Another wild night in Tornado Alley

By: Dr. Jeff Masters , 11:40 AM GMT on May 06, 2007

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The sirens sounded two more times in tornado-ravaged Greensburg, Kansas last night, as two more twisters tore through the county. However, both tornadoes missed populated areas, as did most of the approximately 75 tornadoes that touched down yesterday. The action should quiet down considerably today; the Storm Prediction Center (SPC) has placed most of Kansas and Nebraska under its "Slight Risk" area for severe weather. Sweetwater, Oklahoma received significant damage from a tornado last night, and we've saved 300 Kb animations of the radar reflectivity and Doppler velocities of the tornado.

It will take a long time for Greensburg to recover from Friday's tornado. To get an idea of the scale of devastation, see the aerial photos posted by the Wichita Eagle. Damage surveys are not yet complete on the tornado, but photos I've seen of the destruction show damage consistent with EF4 winds(168-199 mph). It is possible the storm was an EF5 (winds more than 200 mph). The nine deaths from the tornado bring the U.S. tornado death toll to 68 so far this year, two more than the toll for all of last year.

We've saved some extraordinary 1 Mb animations of the radar reflectivity and Doppler velocities of the tornado. I asked wunderground meteorologist and tornado expert Rob Carver to comment on what's going on in the animations, and here was his analysis:

This was likely an example of cyclic mesocyclogenesis. In a nutshell, the rear-flank downdraft surges out, wraps around and occludes the mesocyclone (Meso A for short). Meso A then veers to the left and dies, this is why tornado family members curve to the left as they dissipate. While Meso A is dying, a new meso spins up and becomes the dominant meso. Now, while I've seen plenty of simulated cyclic cases where the hook retreats when Meso A occludes, I don't think I've seen anything as dramatic.



Figure 1. Radar image of the storm that spawned the Greensburg, KS tornado of May 4, 2007, showing the clearly defined hook echo associated with the twister.

Coastal Carolina storm
The latest (8pm EDT) computer forecast models continue to show a moderately strong coastal storm developing several hundred miles southeast of Cape Hatteras, North Carolina, on Monday. The storm will be extratropical in nature when it forms. We'll have a lot of time to watch the storm, as it is expected to meander offshore for five days and gradually weaken. Water temperatures are 22-23 C off of the coast, which may be warm enough to allow the low to acquire some subtropical characteristics and become the season's first named storm. The models are hinting that the storm could remain over water long enough for this to happen, and I put the odds of a Subtropical Storm Andrea forming late this week at about 20%.

Wunderblogger Mike Theiss was out chasing yesterday and caught some of the storms; be sure to tune into his blog over the next few days to read his chase accounts. Stormchaser Dan Robinson posted some video stills of the Greensburg tornado.

Jeff Masters

()
Storm Brewing (thomasanthony)
A big storm moved in on the 3rd. Wasn't as bad as it looked though.
Storm Brewing

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384. GetReal
9:27 PM GMT on May 06, 2007
I do not believe that the NHC will name this system as a sub-tropical, or tropical storm, due to political and economic considerations. The NHC probably will not want to fan the media hype of an early and very active season starting this early. If it develops further...
Member Since: July 4, 2005 Posts: 204 Comments: 8806
383. melwerle
9:27 PM GMT on May 06, 2007
I'm in Savannah so wondering what time frame we're looking at. Guess I'll sit and wait.
Member Since: June 28, 2006 Posts: 12 Comments: 1837
382. southbeachdude
9:25 PM GMT on May 06, 2007
hello everyone.....this is a florida question...Will these storms make it all the way down to Miami or will they fizzle out before that? It seems like most days storms fizzle out around dusk. Thanks
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381. Drakoen
9:25 PM GMT on May 06, 2007
Posted By: melwerle at 9:24 PM GMT on May 06, 2007.

ok - so when is this storm supposed to start heading south? (if it does head south). What kind of time frame are we talking about or are we waiting to see what the nhc says at 5?


I dont think they give out 5 pm discussion during the off season. There is still some uncertainty about where this system will go. The most likely scenario is around N Florida, Georgia, South Carolina landfall. This could change.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
380. Drakoen
9:23 PM GMT on May 06, 2007
Posted By: weathersp at 9:23 PM GMT on May 06, 2007.

I can see on floter one that the shear is about 50kts over where the center is

the shear is expected to decrease quite dramitcally over that area as the system tries to develop. The winds in the Low are generally 36 mph gusting to tropical storm force.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
379. RL3AO
4:24 PM CDT on May 06, 2007
post removed
377. melwerle
9:22 PM GMT on May 06, 2007
ok - so when is this storm supposed to start heading south? (if it does head south). What kind of time frame are we talking about or are we waiting to see what the nhc says at 5?

Member Since: June 28, 2006 Posts: 12 Comments: 1837
376. weathersp
5:20 PM EDT on May 06, 2007
I can see on floter one that the shear is about 50kts over where the center is.
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375. HurricaneRoman
9:18 PM GMT on May 06, 2007
* SEVERE THUNDERSTORM WARNING FOR...
NORTHEASTERN BROWARD COUNTY IN SOUTH FLORIDA.
SOUTH CENTRAL PALM BEACH COUNTY IN SOUTH FLORIDA.

* UNTIL 600 PM EDT

* AT 513 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING BASEBALL SIZE
HAIL...AND DESTRUCTIVE WINDS IN EXCESS OF 70 MPH. THESE STORMS
WERE LOCATED ALONG A LINE EXTENDING FROM LOXAHATCHEE NATIONAL
WILDLIFE REFUGE TO 10 MILES SOUTHWEST OF WELLINGTON...OR ALONG A
LINE EXTENDING FROM 10 MILES WEST OF BOYNTON BEACH TO 18 MILES EAST
OF BELLE GLADE...AND MOVING SOUTH AT 30 MPH.


