Timhsv
Member
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Severe WX April 11th-13th, 2020 Severe Weather Threat
- Thread starter Taylor Campbell
- Start date
Austin Dawg
Member
Good night. Gotta get up and see what problems we will have here in central Texas tomorrow. Could not get an update so I'm waking up early.
brianc33710
Member
I thought that they would extend the MOD risk east & north. That didn't happen. But The upgrade on day 2 not pulling the High Risk trigger doesn't surprise me. Maybe the models are now less bullish for Sunday?
Equus
Member
I figured they might at least push it to the Georgia line, but might have to wait for D1 for any significant changes, not sure they'll change too much til then. Certainly wouldn't mind any downtrending between now and then haha
jmills
Member
(Disclaimer: My little rambling is focused on the east MS/AL area).
Currently the closed low in question is still out over the Baja region of California, however it is slowly starting to become progressive and move eastward, which it will continue to do over the weekend leading up to Sunday. Out ahead of this, high pressure over the Southeast is starting to shift to the east. This is setting up return flow off of the Gulf of Mexico into south Texas as I write this. Mid/upper 60 dews are already making their way inland across the southern boot of Texas.
The Gulf has had anomalously high sea surface temperatures for at least the past few weeks and this has helped to modify the air above it to form a very moist and warm source region for the warm sector that will form across the SE over the weekend.
Synoptically speaking, a very powerful jet streak embedded in the STJ is projected to overspread the region on Sunday. A common failure mode of these types of severe weather set ups in Dixie is a large mass of precipitation that forms over the Gulf Coast and inhibits the advection of unstable air northwards and can mess up the wind profiles. The placement of the jet max puts the right exit region right over the coast which will help to prevent that from happening. This also sets up a transverse circulation that will help to aid advection of Gulf air inwards. The large area of diffluence spreading over the region will contribute to large scale vertical ascent which will help to prime the atmosphere below and improve the thermodynamic situation.
At the surface a deepening surface low is sliding to the NE with pressure falls occurring all across the warm sector. The surface low placement around St. Louis is CLASSIC for big Dixie events.
Essentially every model has mid-ish 70 degree temperatures and upper 60s dewpoints into northern MS and central AL (pushing into the TN valley). To be honest, I think surface temperatures are probably under done by a few degrees given just how strong the advection is, and especially if we are able to get cloud breaks during the day. Any storms that form will likely explode in a very volatile environment, ala this 0z NAM sounding from the west AL:
This is a classic sounding. You have a large amount of instability (1800+ j/kg) with an LI of -6, indicative of a "fat" CAPE profile that will promote rapid parcel acceleration and stretching of any rotating updrafts. LCL's (a potential discriminator between tornadic and non-tornadic supercells) is squarely in the climatalogical range for large, violent tornadoes.
The kinematic profile is also very indicative of strong tornadoes. 1 km and 3km helicity values of 450 and 600+ respectively are both very significant and will contribute to rotating updrafts. The hard veering in the lowest 2 ish km on the hodograph (although not quite your classic "sickle") is indicative of a high amount of streamwise vorticity ingestion.
The sounding above shows a weak EML (capping layer) that will help to hold off excessive junk convection in the open warm sector, potentially leading to relatively unabated destabalization as the day goes on and allowing convection to be focused on more organized convergence zones. It also will contribute to heightened mid level lapse rates as the region undergoes large scale ascent.
A couple of questions arise though:
1.) If there is convection/precipitation in the warm sector, how organized will it be and can it grown upscale enough to stabilize sections of the warm sector?
The more interesting question is:
2.) If this early convection isn't enough to stabilize, will it only serve to focus convection and provide locally enhanced wind shear for the storms that do form?
Given just how potent this LLJ is and the quality of the gulf moisture being pulled up, I'm afraid #2 is a distinct possibility. This is a detail that will be worked out today (Saturday) and during the morning on Sunday.
Overall it looks like a significant tornado outbreak is possible Sunday afternoon/evening/night over a broad area. Stay informed and stay safe.
Currently the closed low in question is still out over the Baja region of California, however it is slowly starting to become progressive and move eastward, which it will continue to do over the weekend leading up to Sunday. Out ahead of this, high pressure over the Southeast is starting to shift to the east. This is setting up return flow off of the Gulf of Mexico into south Texas as I write this. Mid/upper 60 dews are already making their way inland across the southern boot of Texas.
The Gulf has had anomalously high sea surface temperatures for at least the past few weeks and this has helped to modify the air above it to form a very moist and warm source region for the warm sector that will form across the SE over the weekend.
Synoptically speaking, a very powerful jet streak embedded in the STJ is projected to overspread the region on Sunday. A common failure mode of these types of severe weather set ups in Dixie is a large mass of precipitation that forms over the Gulf Coast and inhibits the advection of unstable air northwards and can mess up the wind profiles. The placement of the jet max puts the right exit region right over the coast which will help to prevent that from happening. This also sets up a transverse circulation that will help to aid advection of Gulf air inwards. The large area of diffluence spreading over the region will contribute to large scale vertical ascent which will help to prime the atmosphere below and improve the thermodynamic situation.
At the surface a deepening surface low is sliding to the NE with pressure falls occurring all across the warm sector. The surface low placement around St. Louis is CLASSIC for big Dixie events.
