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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183. weatherboykris
6:13 PM GMT on May 06, 2007
Too soon to tell,louisianaboy.We don't even have a center yet!LOL
Member Since: December 9, 2006 Posts: 125 Comments: 11346
182. stormhank
6:09 PM GMT on May 06, 2007
HI all...whats latest thinking on system off SE coast? I saw couple models loop it n bring it into Ga//Fla coast?
Member Since: September 8, 2005 Posts: 0 Comments: 1386
181. pottery
2:11 PM AST on May 06, 2007
Hi Bama.
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180. louisianaboy444
6:11 PM GMT on May 06, 2007
forms i mean
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179. louisianaboy444
6:08 PM GMT on May 06, 2007
so if this storm falls it will continue southward toward florida then recurve out to sea?
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178. melwerle
6:09 PM GMT on May 06, 2007
Thank you Storm! Got it. :)

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177. Bamatracker
6:09 PM GMT on May 06, 2007
afternoon everyone!!!
Member Since: May 17, 2006 Posts: 6 Comments: 1367
176. weatherboykris
6:08 PM GMT on May 06, 2007
What you saying, eye?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
174. eye
6:06 PM GMT on May 06, 2007
lol, kris....good guess
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173. weatherboykris
6:06 PM GMT on May 06, 2007
There is still a HUGE amount of uncertainty right now,though.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
171. pottery
2:02 PM AST on May 06, 2007
We look forward to hearing from you on Wed. then, GAGuy, Batten down. It may come to pass...
Member Since: October 24, 2005 Posts: 0 Comments: 24260
170. weathersp
2:00 PM EDT on May 06, 2007
TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN MAY 06 2007

...DISCUSSION...

GULF OF MEXICO...
MODERATE TO STRONG RETURN FLOW CONTINUES TO DOMINATE THE GULF MAINLY W OF 90W WHERE A TIGHTER PRES GRADIENT EXISTS DUE TO LOWER PRESSURE OVER MEXICO. EARLIER QUIKSCAT PASS SHOWED SLY WINDS OF 15 TO 25 KT. AN UPPER RIDGE IS BUILDING ACROSS THE GULF AND IS SPREADING UPPER LEVEL MOISTURE/HIGH CLOUDS EWD INTO THE GULF ESPECIALLY W OF 90W. MOSTLY DRY MID TO UPPER AIR IS OVER THE ERN PORTION WITH NW FLOW ASSOCIATED WITH A STRONG UPPER TROUGH DIGGING OFF THE EASTERN SEABOARD. BACKDOOR FRONT ASSOCIATED WITH THIS TROUGH WILL AFFECT THE MIDDLE AND ERN GULF LATE TONIGHT INTO MON. STRONG HIGH PRES WILL FOLLOW THE FRONTAL BOUNDARY GIVING THE AREA MODERATE TO STRONG NE-E FLOW. THIS
WINDS ARE EXPECTED TO INCREASE TO 20-25 KT LATE TONIGHT.

CARIBBEAN SEA...
LIGHT TO MODERATE TRADES ARE BLOWING ACROSS MUCH OF THE BASIN DUE TO WEAK PRES GRADIENT OVER THE REGION. ALOFT...AN UPPER TROUGH IS DIGGING INTO THE WESTERN CARIBBEAN...WHILE AN UPPER HIGH CENTERED OFF NE SOUTH AMERICA EXTENDS A BROAD RIDGE OVER THE REMAINDER OF THE BASIN. THE RIDGE ALSO EXTENDS WWD FROM VENEZUELA TO COSTA RICA. SWLY WINDS ON THE WESTERN PERIPHERY OF THE RIDGE ARE TRANSPORTING ABUNDANT UPPER LEVEL MOISTURE/HIGH CLOUDS FROM THE EPAC ITCZ LOCATED JUST SOUTH OF PANAMA/COSTA RICA NEWD THROUGH THE CENTRAL AND NECARIBBEAN. UPPER DIFFLUENCE AND THE CLOSE PROXIMITY OF THE EPAC ITCZ ARE ENHANCING CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION OVER PANAMA...COSTA RICA AND THE SW CARIBBEAN. FAIRLY WEAK PRES GRADIENT WILL KEEP TRADES IN THE LIGHT TO MODERATE CATEGORY OVER THE NEXT COUPLE OF DAYS.

