Big Wind in the Windy City

By: Dr. Jeff Masters , 2:30 PM GMT on April 24, 2007

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Tornadoes hit the Plains again last night, and several people in rural Nebraska were injured when a tornado ripped through farmland in the western part of the state. The Storm Prediction Center has put a large area of the Plains under their Moderate Risk region for severe weather today. Wunderphotographer Mike Theiss chased the tornado that caused severe damage in Tulia, Texas over the weekend, and will be out chasing storms in the Plains today. Mike will be chasing frequently over the coming month, so be sure to tune into his blog for the latest!

Big wind in the Windy City
What would happen if a violent, long-track EF4 or EF5 tornado ripped through a densely populated urban area like Chicago? That was the question posed by tornado researcher Josh Wurman of the Center for Severe Weather Research in Boulder and three co-authors in a paper published in the January 2007 issue of the Bulletin of the American Meteorological Society. Their astonishing answer: damage of $40 billion and 13,000-45,000 people killed--the deadliest natural disaster in American history.

A tornado death toll in the ten of thousands seems outlandish when one considers past history. After all, the deadliest tornado in U.S. history--the great Tri-state Tornado of March 18, 1925--killed 695 people in its deadly rampage across rural Missouri, Illinois, and Indiana. That was before the advent of Doppler radar and the National Weather Service's excellent tornado warning system. In fact, there has not been a tornado death toll over 100 since 1953, the year the NWS began issuing tornado warnings. Chicago has been hit by one violent tornado. On April 21, 1967 a 200-yard wide F4 tornado formed in Palos Hills in Cook County, and tore a 16-miles long trail of destruction through Oak Lawn and the south side of Chicago. Thirty-three people died, 500 more were injured, and damage was estimated at $50 million.

The paper by Wurman et al., "Low-level winds in tornadoes and the potential catastrophic tornado impacts in urban areas" opens with an analysis of the wind structure of two F5 tornadoes captured on mobile "Doppler on Wheels" radar systems--the May 3, 1999 Bridgecreek-Moore tornado, which hit the southern suburbs of Oklahoma City, and the Mulhall, Oklahoma tornado of the same day, which moved over sparsely populated rural regions. The Bridgecreek-Moore tornado had the highest winds ever measured in a tornado, 302 mph. Winds of EF4 to EF5 strength (greater than 170 mph) are capable of completely destroying a typical home, and occurred over a 350 meter (1150 foot) wide swath along this tornado's path. The Mulhall tornado had weaker winds topping out at 245-255 mph, but had EF4 to EF5 winds over a much wider swath--1600 meters (one mile).

The F4 to F5 winds of the Bridgecreek-Moore tornado killed 36 people. Given the population of the area hit, between 1% and 3% of the people exposed to these winds died. The authors thought that this number was unusually low, given the excellent warnings and high degree of tornado awareness in Oklahoma's population. They cited the death rate in the 1998 Spencer, South Dakota F4 tornado that destroyed 30 structures and caused six deaths, resulting in a death rate of 6% (assuming 3.3 people lived in each structure). There are no studies that relate the probability of death to the amount of damage a structure receives, and the authors estimated crudely that the death rate per totally destroyed structure is 10%. This number will go down sharply if there is a long warning time, as there was in the Oklahoma tornadoes. If one takes the Mulhall tornado's track and superimposes it on a densely populated region of Chicago (Figure 1), one sees that a much higher number of buildings are impacted due to the density of houses. Many of these are high-rise apartment buildings that would not be totally destroyed, and the authors assume a 1% death rate in these structures. Assuming a 1% death rate in the partially destroyed high-rise apartment buildings and a 10% death rate in the homes totally destroyed along the simulated tornado's path, one arrives at a figure of 13,000-45,000 killed in Chicago by a violent, long-track tornado. The math can applied to other cities, as well, resulting in deaths tolls as high as 14,000 in St. Louis, 22,000 in Dallas, 17,000 in Houston, 15,000 in Atlanta, and 8,000 in Oklahoma City.


Figure 1. Wind speed swaths for the 1999 F5 Mulhall, Oklahoma tornado if it were to traverse a densely populated area of Chicago. Units are in meters/sec (120 m/s = 269 mph, 102 m/s = 228 mph, and 76 m/s = 170 mph). Winds above 170 mph usually completely destroy an average house, with a crudely estimated fatality rate of 10%, according to Wurman et al.. Insets x, y, and z refer to satellite photo insets in Figure 2. Image credit: Bulletin of the American Meteorological Society.


Figure 2. Aerial photographs from Google Earth of densely populated area of Chicago (insets x, y, and z from Figure 1) These areas contain mainly single-family homes, with housing units densely packed on small lots. A mixture of three-story apartments and single-family homes is typical across the Chicago metropolitan area and many older cities such as New York City and Detroit. At lower right is a photo of Moore, OK, showing lower density housing like the 1999 Bridgecreek-Moore tornado passed through.

