National Weather Service United States Department of Commerce

Plainfield Tornado

 

The Facts and Statistics

     Between 3:15 p.m. and 3:45 p.m. CDT on August 28th, 1990, a violent F5 tornado ripped through Kendall and Will counties taking the lives of 29 people and injuring 350. The tornado left a 16.4 mile-long damage path which ranged from 600 yards to a half a mile in width. An estimated total of $160 million dollars in damages was added up with a total of 470 homes destroyed and 1000 damaged.

     Before the Enhanced Fujita Scale was put in use in 2007, the tornado damage was assessed by using the Fujita Scale. On the Fujita Scale, an F5 tornado has estimated wind speeds of 261-318 mph and is defined as having incredible damage in which strong frame houses can be leveled and swept off of foundations, automobile-sized objects can be lifted up into the air, and trees are usually debarked.

Fujita Scale Before 2007

Not only was this F5 tornado disastrous, it was also very unusual for several reasons:

  • The Plainfield tornado was the first ever tornado greater than an F3 rating, since records began in 1950, to occur during the month of August in the state of Illinois.
  • It was the second killer tornado since 1950 to occur during the month of August in Illinois.
  • 25 years later this tornado remains the only F5/EF5 rated tornado documented in the United States during the month of August.
  • The tornado had low clouds and rain surrounding it, making it difficult to see. Because of this, no known photographs or videos of this tornado exist.
  • The tornado approached from the northwest; most tornadoes approach from the southwest.

 

The Meteorology Behind the Tragedy

     The atmospheric conditions that spawned this deadly storm were typical of those which lead to most cases of severe weather. An upper-level shortwave trough was moving through the Great Lakes area, while below a cold front was forecast to push its way south through northern Illinois.

Surface map at 2 pm August 28, showing the cold front moving toward northern Illinois and the warm, moist air ahead of the front.
Surface map at 2:00 p.m. CDT August 28, showing the cold front moving toward
northern Illinois and the warm, moist air ahead of the front.

 

     The necessary recipe of moisture, instability, a source of lift and wind shear were all present. However, one important ingredient for tornadoes appeared to be missing: a sharp change in wind speed and direction in the lower levels of the atmosphere specifically. Deep layer shear was definitely considerable, with strong upper-level winds supportive of multicell storms with damaging winds and large hail. Without low-level shear, however, the data suggested that tornadoes would be only a remote possibility. At 10:00 a.m., the National Severe Storms Forecast Center (NSSFC) in Kansas City, Missouri (predecessor to the Storm Prediction Center, or SPC of Norman, Oklahoma) upgraded their severe thunderstorm outlook for northern Illinois from a Slight to a Moderate Risk, suggesting a greater coverage of damaging storms. At 1:28 p.m., NSSFC issued a Severe Thunderstorm Watch for portions of northern Illinois.

Sounding taken at Peoria at 7 pm on August 28.
The sounding taken at Peoria at 7:00 p.m. CDT on Aug 28 shows large instability and 50kt winds at
mid-levels of the atmosphere, which contributed to the favorable conditions for supercells.

 

     After thunderstorms began to develop near the central Illinois and Wisconsin border around noon, conditions increasingly began to favor supercells. CAPE (Convective Available Potential Energy) values rose from 4000 J/kg across much of northern Illinois to an incredible 7000 J/kg by 3:00 p.m., giving thunderstorms explosive energy. The cold front could be seen almost exactly crossing the state border at this time, with the high values south representative of very warm temperatures in the mid to upper 90s and oppressive dew points reaching the upper 70s.

Convective Available Potential Energy (CAPE) for August 28
CAPE values for August 28

 

     Despite the continued lack of strong low-level shear, the impressive parameters for supercell growth allowed one storm to quickly produce one or two brief tornadoes near Pecatonica and Seward, Illinois, just west of Rockford at 1:42 p.m. This occurred shortly after the NSSFC issued a Severe Thunderstorm Watch for the area at 1:28 p.m. As a dominant storm emerged later and ventured further into extreme instability and strong shear, it exploded to a height of over 65,000 feet and displayed classic supercell behavior, including a hook echo and southeast movement to the right of the upper-level winds that would normally steer it. This shift brought the storm through DeKalb and Kane Counties as it dealt strong winds and a swath of golf ball to tennis-ball sized hail. A map of the heavy precipitation that resulted serves as a “radar image” of the storm’s path.

