Tornado Watch

[HAltschule]

What evidence do you have that it's a supercell?

There is (or was) a clearly defined S-R Velocity couplet at 0.5 degrees. Clearly symmetrical rotation aloft in 1 cell only. That sustained rotating cell obviously is a supercell.

 

[HAltschule]

I should clarify.... There is a line or feeder band, yes. But there are normally numerous individual cells within that line. Thats what we're looking at.

 

[nickgrillo]

It looks more like a Squall line than a supercell. It's got a defined area of rotation about, 1.2 nm. What evidence do you have that it's a supercell? Scott, are you saying that their NEVER is enough instability since your near water?

Often there isn't much instability associated with hurricane-spawned supercells... Now, in this case - instability is somewhat decent, with at least >1000J/KG of CAPEs well inland in most locations. That storm was showing some defined supercell characteristics for a few scans... Now it's all embedded with the rest of the convection. While the TOR has expired, any of these storms could quickly produce a tornado as they move inland.

 

[Scott Olson]

It looks more like a Squall line than a supercell. It's got a defined area of rotation about, 1.2 nm. What evidence do you have that it's a supercell? Scott, are you saying that their NEVER is enough instability since your near water?

No being near water has nothing to do with it, it's a delicate balance between instability and shear. These tropical disturbances have an abudance of shear avaliable the key is when some instability *buoyancy* can develop, even just a little in the right shear environment can do the trick.

 

[Andrew Khan]

Ahh, I just looked, and I saw the rotation...thanks.

 

[rdale]

.deleted.

 

[Jeff Snyder]

Posting rules in this special, one-time-only forum are relaxed from what is be expected in the rest of Stormtrack. That said, it is certainly appreciated that we all try to keep frivolous posts to an absolute minimum. Please refrain from making frivolous or otherwise not benecial posts.

 

[Scott Olson]

KLIX:
CAPE (B+): 872.16 J/kg
Storm rel helicity (0-3000m) pos: 393.0 neg: -13.3 tot: 379.7 m^2/s^2
Bulk Shear: 70.50 m/s

Not to bad instability with all the squalls and cloud cover around.

 

[Dave Kaplow]

Look at all the mini-sups lined up in the NE quadrant right now! Almost all of them are showing some signs of rotation. Here’s a saved radar image:

If Katrina continues to be this prolific in producing semi-isolated convection in the outer rainbands, there could be a lot of damage well before the storm even makes landfall. She's currently in the middle of an ERC, but that shouldn't effect the outer bands at all.

I bet there's more than one tornado under those cells, the potential is definitely there.


Edit: Oops, I didn't see the "Tornado Warning" thread in time, or I might have posted this there. Mods feel free to move my post if you think it belongs in the other thread.

 

[Jeff Snyder]

It's interesting that the SPC has indicated a MDT risk across parts of se US in association with Katrina. It's rather rare for the SPC to do MDT risk / 15% tornado prob with a landfalling hurricane. MDTs aren't as rare a day or two after after landfall as the cyclone fills, but I dont' thik I've ever seen a MDT risk the day of a landfall. Low-level shear is extreme, and insolation should load to significant instability by afternoon.

 

[SteveCarter]

Many canes are tornado-producers, ie Ivan and Frances last year. Ivan produced 117 tornadoes, and even Frances produced 101, with 45 tornadoes in South Carolina alone, where I live. Most of these, if not ALL of them, were produced suddenly, with very little warning, and were not a by-product of a well-defined supercell. These are so hard to forecast because nearly every storm in a hurricane band has SOME type of rotation, given the fact that winds are usually in excess of 60kts, and wind shear is so intense. These F-0's - F-2's can still cause a great deal of damage and fatalities as well. Ivan killed 8 by tornadoes, and Jeane killed a woman in Fairfield County, Sc, and Frances killed as well. We are bracing for a possible tornado "outbreak" here later tonight, and even the official weather forecast is saying "isolated tornadoes" possible. Even though most of these tubes are short-lived, and weaker than most, they still can kill, and cause a GREAT deal of damage.

 

[Scott Olson]

Many canes are tornado-producers, ie Ivan and Frances last year. Ivan produced 117 tornadoes, and even Frances produced 101, with 45 tornadoes in South Carolina alone, where I live. Most of these, if not ALL of them, were produced suddenly, with very little warning, and were not a by-product of a well-defined supercell. These are so hard to forecast because nearly every storm in a hurricane band has SOME type of rotation, given the fact that winds are usually in excess of 60kts, and wind shear is so intense. These F-0's - F-2's can still cause a great deal of damage and fatalities as well. Ivan killed 8 by tornadoes, and Jeane killed a woman in Fairfield County, Sc, and Frances killed as well. We are bracing for a possible tornado "outbreak" here later tonight, and even the official weather forecast is saying "isolated tornadoes" possible. Even though most of these tubes are short-lived, and weaker than most, they still can kill, and cause a GREAT deal of damage.

Most of those tornadoes we were not during the Hurricane stage but instead during the T.S. or T.D. stage. Both of those systems were profilic tornado producers once there cloud cover dwindled a bit and shear was a little less extreme in vicinity.

 

[Dave Kaplow]

I remember reading that big tropical cyclone tornado outbreaks are usually associated with dry air intrusions into the storms' circulations. If that theory is true, you would tend to see a kind of inverse relationship between the strength of a storm and its capacity to produce a lot of tornadoes. Sure enough, historically I believe most major outbreaks have occurred with weak or weakened storms. I imagine it's quite rare to see a major hurricane produce a major outbreak of tornadoes immediately on or before the storm itself makes landfall.

Of course, any tornado occurring directly in the path of cat-3 or higher winds is going to be both impossible to confirm and unlikely to be reported. This bias might partially explain why major hurricanes are seldom associated with big tornado outbreaks, although you would think that this would be taken into consideration by anyone doing serious research in the area. In any event, Katrina could be spawning tubes by the dozen right now and we'd have no real way of knowing about it. Reports will trickle in, and eventually the entire picture will emerge, but not any time soon.

The Mod risk seems like a perfectly reasonable action given the current lack of data, and the many rotating cells we saw in the outer bands yesterday.

 

[nickgrillo]

Yeah... The MDT risk for today seems perfectly reasonable. Low-level shear is absolutely extreme with SRH >800 in a large portion of AL/MS, with SFC-based instability slowly increasing.

* AT 1153 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR THE EYE OF
DANGEROUS HURRICANE KATRINA MOVING NORTH THROUGH PEARL RIVER
COUNTY...MOVING NORTH AT 16 MPH. THE INTENSE EYEWALL WINDS AROUND
THE CENTER OF KATRINA ARE AFFECTING AREAS FROM NORTHERN WASHINGTON
PARISH LOUISIANA ACROSS NORTHERN PEARL RIVER COUNTY MISSISSIPPI.

There's another one of the eye-wall based TORs. Like someone said before, I'm not sure there would be too much use for them... :lol: :lol:

 

[HAltschule]

Amazing. Max 0-3 SRH is 1200+ right now. Looks like we have to keep a close eye on AL (especially Central and Eastern) where signifcant heating with Capes 1500+ are occurring. I wouldn't be surprised if we see some strong tornadoes develop there between now and 7pm. Everything parameter looks favorbale for TOR's.

EDIT: I mean to say AL is what we have to watch.