How realistic are these estimates? Could a violent tornado really eclipse the Galveston Hurricane (8,000 killed) as this nation's worst natural disaster? The authors admit that their method of estimating deaths is crude, and considered death rates from only two storms to arrive at their estimates. I took a look at the fatalities from some other F5 tornadoes since 1991, and the death rates are highly variable (3% for the 1000 buildings destroyed by the 1998 Birmingham, AL tornado; 66% for the 41 buildings destroyed by the 1997 Jarrell, Texas tornado; 0% for the 66 buildings destroyed in the 1996 Oakfield, Wisconsin tornado; and 5% for the 350 buildings destroyed in the 1991 Andover, Kansas tornado). Based on these numbers, a 5% death rate may be more typical than the 10% death rate assumed in the Wurman et al. study. Violent tornadoes have hit downtown areas in the past, but have not affected nearly the number of structures as considered in the Wurman et al. study. The authors emphasize that even if their death rate estimates are off by a factor ten, a violent tornado in Chicago could still kill 1,300-4,500 people. The authors don't give an expected frequency for such an event, but I speculate that a violent tornado capable of killing thousands will probably occur in a major U.S. city once every few hundred years--or perhaps as long as 1000 years, considering that there have not been any F5 tornadoes in the U.S. since 1999.


Figure 3. Tornadoes to affect the Chicago area, 1950-2005. Background image credit: Google Earth. Tornado paths: Dr. Perry Samson.

Jeff Masters

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95. polarisa3
7:28 PM GMT on May 07, 2007
There was an F5 that hit the Chicagoland area back in 1990. The Plainfield tornado that destroyed parts of Plainfield, and Joliet. It was the strongest storm ever to hit the Northern Illinois area. This happens to be my hometown :)
94. TheCaneWhisperer
3:24 PM GMT on April 25, 2007
Thanks for the info 23, never really followed it that closely!
93. Skyepony (Mod)
2:15 PM GMT on April 25, 2007
Slumming throught the news wire~
We've seen the talk on lets replace Quikscat but in this article Hurricane center chief warns worse forecasts if satellite fails ~ in there this was said about Proenza..

At the same time, he strongly opposed a proposal to close any of the National Weather Service’s 122 offices around the nation or have them operate part time, saying “weather certainly doesn’t take a holiday.”

Is there a new propsosal??
Member Since: August 10, 2005 Posts: 227 Comments: 39455
92. hurricane23
1:53 PM GMT on April 25, 2007
Hey TheCaneWhisperer!

Basically when the SOI go's up it would indicate the possibilty of nina conditions and when it go's down it indicates nino conditions maybe present.

Here is a paragraph which could be of good help for you.SEE HERE

I would also like to point out that it is not useful to moniter it on a weekly basis but more on a 30-60 average.

Here is a piece from the lastest BOM update referring to the lastest drop not meaning to much.

The SOI on the other hand, has dropped below −10 during April thereby raising concerns about continued dry weather in eastern Australia. However, the SOI often shows increased monthly fluctuations at this time of year, so at this stage there is no longer-term significance in the SOI behaviour. There appears to be little chance of a return to El Niño conditions in 2007, with a continuation of neutral, or a switch to La Niña conditions, the more likely outcomes.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
91. TheCaneWhisperer
1:42 PM GMT on April 25, 2007
I am not very versed on the SOI 23, can you enlighten me a bit. I know what is means just not the effects of negative or positive SOI.
90. hurricane23
12:51 PM GMT on April 25, 2007
Morning everybody...

Again for those who have not seen or read the new ENSO update there forcasting Neutral to a very weak la nina this season.In my opinion we will see Neutral this hurricane season followed by a possible weak nina be late fall.

Here's part of there summary...

Equatorial Pacific sea-surface temperatures have cooled slightly during April, but remain close to average. The Trade Winds have been generally stronger than normal during recent months, while cloudiness in the western-central Pacific has been close to average for the past month. Overall, these ENSO indicators are neutral. The SOI on the other hand, has dropped below −10 during April thereby raising concerns about continued dry weather in eastern Australia. However, the SOI often shows increased monthly fluctuations at this time of year, so at this stage there is no longer-term significance in the SOI behaviour. There appears to be little chance of a return to El Niño conditions in 2007, with a continuation of neutral, or a switch to La Niña conditions, the more likely outcomes.