Accumulated Precipitation - August 28
A map of the heavy precipitation that resulted from the severe thunderstorm shows the storm’s path.

     

     As this storm continued to build, a change in low-level winds was observed. Once generally northwest, surface winds quickly backed to the southwest. With surface winds out of the southwest and the upper-level winds from the northwest, the change in wind direction allowed nearly 90 degrees of directional shear with height; more than necessary for rotating storms and now perhaps a tornado.

Vector Wind for August 28
Surface Winds on August 28 at 100 pm CDT

 

     Unfortunately, those few degrees may have been all that was necessary for the devastation caused on this day. The supercell first dropped four separate brief tornadoes in rural southern Kane County, but after these attempts it was able to fully realize the wind energy it had been born into and formed an extremely powerful tornado near Oswego in Kendall County. A sequence of radar scans shows this storm’s full evolution.

 

Series of radar images from 2:27 pm through 3:49 pm. Picture from the Natural Disaster Survey Report.
Series of radar images from 2:27 p.m. through 3:49 p.m. CDT showing a
pronounced hook echo as the storm moved into northwestern Will County.

Photo from the Natural Diaster Survey Report.

 

Visible GOES satellite images showing the development of the tornadic thunderstorms.
Visibile GOES images showing the development and progression of the tornadic thunderstorms
across northern Illinois at (a) 12:46 pm CDT; (b) 1:46 pm CDT; (c) 2:46 pm CDT; and
(d) 3:46 pm CDT on the afternoon of August 28.

Photo from the Natural Disaster Survey Report.

 

     The tornado reached its highest strength from 3:15 p.m. to 3:45 p.m. as it moved from Kendall County into northwestern Will County and through the communities of Plainfield and Crest Hill. Despite the tornado finally dissipating in Joliet, the supercell produced damaging winds through Kankakee County and on into Indiana. Overall, this one deadly storm caused nearly continuous damage and took many lives over northern Illinois for 4-½ hours straight.

 

Tornado and Severe Thunderstorm Event Database for August 28
SPC event database for August 28

 

 

The Progress in 25 Years

     With all the tools available to any forecaster today, such a storm and such a tragedy would not likely come without warning. Since this deadly tornado, many aspects of meteorology have revolutionized the way we “see” dangerous weather coming.

Modeling: Within the science of computer programming, the practice of numerical modeling has grown from almost nonexistent to being a vital part of the forecasting process.

  • In 1990, few computer models existed and those that did were not nearly as advanced as they are today.
  • Now, numerous, highly complex models including the GFS (Global Forecast System), the ECMWF (European Model), the NAM (North American Mesoscale), the RAP (Rapid Refresh), and the HRRR (High-Resolution Rapid Refresh) can provide insight into weather conditions, including those favorable for severe weather hours, days, and even a week in advance.

Radars with Modelling
Radar Models

 

Observing: The observation of current weather conditions has grown from spotty and infrequent to dense and continuous. Now, ASOS (Automated Surface Observing System) stations cover the country, and “mesonets” are being created that monitor subtle changes in very specific locations, providing exceedingly high spatial and temporal data.

ASOS
Automated Surface Observing System

 

Monitoring: Weather Radar has also become increasingly more effective in “seeing” through the inner workings of thunderstorms.

  • In 1990, the NWS Chicago radar used 1974 technology which could only tell us the intensity of precipitation, leading us to infer storm types based on patterns. Warning forecasters, who were remotely located from the radar site, could only view basic data on a TV monitor, and needed to have details of what the radar operator was seeing relayed to them through radar summary products or by phone.
  • The current NWS Chicago radar, which is located at the Weather Forecast Office, is more powerful with much higher resolution. Thanks to Doppler capability, it can detect motion within a storm, allowing us to know if and where it is rotating or showing signs of producing a tornado. In addition, it features Dual-Polarization technology, which can distinguish between rain, hail, ice, snow and other material, and in some cases can serve as an alert that a tornado is on the ground by detecting debris!

