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Posted on 3/1/12 at 3:49 pm to Luke
It came closer than even the path shows. That day haunts everyone in Tuscaloosa. I hope to never relive that again, but days like tomorrow make it impossible to forget.
Posted on 3/1/12 at 3:50 pm to ACL11190
I can remember as a kid being up in a magnolia tree in my parents front yard, hearing the siren go off and looking out (we're on top of a hill) and being able to see the tornado. Amazing I did not break something how quickly I got down out of that tree. Only time I've ever seen a tornado like that, in Alabama there are so many trees and hills and the storms are often veiled in rain, they sneak up on you. Hate seeing it turn green outside when these things come in.
Posted on 3/1/12 at 3:51 pm to Doldil
quote:
Doldil
Don't feel bad, it's my fault. I'm hoping it's only these two teeth and no more decided to die on me
All of the states in Dixie Alley and Tornado Alley need a break from this weather.
Posted on 3/1/12 at 3:53 pm to Ball Gravy
quote:This is not always correct.
Dry Lines and Frontal Boundaries (squall lines) vs. Warm Sectored Atmosphere and Daytime Heating (discrete cells)
While yes, QLCS(squall lines) are on or along boundaries, you can have a line of supercells along said boundary given enough shear. See the NC outbreak that was a QLCS that was broken up into individual cells as an example.
Edit: grammar
This post was edited on 3/1/12 at 3:59 pm
Posted on 3/1/12 at 3:55 pm to ACT
You're right but he was asking how discrete cells form and why.
You can find supercells embedded in squall lines or just a touch in front, but these are always a) defined as part of the squall line and b) typically much weaker than your discrete cells due to the convective heating.
You can find supercells embedded in squall lines or just a touch in front, but these are always a) defined as part of the squall line and b) typically much weaker than your discrete cells due to the convective heating.
Posted on 3/1/12 at 4:01 pm to Ball Gravy
quote:If embedded in a line, aren't they usually weaker due to inflow obstruction as opposed to heating? I've seen some nasty EF-4's at 3am.
weaker than your discrete cells due to the convective heating
Posted on 3/1/12 at 4:08 pm to ACT
Yes.
Tornadic storms like to begin in relatively uncapped air with at least sufficient CAPE to get an updraft to survive without being blown too far over by the deep layer vertical wind shear. The lack of CIN allows air parcels to rise from the near the ground into a convective updraft with relative ease producing what we call surface-based convection.
You get surface based convection in these heating storms, whereas you get these deep layers as a boundary or fronts approach and these tornadic cells in the squall line tend to be short lived and weaker.
Tornadic storms like to begin in relatively uncapped air with at least sufficient CAPE to get an updraft to survive without being blown too far over by the deep layer vertical wind shear. The lack of CIN allows air parcels to rise from the near the ground into a convective updraft with relative ease producing what we call surface-based convection.
You get surface based convection in these heating storms, whereas you get these deep layers as a boundary or fronts approach and these tornadic cells in the squall line tend to be short lived and weaker.
Posted on 3/1/12 at 4:12 pm to Ball Gravy
Another thing... squall lines tend to be positively tilted storms whereas discrete tend to be negatively titled storms.
Negatively tilted storms allow more updraft that is perpendicular to the surface (creating shear) whereas positively tilted storms have a parallel wind field (straight line winds)
FYI... here are their meteorological society explanations.
NEGATIVE TILTED TROUGH- A trough which tilts from the northwest toward the southeast. This situation creates instability since cold temperatures in the mid and upper levels advect over warmer air at the surface. A negative tilt is a sign a trough is mature.
POSITIVE TILTED TROUGH- A trough which tilts from the northeast toward the southwest. Often a trough is positive tilted in it's development stage.
From: National Weather Service:
Negative-Tilt Trough: An upper level system which is tilted to the west with increasing latitude (i.e., with an axis from southeast to northwest). A negative-tilt trough often is a sign of a developing or intensifying system.
Positive-Tilt Trough: An upper level system which is tilted to the east with increasing latitude (i.e., from southwest to northeast). A positive-tilt trough often is a sign of a weakening weather system, and generally is less likely to result in severe weather than a negative-tilt trough if all other factors are equal.
Negatively tilted storms allow more updraft that is perpendicular to the surface (creating shear) whereas positively tilted storms have a parallel wind field (straight line winds)
FYI... here are their meteorological society explanations.