Complete ENSO out here
Member Since: May 14, 2006 Posts: 8 Comments: 13841
89. franck
12:47 PM GMT on April 25, 2007
TheCaneWhisperer...you're absolutely right about that. Pres is a puppet.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
88. TheCaneWhisperer
12:01 PM GMT on April 25, 2007
Posted By: JFLORIDA at 10:43 PM EDT on April 24, 2007.
WOW the Frontline tonight on Global Warming politics is frightening. The suppression of climate change data and the underwriting by oil, coal and gas producers of the deniers is Staggering.



Pirates! Let's boycot gas! ummm, darn, can't do that. Exxon Mobil seems to be front runner so I am going to stop using them. Oil change coming up too, :-(. That's too bad, Mobile 1 is good oil. Amazing how powerful money is! Who needs a president, the all mighty dollar controls this country!
87. MZT
11:44 AM GMT on April 25, 2007
For Charlotte, sometimes it's a bummer in the winter seeing the mountains capture all the snow.

But when these eastward moving systems are bringing tornadoes in the spring, the terrain is very helpful in breaking up their organization near the ground. We get tornadoes more from Nor'easters that are tracking inland, and sometimes from fast-forming afternoon thunderheads.

Member Since: September 24, 2005 Posts: 0 Comments: 793
86. sxwarren
11:18 AM GMT on April 25, 2007
"Downtown" tornadoes:

July 2nd 1997, supercells in SE Lower Michigan generated a tornado outbreak that included an F2 that cut through NW Detroit.

This area, including Highland Park and Hamtramack, has similar population and structural density to the areas around Chicago shown in the Google Earth shots. This F2 caused $100 million in damage and about 100 injuries but, officially, no fatalities. However, just to the NE, along the same path, a wedding party on the shore of Lake St. Clair had taken shelter in a gazebo. Five people died and eight others injured when the gazebo was blown into the water.
Member Since: October 29, 2006 Posts: 0 Comments: 103
85. vince1
9:50 AM GMT on April 25, 2007
In Denton county (just north of Dallas), one locale saw 10 inches of rain yesterday. O.o This severe weather is providing a blessing in disguise in that its erasing our recent 2-to-3 year drought.
Member Since: August 6, 2006 Posts: 0 Comments: 210
84. V26R
9:31 AM GMT on April 25, 2007
JFlorida, thats graph is showing just a really sharp cold front moving past that buoy, possibly with a Boomer near it too, or maybe just from the front giving you the gusty winds. If you notice now the pressure is rising too
so the cold front is past that buoys location
You probably get pressure drops and gusts of winds like that at your onland location when you get cold fronts moving through!
Member Since: July 20, 2006 Posts: 0 Comments: 1762
82. StoryOfTheCane
6:07 AM GMT on April 25, 2007
im not seeing anything go under 1008mb's
81. StoryOfTheCane
5:36 AM GMT on April 25, 2007
im not seeing the GFS development that 882 was talking about earlier, anyone want to enlighten me?
80. V26R
3:28 AM GMT on April 25, 2007
I feel a disturbance in the force
Member Since: July 20, 2006 Posts: 0 Comments: 1762
78. MZT
3:11 AM GMT on April 25, 2007
Seems kinda quiet here without STORMTOP. It's as if... people were just hanging around, talking about the weather, or something....
Member Since: September 24, 2005 Posts: 0 Comments: 793
77. hurricane23
2:55 AM GMT on April 25, 2007
Just read the lastest ENSO update and the possiblity remains that we will remain in neutral conditions.

There appears to be little chance of a return to El Niño conditions in 2007, with a continuation of neutral, or a switch to La Niña conditions, the more likely outcomes.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
74. hurricaneman23
2:36 AM GMT on April 25, 2007
is there a chance for some tropical development in the near future
73. weatherboykris
2:31 AM GMT on April 25, 2007
goodnight
Member Since: December 9, 2006 Posts: 125 Comments: 11346
70. weatherboykris
2:20 AM GMT on April 25, 2007
Really?It isn't a TS,a TD.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
68. MZT
1:56 AM GMT on April 25, 2007
I do remember the Canadian model, forecasting Alberto 7 days in advance last year.

But of course if a model continuously says a storm is coming, it will eventually be right! ;o)
Member Since: September 24, 2005 Posts: 0 Comments: 793
67. weatherboykris
1:54 AM GMT on April 25, 2007
We'll see what happens.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
66. KYhomeboy
1:52 AM GMT on April 25, 2007
I agree. If the runs are continuously showing some sort of development in the caribbean... it can be assumed that conditions there are becoming more favorable.
65. weatherboykris
1:48 AM GMT on April 25, 2007
Especially with run-to-run continuity.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
64. weatherboykris
1:48 AM GMT on April 25, 2007
Exactly.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
63. KYhomeboy
1:45 AM GMT on April 25, 2007
While looking at a 384 hour forecast, specific systems can't be pin pointed because of the forecast being so long term...BUT...they can often give clues as to what the overall trend is likely to be.
62. weatherboykris
1:44 AM GMT on April 25, 2007
It's still interesting.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
61. MZT
1:38 AM GMT on April 25, 2007
LOL - I hope you're not seriosly looking at 384 hour forecasts.