Dual Polarization Radar
Dual Polarization image

 

Spotting: With increasing awareness of severe weather, more people are willing to learn how to prepare themselves.

  • In 1990, the NWS was able to run spotter training sessions that taught just over 1000 people how to recognize severe storms. On August 28th, however, no organized spotter networks were activated, thus no reports of wind damage, hail or tornadoes were received by the Chicago NWS office until after the worst had occurred. Storm chasers were able to observe a wall cloud, hail and high winds through rural DeKalb and Kane Counties, but they could not get ahead of the storm to see the tornado form. Without cell phones, their observations could not be relayed to the NWS, who in turn had little or no communications with emergency management and law enforcement in Kane, Kendall and Will Counties prior to or during the storm. The first report of a tornado was received as it dissipated in Joliet, after the damage had been done.
  • Now, the Chicago NWS trains nearly 3,000 people a year in spotting, usually between February and April to prepare for severe weather season. An all-day severe weather training seminar is conducted every year by DuPage County Office of Homeland Security and Emergency Management, College of DuPage, and NWS for dedicated spotters and emergency management. Not only do spotters now have a variety of ways to easily report severe weather and their location in real-time, but live video streaming is becoming increasingly popular amongst the spotter and storm chaser community. Spotter training now emphasizes safety precautions, the importance of a weather-ready plan and how to receive weather information. It also demonstrates how to observe specific cloud features indicative of a severe storm or the possibility of a tornado, and how to report any information so that warnings come sooner.

 

Warning: With meteorology’s overwhelming advancements it is now possible to know with greater accuracy who to warn, and warn people earlier when the few extra minutes matter most.

  • Before, entire counties would be placed under blanket Tornado Warnings which provided little in the way of tornado impact information. These warnings were first relayed to emergency management, law enforcement and the media by radio and wire services. The public received these warnings through two NOAA Weather Radio stations, one in Rockford and one in Chicago.
  • Now, all warnings are relayed almost instantaneously via satellite communications, and eleven NOAA Weather Radio transmitters across northern Illinois and northwest Indiana provide coverage to nearly 100 percent of the population. Radio broadcasts contain coded information that can trigger radios for specific types of alerts for specific counties. Tornado warnings, such as those issued for the devastating tornadoes that impacted Rochelle and Fairdale, Illinois on April 9th, 2015, distinguish between tornadoes that are “Radar indicated”, “Radar confirmed”, “spotter confirmed” or “law enforcement confirmed”, include cities and other locations in the path and the estimated time they will be impacted, and uses strategic wording to convey the damage potential, from “Considerable” to “Catastrophic”. An example from April 9th, 2015 is shown below.

Text of Rochelle warning
Text of Rochelle Tornado Warning from April 9, 2015

 

Communicating: Communication methods, frequency and availability have changed dramatically.

  • In 1990, the slow process of reporting and relaying information was sometimes not enough, and unfortunately for some the warnings came too late.
  • Now, in addition to radio and television, a plethora of methods of communication have emerged that allow for a redundancy in communication that reaches as many people as possible.
    • The NWS has a much closer and more effective relationship with county and community emergency management.
    • To help warn large groups of people more quickly, the Department of Homeland Security, Department of Education, and NOAA have teamed up to provide weather radios to every school in the country.
    • With the significant advancements in mobile technology, a large percentage of the population can receive and communicate warnings instantly by cell phone or other mobile device. The WEA (Wireless Emergency Alerts) system, a joint cooperation by the FCC and FEMA, now pushes Tornado and Flash Flood Warnings straight to cellular devices no matter their volume or notification settings.
    • Online social networks such as Facebook and Twitter ensure warnings reach hundreds or thousands of people in minutes not to mention serves as a growing source of ground truth of the impact a storm is having. In addition to satellite, radio, cellular and internet feeds, NWS Chicago made extensive use of social media, such as Facebook and Twitter, to convey the high tornado potential on April 9th, 2015.

