoes CAPE sometimes by a 1000 jkg while the nam will spit out to much (500-1000jkg more than verification)
Click to expand...
Yeah, that's true. I'd probably lean closer to the GFS than the NAM. In this case, warmer air aloft and cloud cover should save us. The dynamics are going to be very good, and some decent wind should mix down. But I am still on the fence about a widespread, long-duration severe wind event. Heavy rain is almost certain, and I imagine even sub-severe winds will be able to more efficiently bring down trees, given the soil conditions.
 
You must log in or register to reply here.
Back
Top