Essentially every model has mid-ish 70 degree temperatures and upper 60s dewpoints into northern MS and central AL (pushing into the TN valley). To be honest, I think surface temperatures are probably under done by a few degrees given just how strong the advection is, and especially if we are able to get cloud breaks during the day. Any storms that form will likely explode in a very volatile environment, ala this 0z NAM sounding from the west AL:
This is a classic sounding. You have a large amount of instability (1800+ j/kg) with an LI of -6, indicative of a "fat" CAPE profile that will promote rapid parcel acceleration and stretching of any rotating updrafts. LCL's (a potential discriminator between tornadic and non-tornadic supercells) is squarely in the climatalogical range for large, violent tornadoes.
The kinematic profile is also very indicative of strong tornadoes. 1 km and 3km helicity values of 450 and 600+ respectively are both very significant and will contribute to rotating updrafts. The hard veering in the lowest 2 ish km on the hodograph (although not quite your classic "sickle") is indicative of a high amount of streamwise vorticity ingestion.
The sounding above shows a weak EML (capping layer) that will help to hold off excessive junk convection in the open warm sector, potentially leading to relatively unabated destabalization as the day goes on and allowing convection to be focused on more organized convergence zones. It also will contribute to heightened mid level lapse rates as the region undergoes large scale ascent.
A couple of questions arise though:
1.) If there is convection/precipitation in the warm sector, how organized will it be and can it grown upscale enough to stabilize sections of the warm sector?
The more interesting question is:
2.) If this early convection isn't enough to stabilize, will it only serve to focus convection and provide locally enhanced wind shear for the storms that do form?
Given just how potent this LLJ is and the quality of the gulf moisture being pulled up, I'm afraid #2 is a distinct possibility. This is a detail that will be worked out today (Saturday) and during the morning on Sunday.
Overall it looks like a significant tornado outbreak is possible Sunday afternoon/evening/night over a broad area. Stay informed and stay safe.
tornadoapril98
Member
I'm watching TWC, and Reynolds Wolf is hinting at a possible repeat of 4/27/11.
he is the same guy that said the blizzard in 93 was going to be mostly rain, since then , I have never been impressed lol I replaced him in Anniston at cbs40 way back in 1995
tornadoapril98
Member
Before or after hurricane Opal?
I was there at 40 during Opal...my first tv job. I was paid $20 a newscast! LOL
sak
Member
I have a problem with how James Spann keeps saying this won't be like April 27th because "events like that happen once every 40 years". This is a dangerous mentality.
Take a look at STPs:
Sends a shiver up my spine because of how eerily similar that looks compared to April 27, 2011. Again, I don't know that this event will even come close to measuring up to historic outbreaks of the past... but using the time between events is not science. This is another version of the gambler's fallacy (Yes, 00 should only come up on the roulette once every 38 spins, but it can definitely happen 5 spins apart or you could go 100 spins without it happening. That's statistical variance, and something that James Spann is not only not an expert on, but appears to be clueless on. The scientific parameters show a similar mix of ingredients over a similar part of the world compared to April 27, 2011. A perfect analog? No. But at some point you have to look at the data and say "This looks similar to 4/27/11 for a good chunk of MS/AL"
Take a look at STPs:
Sends a shiver up my spine because of how eerily similar that looks compared to April 27, 2011. Again, I don't know that this event will even come close to measuring up to historic outbreaks of the past... but using the time between events is not science. This is another version of the gambler's fallacy (Yes, 00 should only come up on the roulette once every 38 spins, but it can definitely happen 5 spins apart or you could go 100 spins without it happening. That's statistical variance, and something that James Spann is not only not an expert on, but appears to be clueless on. The scientific parameters show a similar mix of ingredients over a similar part of the world compared to April 27, 2011. A perfect analog? No. But at some point you have to look at the data and say "This looks similar to 4/27/11 for a good chunk of MS/AL"
PLEASE tell me what model is this... Is it a proprietary model? Just not seeing this kind of data anywhere.
Kory
Member
That's the 3km NAM.
So when I look at the 3k nam, I see this, bad enough, but still not that:
Kory
Member
These thermal boundaries will provide focus of convective initiation in a highly unstable warm sector. BMX references the shortwave breaking the cap as it kicks out, but this will provide extra focus points.
Kory
Member
At this point, the NAM is an outlier of CAMs with the northerly extent of destabilization.
skelly
Member
James Spann sounded the alarm appropriately on 4/27/11 and each event since then. Reading his latest blog entry he gives plenty of alert to be concerned and prepared for tomorrow. If he was the only info I could get on the weather I’d be ok with that.
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Personally, I wish we'd drop 4/27/11 comparisons because they do little good, but I suppose I understand why we do it.
Kory
Member
Large EML plume moving in tomorrow morning on the HRRR.
sak
Member
I don't disagree with the overall message, or that he isn't sounding the alarm. But he is specifically saying that it won't be like April 27th because those things happen "once every 40 years" and what I'm saying is that is wrong and a dangerous way of thinking.
Kory
Member
Yeah, I'm not big on it, but as humans, we like to have past experiences to give an idea of what to expect. Prior to 4/27, we didn't know what the ceiling was to an event. Now, we have one and it's easy to throw out in discussions.