 

Example of Social Media
Example of Social Media Post

 

 

The Bottom Line: Is Chicago Prepared?

Despite the advances in science, technology, communications, and education, the Chicago metro area is still vulnerable to significant and potentially devastating severe weather events.

  • The Plainfield Tornado was 25 years ago. There has not been a violent F4/EF4 or F5/EF5 tornado in the Chicago metro area since 1990. That means an entire generation of citizens has never experienced a major tornado disaster in the metro area. Many people have moved to northeast Illinois and northwest Indiana from other parts of the country, or other parts of the world, and may not be familiar with Chicago’s history of violent tornadoes. Many people still believe the myths that tornadoes can’t hit urban areas or will be stopped by the cool water of Lake Michigan.
  • The truth is tornadoes have occurred in the heart of other major cities in recent years, including Atlanta, Fort Worth, Salt Lake City, Nashville, and Miami. Tornadoes have struck within the city limits of Chicago in the past. Tornadoes have occurred at or near the lakefront as recently as August 2nd, when a tornadic waterspout (a tornado over water) occurred just offshore of North Chicago, spawned from the same thunderstorm that produced an EF-1 tornado over central Lake County, Illinois. In 2006, a tornado occurred briefly at the Loyola University campus and moved out over Lake Michigan as a waterspout.
  • Despite the high speed communications available, many people still rely on tornado sirens – which are designated as outdoor warning systems and not meant to be heard indoors. Also, as the population of the metro area grows and spreads further out, more people are in harm’s way. The truth is that large violent tornadoes have struck the Chicago metro area in the past, and they will again. It is only a matter of time. We now have the tools, the communications, and the partnerships with emergency management and the media to effectively warn people when the big one strikes.
  • Even with all of the advances in the severe thunderstorm and tornado warning process and the abundant communication resources available today, people still need to take personal responsibility to plan, practice, monitor and act.

 

Plan: Develop a plan for your circumstances (home, school, ball park, business, etc)

  • Know the threats associated with your situation (consider lightning, tornado, hail, snow storm, extreme heat…)
  • Address each threat as it applies to you (consider time of day, kids at school or home alone, parents working, shift change at work…)
  • Go to the lowest floor, maximize walls, minimize windows: Safest place is in an underground shelter or basement under sturdy furniture; if not available then an interior room on the lowest floor away from windows. Put as many walls between you and the outside as possible. In a high rise, get into an interior room with no windows. Mobile homes are not safe during tornadoes. Abandon mobile homes and go to the nearest sturdy building or shelter immediately.

 

Practice: Run through your plan periodically, like a fire drill

  • How much time do you need to reach shelter?
  • Does everyone know their role?
  • Re-evaluate your plan

 

Monitor: If there is a risk of severe weather, monitor the weather!

  • Designate a weather watcher (especially for schools, businesses). This person pays attention to the weather.
  • Check the Hazardous Weather Outlook each day; monitor for watches and warnings - If there is a threat for storms, monitor radar; “If Thunder Roars, Go Indoors” and check for warnings; if a watch is in effect and you hear thunder, check for warnings.
  • Have multiple ways to receive warnings: NOAA Weather Radio, WEA messages, www.weather.gov/chicago, local media, apps or subscriptions to an alerting service (www.weather.gov/subscribe)
  • NOAA Weather Radio is the quickest way to be alerted to a warning and can wake you up in the middle of the night

 

Act: Be proactive, if threatening weather approaches or warnings are issued, activate your plan.

  • How will you let everyone know the plan is being initiated?
    While none of us like to be inconvenienced, especially by weather, dropping everything and seeking shelter is essential to surviving a tornado whenever a warning is issued. If a watch is in effect, you want to be able to get to a storm shelter within minutes.

 

To see our review of the Plainfield tornado on the 20th year anniversary, visit https://www.weather.gov/media/lot/newsletters/summer2010rev1.pdf.

For more information on how to be prepared for severe weather, visit https://www.weather.gov/lot/severeprepare.