Anything more than 96 hours is a crapshoot.
Member Since: September 24, 2005 Posts: 0 Comments: 793
60. Skyepony (Mod)
12:57 AM GMT on April 25, 2007
NOVA Saved by the Sun is about to air on PBS EDT. All about solar power.
Member Since: August 10, 2005 Posts: 227 Comments: 39455
59. 882MB
12:52 AM GMT on April 25, 2007
and click on 384 hour!
Member Since: September 29, 2006 Posts: 0 Comments: 434
58. 882MB
12:51 AM GMT on April 25, 2007
Stormxyz, go to-http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/carib/gfs/12/model_l.shtml
Member Since: September 29, 2006 Posts: 0 Comments: 434
57. Stormxyz
12:45 AM GMT on April 25, 2007
hey 882mb or anyone else for that matter - when doing "runs" on the gfs, i forgot how to do it from last year. I got this link:
http://moe.met.fsu.edu/tcgengifs/

But just dont how to fill in the fields so that i get a full run all the way out, even to 2 weeks.

Any and all help would be apprecaited - im sure its quite simple once i realize how the easiest or most basic runs can be conducted. thanks again!
56. Acesover8s
12:10 AM GMT on April 25, 2007
We got small funnels dropping down in west palm beach. pretty cool
55. 882MB
11:43 PM GMT on April 24, 2007
Hey everybody, I heard a little earlier about WRMING SST'S well the GFS FOR THE PAST 2 RUNS HAS SHOWN DEVELOPMENT IN THE CARRIBEAN BUT WERE TO FAR OUT!
Member Since: September 29, 2006 Posts: 0 Comments: 434
54. KEEPEROFTHEGATE (Mod)
11:42 PM GMT on April 24, 2007
U AINT SEEN NUTTIN YET LATEST INFO INDICATES EXTREME WEATHER EVENT IS ABOUT TO SET UP EXPECT A SECOND WAVE OF STONGER VELOCITES TO SET UP WITH ABUNANT MOISTURE FLOW FROM WESTERN GOM LOOKS AS IF IT WILL GO BEYOND SEVERE TO ACHEIVE EXTREME THOSES HIGH SSTS IN WEST CAR AND GOM IS SUPPLING LOTS OF VAPOR COMBINE WITH GOOD SOUTHLY FLOW LOTS OF STORM CHASING TONIGHT.
Member Since: July 15, 2006 Posts: 178 Comments: 56141
53. chessrascal
11:23 PM GMT on April 24, 2007
lol

this is going to be a massive breakout!!
52. chessrascal
11:15 PM GMT on April 24, 2007
no one is here i guess
51. kellnerp
10:28 PM GMT on April 24, 2007
In Chicago it wouldn't be the people in structures that take the worst of it. Imagine a tornado going up the Stevenson Expressway during a rush hour. The Stevenson follows roughly the typical track of a tornado in the Chicago area. If this occurred there is simply nowhere to go fo those in vehicles. With the pelting rain and other visibility hindrances of a rush hour most people wouldn't know what hit them and even if they were listening on the radio would have no option. It appears at least one F4 did hit part of the Stevenson from the picture, but that might have been before it was constructed.

Another item is that Chicago buildings are mainly brick with flat roofs. Because they are so densely packed (frequently just enough room to walk between) they would tend to deprive the wind of a surface to "bite" into. This is not to say there wouldn't be a great deal of damage, but it would not be as great per square mile as that in a suburban sprawl with widely spaced stick built houses. I wonder if anyone has ever studied the boundary layer of tornadic winds with the ground?
Member Since: September 1, 2003 Posts: 0 Comments: 172
50. 1900hurricane
10:22 PM GMT on April 24, 2007
Everyone be sure to keep an eye on this map!

Member Since: August 2, 2006 Posts: 47 Comments: 11709
49. chessrascal
10:17 PM GMT on April 24, 2007
radar

KANSAS CITY RADAR LOOP. LOOKS LIKE A MAJOR OUTBREAKS ON THE WAY.
48. RL3AO
10:09 PM GMT on April 24, 2007
This looks like it will be an impressive outbreak.
47. chessrascal
10:02 PM GMT on April 24, 2007
TULSA RADAR

radar
46. chessrascal
9:57 PM GMT on April 24, 2007
radar

numerous hail cells on the Kansas City Radar
45. chessrascal
9:52 PM GMT on April 24, 2007
cool pic

cool pic from this website:Link

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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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