NEGATIVE TILTED TROUGH- A trough which tilts from the northwest toward the southeast. This situation creates instability since cold temperatures in the mid and upper levels advect over warmer air at the surface. A negative tilt is a sign a trough is mature.
POSITIVE TILTED TROUGH- A trough which tilts from the northeast toward the southwest. Often a trough is positive tilted in it's development stage.
From: National Weather Service:
Negative-Tilt Trough: An upper level system which is tilted to the west with increasing latitude (i.e., with an axis from southeast to northwest). A negative-tilt trough often is a sign of a developing or intensifying system.
Positive-Tilt Trough: An upper level system which is tilted to the east with increasing latitude (i.e., from southwest to northeast). A positive-tilt trough often is a sign of a weakening weather system, and generally is less likely to result in severe weather than a negative-tilt trough if all other factors are equal.
This post was edited on 3/1/12 at 4:19 pm
Posted on 3/1/12 at 4:22 pm to Ball Gravy
quote:
You're right but he was asking how discrete cells form and why.
You can find supercells embedded in squall lines or just a touch in front, but these are always a) defined as part of the squall line and b) typically much weaker than your discrete cells due to the convective heating.
I didn't word my question to you well but you answered it well. ACT actually hit on what I was trying to get at as well. I understand the instances where a supercell forms just ahead of the main squall line. I'm wondering more about what ingredients create a large number of discrete super cells well ahead of any QLCS that eventually forms and sweeps through an area. On April 27th the convective mode was almost exclusively super cells that were forming everywhere at an alarming rate. It wasn't until the tail end of the event that what I would consider a meager QLCS formed (at least in the Alabama portion of the storm) and this passed with little fanfare. Not only was the number of tornadic super cells incredibly rare but the duration at which they continued and the odd lack of a typical squall line to sweep everything out.
EDIT: I could be totally wrong but I don't think the trough on April 27th went negative tilt. Again, I could be totally wrong about that and wouldn't be suprised if I was given it usually takes a trough going negative tilt to produce like April 27th did.
This post was edited on 3/1/12 at 4:26 pm
Posted on 3/1/12 at 4:51 pm to RollTide1987
quote:
Major tornado outbreak expected tomorrow
Posted on 3/1/12 at 5:08 pm to tigerfan in bamaland
High Impact Severe Weather Event Friday
We are bracing for another HIGH IMPACT severe weather event tomorrow evening. This includes a threat for strong tornadoes including those that create EF3 and above damage. The atmosphere will get primed today with a warm front lifting to the north during the afternoon. In fact, a few strong storms are not out of the question later today as we become more and more unstable. Temperatures will climb into the mid to 70s this afternoon with a strong southerly wind. We'll be even warmer tomorrow with highs reaching 80. Models suggest two low pressure areas forming - the one just to our north will increase wind shear with low level winds reaching over 60kts during the afternoon and evening.
TIMEFRAME: We could see supercell thunderstorms developing ahead of the front as early as 6-7pm. It appears the main threat will come after 10pm and last through much of the overnight into early Saturday morning. I don't anticipate the threat to be over until 6am Saturday.
MAIN CONCERNS: Long-track strong tornadoes and damaging straight-line winds. We could see all modes of severe weather with this event. I anticipate isolated cells to develop in the "warm sector" of this system ahead of the cool front. We will also see spin-ups embedded within the squall line during the overnight hours. While one of many indexes we use to forecast severe weather - the Significant Tornado Parameter is painting a major tornado threat across Alabama with values between 4-6. Values over three indicate a good potential for stronger and more violent tornadoes.
WHERE: It appears the threat will be widespread across the entire area. Models are suggesting the threat will be highest north of I-20. In Alabama - my greatest concern would be cities in and around Tuscaloosa, Jasper, Cullman, Birmingham, Hamilton, Florence, and Huntsville. In fact, I believe we will experience severe weather throughout Tennessee and Kentucky as well. This threat should not include areas south of Montgomery. The Storm Prediction Center shows the highest probability for severe weather (the 45% hatched) area in North Central Alabama.
CALL TO ACTION: This is the time you need to start thinking about your severe weather plan and have it in place. Make sure you have a method to get warnings - weather radio, mobile phone app, etc. I encourage multiple levels of warnings. If you have friends or neighbors that typically do not stay weather aware - make a point to call them today and give them a heads up about the threat. In addition - remember helmets for the kids.
