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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134. pottery
1:00 PM AST on May 06, 2007
All wind, over water, produce waves.
Large waves are certainly caused by wind duration, as well, obviously. But prevailing current has an effect too. Opposing current will cause waves to " back-up " and become steeper and more dangerous. Also, once a wave has become larger than the ones around it, it catches more wind, and becomes faster moving. It then overtakes other large waves and adds them to its mass. Eventually the wave cannot sustain its own height ( its water, after all ) and it falls over ( breaks )
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133. Skyepony (Mod)
5:02 PM GMT on May 06, 2007
Satalite floater on RGB
Member Since: August 10, 2005 Posts: 162 Comments: 37461
132. Skyepony (Mod)
5:00 PM GMT on May 06, 2007
Here's a great link for comparing the shear forcast between the GFS, Nogaps & cnc. Not much agreement here either..
Member Since: August 10, 2005 Posts: 162 Comments: 37461
131. 147257
4:55 PM GMT on May 06, 2007
cyclonebuster i thought that you knew that by now in several post jeff masters says if a storm is stalling or really slow but blowing hard the waves will get bigger and bigger
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129. pottery
12:49 PM AST on May 06, 2007
Well, There is certainly no debris on the streets of Greenburg............
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128. pottery
12:47 PM AST on May 06, 2007
OK Ryang. We'll talk.......
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127. pottery
12:45 PM AST on May 06, 2007
That's true, CB.
Would not want to be boating out there this week.......
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126. hurricaneman23
4:42 PM GMT on May 06, 2007
any chance of any development in the next couple weeks?
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125. RL3AO
11:37 AM CDT on May 06, 2007
dnalia, the difference between EF5 and EF4 is that the EF5 tornado usually sweeps away the debris.
122. dnalia
4:26 PM GMT on May 06, 2007
Please excuse my stupid question, but how exactly do they determine the difference between an F4 and an F5 from the damage? Is there really that much discernable difference between damage caused by winds of 199 mph (upper end of f4) and that caused by 200 mph?
121. pottery
12:21 PM AST on May 06, 2007
Ryang, replied.

The Florida surfer-dudes and dudettes must be waxing up all now so...............
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120. Skyepony (Mod)
4:20 PM GMT on May 06, 2007
Forecasted wave hieghts & that's in Meters...

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119. pottery
12:13 PM AST on May 06, 2007
Those are pretty incredible photos of Greensburgh. Only 9 people were killed ? With destruction like that, one would expect more.
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118. seflagamma
11:14 AM EST on May 06, 2007
Good morning everyone,
Thanks for the update Dr Masters!

Wow, those folks just cannot catch a break; hope these storms leave them alone for a long time so they can rebuild their lives and their town.

Everyone have a beautiful Sunday.
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117. ryang
12:15 PM AST on May 06, 2007
Nice 23...it has a nice round shape...so it has to get a surface circulation!!
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116. ryang
12:14 PM AST on May 06, 2007
Morning all...

Pottery you have mail...
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115. hurricane23
12:14 PM EDT on May 06, 2007
12z GFS intensifys a bit but keeps offshore as it gradually weakens.

ddd
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114. lilmax
4:09 PM GMT on May 06, 2007
ANZ085-062030-
BALTIMORE CANYON TO HATTERAS CANYON OUT TO 36N 70W TO 34N 71W
1030 AM EDT SUN MAY 6 2007

...HURRICANE FORCE WIND WARNING...

...N WALL OF GULF STREAM NEAR 35N 75.3W...36.2N 74.4W...36.8N
72.6W...37.3N 72W...