ATLANTIC...
GLOBAL MODELS HAVE CONTINUED TO COME INTO BETTER AGREEMENT REGARDING THE DEVELOPMENT AND ASSOCIATED FRONTAL STRUCTURE OF A STRONG LOW PRESSURE CENTER OFF OF THE SE COAST OF UNITED
STATES LATER TODAY THROUGH TUESDAY. THIS IS EXPECTED TO BRING SIGNIFICANT MARINE IMPACTS TO THE NW PORTION OF THE AREA INTO EARLY NEXT WEEK...INCLUDING GALE FORCE WINDS AND LARGE NLY SWELLS. SEVERAL MARINE ADVISORIES/WARNINGS ARE ALREADY IN EFFECT ALONG THE EASTERN COAST OF U.S FROM SOUTH FLORIDA TO BEYOND THE CAROLINAS. SHOWERS AND TSTMS HAVE INCREASED AHEAD OF THE BACKDOOR FRONT CURRENTLY EXTENDING FROM A 1012 MB SFC LOW NEAR THE OUTER BANK TO SOUTH GEORGIA. THIS CONVECTIVE ACTIVITY IS MOVING SOUTH CLIPPING NE FLORIDA. A SFC TROUGH REMAINS OVER THE W ATLC AND EXTENDS FROM 29N60W TO THE REGIONAL WATERS OF PUERTO RICO. THIS TROUGH HAS A 1012 MB LOW ATTACHED NEAR 28N60W. LATEST VIS SAT IMAGERY IS SHOWING A COUPLE OF LOW LEVEL SWIRLS ALONG THE TROUGH AXIS. MOST OF THE SHOWER ACTIVITY REMAINS WITHIN 80 NM E OF THE TROUGH WHERE MORE UPPER SUPPORT EXISTS...WITH DIFFLUENCE BETWEEN THE TROUGHING IN THE WRN ATLC AND RIDGING IN THE CENTRAL ATLC.

MUCH OF THE REMAINDER OF THE ATLC DISCUSSION AREA IS DOMINATED BY THE SRN PERIPHERY OF A QUASI-STATIONARY 1033MB SFC HIGH S OF
THE AZORES NEAR 35N28W. THIS IS GIVING THE AREA MODERATE TO FRESH TRADES AND MOSTLY FAIR WEATHER WITH ONLY PATCHES OF LOW LEVEL CLOUDS. THERE IS AN UPPER LOW NEAR 28N25W BUT IT DOES NOT APPEAR TO BE GENERATING ANY SIGNIFICANT WEATHER.



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169. weatherboykris
6:04 PM GMT on May 06, 2007
Here's what I'd bet on right now:



Maybe bottoms out at 998mb.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
168. Drakoen
6:05 PM GMT on May 06, 2007
GLOBAL MODELS HAVE CONTINUED TO COME INTO BETTER AGREEMENT
REGARDING THE DEVELOPMENT AND ASSOCIATED FRONTAL STRUCTURE OF A
STRONG LOW PRESSURE CENTER OFF OF THE SE COAST OF UNITED
STATES LATER TODAY THROUGH TUESDAY. THIS IS EXPECTED TO BRING
SIGNIFICANT MARINE IMPACTS TO THE NW PORTION OF THE AREA INTO
EARLY NEXT WEEK...INCLUDING GALE FORCE WINDS AND LARGE NLY
SWELLS. SEVERAL MARINE ADVISORIES/WARNINGS ARE ALREADY IN EFFECT
ALONG THE EASTERN COAST OF U.S FROM SOUTH FLORIDA TO BEYOND THE
CAROLINAS. SHOWERS AND TSTMS HAVE INCREASED AHEAD OF THE
BACKDOOR FRONT CURRENTLY EXTENDING FROM A 1012 MB SFC LOW NEAR
THE OUTER BANK TO SOUTH GEORGIA. THIS CONVECTIVE ACTIVITY IS
MOVING SOUTH CLIPPING NE FLORIDA. A SFC TROUGH REMAINS OVER THE
W ATLC AND EXTENDS FROM 29N60W TO THE REGIONAL WATERS OF PUERTO
RICO. THIS TROUGH HAS A 1012 MB LOW ATTACHED NEAR 28N60W. LATEST
VIS SAT IMAGERY IS SHOWING A COUPLE OF LOW LEVEL SWIRLS ALONG
THE TROUGH AXIS. MOST OF THE SHOWER ACTIVITY REMAINS WITHIN 80
NM E OF THE TROUGH WHERE MORE UPPER SUPPORT EXISTS...WITH
DIFFLUENCE BETWEEN THE TROUGHING IN THE WRN ATLC AND RIDGING IN
THE CENTRAL ATLC.
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167. FTmyersZ
2:01 PM EDT on May 06, 2007
Conditions at 41001 as of
(12:50 pm EDT)
1650 GMT on 05/06/2007:
Unit of Measure: Time Zone:
Click on the graph icon in the table below to see a time series plot of the last five days of that observation.