Posted on 3/1/12 at 5:11 pm to tigerfan in bamaland
I was at home watching the computer the morning of the T-town out break. I have never seen the number of super cells forming with out a defined line. They were crossing the state line from mid morning until 8pm. When the one which hit Tuscloosa came across the state line the cell was 53,000feet. It was bad and got worse.
Posted on 3/1/12 at 6:07 pm to geauxranger54
I'm guessing based on all of that, that Starkville will also be right in the middle of the Tornado threat tomorrow evening.
Posted on 3/1/12 at 6:18 pm to Herman Frisco
quote:
When the one which hit Tuscloosa came across the state line the cell was 53,000feet.
It's amazing how tall those supercells can get.
Posted on 3/1/12 at 6:25 pm to deltaland
I've not been on here since getting serially raped during the NCAA tourney last spring. From what I can determine, though, it looks like Cincy, Lexington, Louisville and Nashville are in the crosshairs tomorrow. We don't typically get those F-4 and 5 monsters around here, but it looks like it could happen tomorrow. Everyone stay safe.
Posted on 3/1/12 at 6:29 pm to Govt Tide
quote:This has to do with the amount of instability, shear, and lift available. A multitude of these minus a CAP on the atmosphere will allow air parcels to rise uninhibited to create supercells. The cold front itself creates it's own lift, so any remaining instability is used to create the QLCS. A CAP is just that, a cap of warm air above the surfaces that inhibits air from rising freely through the atmosphere.
I'm wondering more about what ingredients create a large number of discrete super cells well ahead of any QLCS that eventually forms and sweeps through an area.
quote:While this is true, remember that there were 2 rounds of storms prior to the explosive supercell development. The first, that morning, was an MCS (Mesoscale Convective System). It was basically a small low pressure that formed on an existing QLCS that moved through creating it's own lift and shear. Hence the alarming number of tornadoes that morning. Remember, Cordova, AL has the distinction of being the town that was hit twice that day. An EF-3 with the morning line, an EF-4 with a supercell that evening. When that first line moved through, a second line formed and went through the Tennessee Valley area around 10ish. Then, the ingredients were such that instead of being used up and reloading slowly, it was like an entire new and untouched area of instability just took it's place. The shear from the upper low then was so high that supercells formed and were not allowed to ever line up to to the shear keeping them separate. That's why the storms that day were moving at 60+mph. The meager line at the very end was the front itself, allowing our fears of more storms to subside. The atmosphere was just spent at that point..as it had been worked over multiple times.
On April 27th the convective mode was almost exclusively super cells
The number of supercells that day wasn't extremely rare, but the amount that were producing violent tornadoes was. You can watch videos of those tornadoes and see how violent the atmosphere was that day. Not only were they multiple vortex tornadoes, but in some, you can clearly see horizontal vortexes flowing into them as well.
Posted on 3/1/12 at 6:39 pm to ACT
Wow.....for those in that area, stay safe. I have a lot of friends in that zone.
Posted on 3/1/12 at 7:51 pm to RollTide1987
quote:
as well as the F4 that struck Piedmont, Alabama on Palm Sunday 1994.
yep. so sad killed those people in church. Coming from south louisiana, I was totally unaware of the active outbreak of large tornados in central and northern alabama.
Posted on 3/1/12 at 8:26 pm to sheek
LINK
quote:
The setup and aftermath on Friday for the Ohio and Tennessee valleys could be similar to the weather pattern during and following the 1974 Super Outbreak.
Spanning April 3-4, 1974, a swarm of tornadoes tore through areas from Illinois and southern Michigan to northern Alabama and Georgia.
The outbreak produced 148 confirmed tornadoes, six of which were F-5 intensity. The most powerful of these storms slammed into Xenia, Ohio.
Every weather pattern no matter how similar always has its differences, and this outbreak will have its own characteristics.
However, according to Severe Weather Expert Henry Margusity, "In the case of the end of this week and back in early April of 1974, it appears strong upper-level winds and cool air approaching from the west could hit a zone of advancing warm, moist air in just the right manner to produce monsters of thunderstorms."
This post was edited on 3/1/12 at 8:28 pm
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