.THIS AFTERNOON...N WINDS 30 TO 40 KT NW PORTION AND E TO SE 25
TO 35 KT SE PORTION...BECOMING N TO NE THROUGHOUT AND INCREASING
TO 40 TO 50 KT...EXCEPT 50 TO 65 KT NEAR THE GULF STREAM...AND
SHIFTING WINDS 25 TO 35 KT OVER FAR SE PORTION. SEAS 4 TO 8
FT... EXCEPT 8 TO 13 FT FAR W PORTION...BUILDING TO 12 TO 18
FT... EXCEPT TO 26 FT NEAR THE GULF STREAM...AND 6 TO 12 FT OVER
FAR SE PORTION. RAIN AND TSTMS.
.TONIGHT...WINDS BECOMING NE 35 TO 45 KT...EXCEPT 45 TO 60 KT
FROM THE GULF STREAM SE. SEAS BUILDING TO 14 TO 22 FT...EXCEPT
22 TO 32 FT FROM THE GULF STREAM SE. RAIN AND SCATTERED TSTMS.
.MON...E TO NE WINDS DIMINISHING TO 25 TO 35 KT...EXCEPT 35 TO
50 KT FROM THE GULF STREAM SE. SEAS 12 TO 20 FT...EXCEPT 20 TO
30 FT FROM THE GULF STREAM SE. SCATTERED SHOWERS AND TSTMS.
.MON NIGHT...E TO NE WINDS DIMINISHING TO 30 TO 40 KT...HIGHEST
NEAR THE GULF STREAM...EXCEPT 20 TO 30 KT N OF 36N. SEAS
SUBSIDING TO 11 TO 18 FT...EXCEPT TO 24 FT IN THE GULF STREAM.
SCATTERED SHOWERS AND TSTMS S.
.TUE...E TO NE WINDS DIMINISHING TO 15 TO 25 KT...EXCEPT 10 TO
15 KT OVER FAR NW PORTION. SEAS SUBSIDING TO 9 TO 14
FT...HIGHEST SW.
.WED...WINDS BECOMING E TO SE 10 TO 15 KT. SEAS SUBSIDING TO 6
TO 9 FT LATE...HIGHEST SW.
.THU...S TO SE WINDS 10 TO 15 KT. SEAS SUBSIDING TO 4 TO 6 FT.
$$

It's already having hurricane force winds!
113. scottsvb
4:07 PM GMT on May 06, 2007
look at the 12Z GFS for example..also look at 24hrs...500mb that shows ya the ridging and all.
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112. lilmax
4:07 PM GMT on May 06, 2007
It'd probably do a little loop like Jeanne 2004.
111. StormJunkie
4:02 PM GMT on May 06, 2007
Sorry scott, you have lost me there. Little bit more laymans terms? And if the high was not there, would this low not go north over the next couple of days?

Member Since: August 17, 2005 Posts: 26 Comments: 15872
110. scottsvb
4:04 PM GMT on May 06, 2007
There is No ridge to its North... The ridge is currently elongated from Lousiana to Ohio...its eastern edge is the cold front sagging backdoor thru GA and N florida and its western edge is over the plains.
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109. lilmax
4:06 PM GMT on May 06, 2007
lol pottery
108. pottery
11:37 AM AST on May 06, 2007
Good afternoom. Some interesting stuff going on. Tornados, unusual dry, a thing off Florida that shouldnt be there yet, fires and floods. Sounds like another misinterpretation of the Old Testament.
How are you guys going ?
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107. lilmax
3:56 PM GMT on May 06, 2007
Thanks Roman, if anythig happens this side of town I'll report it. We're under the "Slight Chance" of severe weather.
106. scottsvb
3:55 PM GMT on May 06, 2007
It will be mostly nontropical thru its lifetime...it will maybe pick up some tropical characteristics but never be all tropical in nature. The steering will be the ampliyfied ridge from the big trough over the central U.S..... the flow will become weak by early this week and the main jet goes to the north. question later in the week is how far south and west it will be to see if the eastern GOM surface ridge, will pick it up as a weak system and take it with its LLF or will it wait for the flow to become SE around the building bermuda surface ridge and take it NNW.
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105. Drakoen
3:55 PM GMT on May 06, 2007
Posted By: StormJunkie at 3:54 PM GMT on May 06, 2007.

scott, that surface high will block the low from moving north no? And is it not what is pushing the low South?


thats what i am saying. The high has nothing to do with its strength. It could gain tropical characteristics due to SST. And there shear is forcasted to drop quite dramtically. lets see what the NHC says about the system at 2:00 pm and then base our discussion of that.
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104. Drakoen
3:53 PM GMT on May 06, 2007
Posted By: scottsvb at 3:51 PM GMT on May 06, 2007.

OK maybe you confused me or something...the high in the NE is a surface high and it has nothing todo with this system in strength. There is a deep trough over the central U.S. and with that it amplifys the heights east of the Mississippi....taking anything down S to SW towards the SE coast or under 30N. The system will be cold core..but as it tries to pick up tropical characteristics....it will weaken....and when it does...it will maybe again move S with the LLF from the high in the eastern GOM by later Friday.