Wind Direction (WDIR): S ( 180 deg true )
Wind Speed (WSPD): 23.3 kts
Wind Gust (GST): 31.1 kts
Wave Height (WVHT): 5.6 ft
Dominant Wave Period (DPD): 5 sec
Average Period (APD): 4.6 sec
Atmospheric Pressure (PRES): 29.81 in
Pressure Tendency (PTDY): -0.10 in ( Falling Rapidly )
Air Temperature (ATMP): 64.6 F
Water Temperature (WTMP): 68.5 F
Dew Point (DEWP): 63.7 F
Combined plot of Wind Speed, Gust, and Air Pressure
Member Since: August 26, 2005 Posts: 0 Comments: 60
166. melwerle
6:01 PM GMT on May 06, 2007
Hey Storm - still no mail. Are you sending it to the right address? I usually don't have an issue with yahoo. Can you cut and paste to my email here?
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164. weatherboykris
6:00 PM GMT on May 06, 2007
I'll wait until they call it an invest pottery.Then they'll run the NHC models on it.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
163. pottery
1:57 PM AST on May 06, 2007
OK Kris.
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162. melwerle
5:55 PM GMT on May 06, 2007
You're da man, StormW! I'm waiting on it - will keep checking.
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161. Drakoen
5:52 PM GMT on May 06, 2007
Posted By: scottsvb at 5:50 PM GMT on May 06, 2007.

I will agree with the ECMWF,nogaps,Ukmet and even some of the GFS.... At first the storm will be strong..but nontropical...a gale center....but as it slowly picks up some tropical characteristics...it will weaken...cause it wont be a non tropical system as its in transition....then as it comes close to Floridas NE coast and St Augustine...the LLC will seperate from the mid and upper low and be on its west side and get pushed sw between the mid and upper low now to its E and the weak ridge over the NE gulf of mexico. This is the atmospheric synopsis.


Sounds interesting. I wanna hear, not that i'm saying your wrong, what the NHC has to say, cause they are the people who know what they are talkign about. I will agree with the fact that it will most likely not be a MID-South Florida storm as the high will weaken as it moves to the west.
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160. weatherboykris
5:55 PM GMT on May 06, 2007
Posted By: pottery at 5:49 PM GMT on May 06, 2007.

Still sounds a bit vague, Kris.
Whats your prediction ??



Far too early for me to throw out a forecast.We don't even have a low yet.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
157. Thundercloud01221991
5:50 PM GMT on May 06, 2007
SEVERE THUNDERSTORM WATCH for florida
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156. EP78852
5:50 PM GMT on May 06, 2007
SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 244
NWS STORM PREDICTION CENTER NORMAN OK
150 PM EDT SUN MAY 6 2007

SEVERE THUNDERSTORM WATCH 244 IS IN EFFECT UNTIL 800 PM EDT
FOR THE FOLLOWING LOCATIONS

AMZ454-550-555-610-630-650-651-GMZ656-657-830-850-853-856-
070000-
/O.NEW.KWNS.SV.A.0244.070506T1750Z-070507T0000Z/

CW

. ADJACENT COASTAL WATERS INCLUDED ARE

COASTAL WATERS FROM ST. AUGUSTINE TO FLAGLER BEACH FL OUT 20 NM

COASTAL WATERS FROM FLAGLER BEACH TO COCOA BEACH FL OUT 20 NM

COASTAL WATERS FROM COCOA BEACH TO JUPITER INLET FL OUT 20 NM

LAKE OKEECHOBEE

BISCAYNE BAY

COASTAL WATERS FROM JUPITER INLET TO DEERFIELD BEACH FL OUT 20 NM

COASTAL WATERS FROM DEERFIELD BEACH TO OCEAN REEF FL OUT 20 NM

COASTAL WATERS FROM CHOKOLOSKEE TO BONITA BEACH FL OUT 20 NM

COASTAL WATERS FROM EAST CAPE SABLE TO CHOKOLOSKEE FL OUT 20 NM

TAMPA BAY WATERS

COASTAL WATERS FROM TARPON SPRINGS TO SUWANNEE RIVER FL OUT 20 NM

COASTAL WATERS FROM ENGLEWOOD TO TARPON SPRINGS FL OUT 20 NM

COASTAL WATERS FROM BONITA BEACH TO ENGLEWOOD FL OUT 20 NM

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 244
NWS STORM PREDICTION CENTER NORMAN OK
150 PM EDT SUN MAY 6 2007