Whoa!!!! BASEBALL size hail!!! I dont think i have ever read that on a warning here in South florida
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374. hurricane23
17:22 EDT le 06 mai 2007
TORNADO WARNING!!!!

G
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373. Drakoen
9:21 PM GMT on May 06, 2007
Maybe the NHC will send out a special weather statement. There is currently a severe thunderstorm warning for my area as the cell moves closer to my location in Lake Worth.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
372. chessrascal
9:19 PM GMT on May 06, 2007
this is almost as fun as a hurricane lol
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369. Hellsniper223
9:18 PM GMT on May 06, 2007
Anyone have a link that could explain the time system they use on NHC updates and Model runs?
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368. StormJunkie
9:16 PM GMT on May 06, 2007
Afternoon all.

Winds have picked up here in Charleston due to the pressure gradient. Looks like shear is having fun with the low right now.
Member Since: August 17, 2005 Posts: 26 Comments: 15644
367. sarepa
9:18 PM GMT on May 06, 2007
nvm ignore wat i just said
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365. Drakoen
9:16 PM GMT on May 06, 2007
I will be really intersted in this system when it starts getting thunderstorms around its center. Currently the convective activity is just increasing on the out edge 100 miles out from the center. Where winds are sustained at tropical depression strength. I hope the NHC will have more on the system before its next discussion.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
363. Hellsniper223
9:15 PM GMT on May 06, 2007
Oh, my Bad.
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362. Drakoen
9:14 PM GMT on May 06, 2007
the storm cell is Plam Beach Count is heading in my direction its already raining here. There are so many things going on. The Low Pressure and the thunderstorms in Florida.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
361. Thundercloud01221991
9:12 PM GMT on May 06, 2007
Floater 1 is right on it not 4
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359. weathersp
5:04 PM EDT on May 06, 2007
Greensburg Tornado In HD radar.

Greensburg Tornado

To See full Image Click Here
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358. hurricane23
17:08 EDT le 06 mai 2007
Rotation with this tunderstorm heading for the lake.

Free Image Hosting at www.ImageShack.us
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357. Hellsniper223
9:10 PM GMT on May 06, 2007
Kinda looks like they're moving #4 into position.
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356. HurricaneFCast
9:09 PM GMT on May 06, 2007
No problem StormW.
Member Since: April 20, 2007 Posts: 7 Comments: 1482
355. Thundercloud01221991
9:07 PM GMT on May 06, 2007
Winds at bouy 41001 have increased again not to 35 knt sustained winds and 42.7 knt wind gusts
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352. sporteguy03
9:06 PM GMT on May 06, 2007
Jp,
It felt like a tornado was forming I live 15 miles from Haines City, dark gray-greenish skies.
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351. HurricaneFCast
9:06 PM GMT on May 06, 2007
StormW- Link
Member Since: April 20, 2007 Posts: 7 Comments: 1482
348. Drakoen
9:03 PM GMT on May 06, 2007
Posted By: HurricaneFCast at 9:02 PM GMT on May 06, 2007.

Drakoen- It will be very active. A La Niņa is forming..Expect light to moderate La Niņa conditions this summer, which will increase SST's in caribbean and the moisture content as well, it will also decrease Vertical Wind Shear ubiquitously across the Atlantic Basin, both which will aid in increased activity this Hurricane Season.

We are experiencing Typical La Nina condtions with dry southeast, which makes for a rather active season. I wouldn't mind a tropical depression coming through Palm Beach County where i live. The shear is starting to drop this early... and the SST's are ready to support tropical cyclogenesis
Member Since: October 28, 2006 Posts: 57 Comments: 29886
347. HurricaneFCast
9:05 PM GMT on May 06, 2007
The Greensburg Tornado was about a Mile wide. It was huge.
Member Since: April 20, 2007 Posts: 7 Comments: 1482
346. HurricaneFCast
9:02 PM GMT on May 06, 2007
QuikSCAT already shows 45kt sustained around 34N, 76W
Member Since: April 20, 2007 Posts: 7 Comments: 1482
345. chessrascal
9:03 PM GMT on May 06, 2007
that tornado was huge i didnt realize the size till that link was posted!
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344. hurricane23
17:04 EDT le 06 mai 2007
Severe thunderstorms with large hail very possible in many places across florida...

ggg
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342. Drakoen
9:02 PM GMT on May 06, 2007
Posted By: MichaelSTL at 8:44 PM GMT on May 06, 2007.

The CMC and NAM are still forecasting a tropical storm; in fact, it is already warm-core but frontal


one thing though should we trust the path at which those models are predicting the systems to take?
Member Since: October 28, 2006 Posts: 57 Comments: 29886
339. HurricaneFCast
9:00 PM GMT on May 06, 2007
Drakoen- It will be very active. A La Niņa is forming..Expect light to moderate La Niņa conditions this summer, which will increase SST's in caribbean and the moisture content as well, it will also decrease Vertical Wind Shear ubiquitously across the Atlantic Basin, both which will aid in increased activity this Hurricane Season.
Member Since: April 20, 2007 Posts: 7 Comments: 1482
337. chessrascal
8:58 PM GMT on May 06, 2007
radar

Storm Predators radar image.
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336. hurricane23
17:00 EDT le 06 mai 2007
Yea stormw TS winds blowing threw bouy 41001
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335. Drakoen
8:58 PM GMT on May 06, 2007
The fact that tropical cyclogenesis is a probability this early is making me question the rest of this season to be very active.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
334. sporteguy03
8:57 PM GMT on May 06, 2007
JP,
6000 Lightning Strikes in Central FL since 12 noon!
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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