I am talking about the high controlling where the system goes. As of now, i don't think you can say definately that this system will be a cold core through its life. There are alot of things that have to happen.
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103. StormJunkie
3:52 PM GMT on May 06, 2007
scott, that surface high will block the low from moving north no? And is it not what is pushing the low South?
Member Since: August 17, 2005 Posts: 26 Comments: 15872
102. scottsvb
3:44 PM GMT on May 06, 2007
OK maybe you confused me or something...the high in the NE is a surface high and it has nothing todo with this system in strength. There is a deep trough over the central U.S. and with that it amplifys the heights east of the Mississippi....taking anything down S to SW towards the SE coast or under 30N. The system will be cold core..but as it tries to pick up tropical characteristics....it will weaken....and when it does...it will maybe again move S with the LLF from the high in the eastern GOM by later Friday.
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101. RL3AO
10:47 AM CDT on May 06, 2007
Heres the example of EF4 damage according to the NWS

EF4 damage picture
100. StormJunkie
3:42 PM GMT on May 06, 2007
Morning all ☺

Drak, it looks like the high is still buiding in fairly strong and continuing to push the low S. Not sure how long that will hold up though.

With these storms that meander out there, things are fairly fluid from my experience. Tracks change often when you have a system that is going to hang out in a general area for several days.

As for the NAM model, you can find it from the NCEP model analysis page in the links here. Most of the other most used model pages are there also.
Member Since: August 17, 2005 Posts: 26 Comments: 15872
99. Drakoen
3:43 PM GMT on May 06, 2007
I'm gonna leave, but i should be back in time for the 2:00 pm NHC discussion.
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98. Drakoen
3:40 PM GMT on May 06, 2007
Posted By: scottsvb at 3:39 PM GMT on May 06, 2007.

Drakoen... what high?


the current high pressure that is over the northeast.That will be the key factor as this system develops.
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97. plywoodstatenative
3:36 PM GMT on May 06, 2007
Yes, who did you report it to roman. Thats the question, I live in Broward as well and unless you are talking about yesterday mornings storm. I do not know any other time recently that we could have had a warning go up.
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96. scottsvb
3:38 PM GMT on May 06, 2007
Drakoen... what high?
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95. Drakoen
3:35 PM GMT on May 06, 2007
hmm so it looks like its gonna be a South Carolina storm then.. sighs. I still want to see what the high does... how strong it will be a the system develops. Whats the speed as it exits the northeast...
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94. RL3AO
10:35 AM CDT on May 06, 2007
This will be interesting. Especially if the low gets over the gulf stream for a few hours.
93. RL3AO
10:19 AM CDT on May 06, 2007
HurricaneRoman, did you report it to police or the NWS?
92. hurricane23
11:32 AM EDT on May 06, 2007
12z NAM.
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91. Drakoen
3:29 PM GMT on May 06, 2007
Posted By: seminolesfan at 3:28 PM GMT on May 06, 2007.

Drakoen-NOT same as rapid TROPICAL cyclogenesis!!!


i meant the transitionary period.
Anyone have the NAM link?
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90. seminolesfan
3:28 PM GMT on May 06, 2007
Link

Its the WRF under 12z on the right side!
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89. Tazmanian
8:23 AM PDT on May 06, 2007
wow this is all i can say 100% of down town Greensburg is gone and you saw the photos right??? this was no EF4 NO way this was a EF4 that hit Greensburg the winds in Greensburg most have been so strong that there are no longer stop lights on the poll evere thing is gone and if they make this a EF4 i will be mad that was no EF4 when i look at the photos i would call it a EF5 a strong EF5



Downtown Greensburg lies in ruins

has you can see this ues to be a stop light look how strong the wind most have been to do that the olny thing it did not take was the poll

lol



this was a EF5
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88. scottsvb
3:27 PM GMT on May 06, 2007
NAM model is a run off of the GFS...usally 6Z behind.. if the GFS changes on the 12z run...the Nam will follow...
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87. seminolesfan
3:26 PM GMT on May 06, 2007
Drakoen-NOT same as rapid TROPICAL cyclogenesis!!!
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86. Drakoen
3:26 PM GMT on May 06, 2007
Posted By: seminolesfan at 3:26 PM GMT on May 06, 2007.

The new NAM is up(12z). It's on the SC solution and not on your list of four. I guess that would make it 3-2; however they are not all the same run time. I'd wait until more 12z runs come out to compare apples to apples.


Can i have the link please?
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85. seminolesfan
3:23 PM GMT on May 06, 2007
The new NAM is up(12z). It's on the SC solution and not on your list of four. I guess that would make it 3-2; however they are not all the same run time. I'd wait until more 12z runs come out to compare apples to apples.
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84. scottsvb
3:24 PM GMT on May 06, 2007
hurricane23 if the system heads back more sw by later thurs and friday..its cause it will be weaker and go with the LLF from the surface ridge over the SE US. Not sure if you were thinking there was a upper ridge...cause there wont be! It may acquire LL tropical characteristics to call it subtropical storm Andrea...but its a wait and see....but it will take a few days.
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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.