SEVERE THUNDERSTORM WATCH 244 IS IN EFFECT UNTIL 800 PM EDT
FOR THE FOLLOWING LOCATIONS

FLC001-009-011-015-017-021-027-035-043-049-051-053-055-057-061-
069-071-075-081-083-085-086-087-093-095-097-099-101-103-105-107-
111-115-117-119-127-070000-
/O.NEW.KWNS.SV.A.0244.070506T1750Z-070507T0000Z/

FL
. FLORIDA COUNTIES INCLUDED ARE

ALACHUA BREVARD BROWARD
CHARLOTTE CITRUS COLLIER
DESOTO FLAGLER GLADES
HARDEE HENDRY HERNANDO
HIGHLANDS HILLSBOROUGH INDIAN RIVER
LAKE LEE LEVY
MANATEE MARION MARTIN
MIAMI-DADE MONROE OKEECHOBEE
ORANGE OSCEOLA PALM BEACH
PASCO PINELLAS POLK
PUTNAM SARASOTA SEMINOLE
ST. LUCIE SUMTER VOLUSIA
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155. melwerle
5:50 PM GMT on May 06, 2007
Hey Storm! - I didn't get your update... :(

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154. scottsvb
5:45 PM GMT on May 06, 2007
I will agree with the ECMWF,nogaps,Ukmet and even some of the GFS.... At first the storm will be strong..but nontropical...a gale center....but as it slowly picks up some tropical characteristics...it will weaken...cause it wont be a non tropical system as its in transition....then as it comes close to Floridas NE coast and St Augustine...the LLC will seperate from the mid and upper low and be on its west side and get pushed sw between the mid and upper low now to its E and the weak ridge over the NE gulf of mexico. This is the atmospheric synopsis.
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152. pottery
1:46 PM AST on May 06, 2007
Still sounds a bit vague, Kris.
Whats your prediction ??
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151. Skyepony (Mod)
5:44 PM GMT on May 06, 2007
The 12Z runs look much more promising for rain in FL & GA
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149. melwerle
5:42 PM GMT on May 06, 2007
So...sitting here in Savannah - safe bet that we're going to get SOMETHING out of this and by when? Just wondering whether to break out the lifejackets.
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148. weatherboykris
5:37 PM GMT on May 06, 2007
NOGAPS:Heads into Florida
UKMET:Also into Florida
GFS:Near miss,remnents move south into FL after Georgia landfall.
NAM:Essentially the same as the GFS,but has te system meandering off SC at the end of it's run,future uncertain.
CMC:Near NC at the end of it's run.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
147. pottery
1:38 PM AST on May 06, 2007
My weather now ( Trinidad )
91 f
52 % humid.
98 F with the heat index

This is not what a tropical island is supposed to be man.
I'm running out of beers !!!!!!!!!!!!
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145. weatherboykris
5:36 PM GMT on May 06, 2007
More of the global models show this coming close to Florida.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
144. HurricaneKing
1:34 PM EDT on May 06, 2007
It's bad that with a north east wind the tide is not up. It's back to normal water level. Everything has been running below normal. (Sorry wrong blog but still has to do with the storm anyway.)
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143. Thundercloud01221991
5:34 PM GMT on May 06, 2007
already the cloud temps are dropping indicating stronger storm
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142. pottery
1:30 PM AST on May 06, 2007
Yeah, with the shear dropping off so quickly,the system could gain some height fast.
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141. Thundercloud01221991
5:28 PM GMT on May 06, 2007
The sheer in that area has dropped 20 kts in the last 24 hours
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139. whirlwind
5:22 PM GMT on May 06, 2007
Well now..what do we have here... an exciting season is in store for us? Maybe a makeup for the boring '06. Wasnt 2005 also when a tropical storm was named earlier than normal...well eyes wide open
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138. pottery
1:21 PM AST on May 06, 2007
Exactly so, Skye. And on the down-current side of the Stream, they will likely be smaller.
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136. pottery
1:09 PM AST on May 06, 2007
I met a wave a few years ago, 6 miles north of Tobago, while fishing with friends. It was rough and windy, typical dry-season. Suddenly, the boat was in shade for the first time that day, and the wave that caused the shade was over us. We turned into it, oppened the throttle full, and managed to punch through the crest which was falling over. The consensus on board was 22 feet. The drop into the hole behind the wave almost sank us because we landed transom-first. On one fell out, I cant explain how. And the boatstayed afloat because most of the water sloshed out over the transom on the next wave ( which was not as big )
Scared the 4 of us to silence for a long time while we put the boat back together.
Dont want to do that again.........
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135. Skyepony (Mod)
5:11 PM GMT on May 06, 2007
pottery~ Must be why the largest waves are forecasted over the gulf stream.
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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 )
Member Since: October 24, 2005 Posts: 0 Comments: 24260

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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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