Plainfield Tornado
From Wikipedia, the free encyclopedia
| Date of tornado: | August 28, 1990 |
| Time: | 3:15 p.m. to 3:45 p.m. CDT |
| Rating of tornado: | F5 tornado |
| Damages: | $165 million |
| Fatalities: | 29 |
| Area affected: | Plainfield, Illinois, Crest Hill, Illinois, Joliet, Illinois |
|
|
|
The Plainfield Tornado was a devasting tornado that occurred on the afternoon of August 28, 1990. It formed from a supercell thunderstorm which initially formed in the vicinity of Janesville in south central Wisconsin and produced at least one tornado near Rockford, Illinois earlier in the afternoon. The principal tornado initially touched down just north of Oswego at about 3:15 pm CDT, a village about 10 miles (16 km) northwest of Plainfield. Traveling southeast, the tornado rapidly strengthened into a violent F5 tornado outside of Plainfield and tore through the city, killing 29 and injuring 350 people in the deadliest tornado event in the region since the Belvidere - Oak Lawn Tornado Outbreak of April 1967.
Contents |
[edit] Atmospheric conditions
For late August standards, August 28th was a very humid, very warm day. Temperatures reached into the low 90s Fahrenheit (about 11 degrees warmer than the normal of 79 degrees), but dewpoints soared into the upper 70s. The presence of such a high dewpoint did not necessarily predict a severe thunderstorm outbreak; the prior day, similar conditions existed in northern Illinois with the exception of a warmer mid-level atmosphere. A warmer atmosphere inhibits the rising of surface air through the atmosphere — a requirement for precipitation, in the form of humid surface air condensing in a cold atmosphere, to occur. This is known as a "capped" atmosphere.
The atmosphere on the 28th was significantly more unstable, although the wind fields (strong, but out of the west-northwest) were not suitable for tornadic development. As a result of the high dewpoint, CAPE values (Convective Available Potential Energy) were in excess of 8,000 J/KG; generally, values of 1,500 are considered to be moderately unstable, whereas values of more than 3,000 are a good indication of severe storms. The energy in the atmosphere required lift to initiate into thunderstorms; at this time, the LI (Lifted Index) was a number used to measure the overall amount of lift in the atmosphere. A LI value of -6 or below supports severe thunderstorm development, but during the day the LI value ranged from -12 to -14.
Conditions were ripe for severe thunderstorm development, and with both low level and high level steering winds from the west-northwest, the National Severe Storms Forecast Center issued a Severe Thunderstorm Watch for northern Illinois valid 1:30 p.m. through 8:00 p.m. CDT that night. The NSSFC predicted a derecho-type event for later that night as rapidly developing thunderstorms along a cold front in Wisconsin would be carried by the steering flow into the Chicagoland area. One of these storms developed supercellular characteristics south of Rockford, steering 30 to 40 degrees to the right of prevailing steering winds. By now, mid-level steering winds had begun to veer, causing a situation slightly more favorable for tornadic development. Once a tornado formed, the extreme instability contributed heavily to its rapid development into a one-half mile (.75 km) wide tornado.
[edit] Tornado touchdown and damage
In Kendall County, the supercell spawned an "average" F2 tornado near Oswego. Strengthening to an F5, the tornado travelled through Will County, moving into Plainfield, Illinois around 3:28 p.m. By 3:45 p.m., the tornado had directly struck Plainfield High School, killing a science teacher who was observing the tornado. The tornado then moved to Crest Hill, where it caused more F5 damage. A total of 29 people were killed.
The tornado weakened while entering the large city of Joliet, Illinois, dissipating after having traveled a distance of 16 miles (26 km).
[edit] Aftermath
[edit] Tornado preparedness
The Plainfield Tornado challenged both meteorologists and citizens in terms of tornado preparedness. Substantial safety measures were enacted in the years following the tornado; among these are frequent and regular tornado drills performed in schools.
After the tornado, meteorologists studying tornadic patterns in the area found that a major tornado (F3 or higher) strikes Will County about every 12 to 15 years. There have been no major tornadoes since 1990.
[edit] Deployment of NEXRAD
The development of NEXRAD (Next Generation Radar) contributed greatly to the ability of meteorologists to recognize tornadic activity. Where previous generations of radar would only show a severe storm, NEXRAD contained the ability to detect features inside the storm as small as the hook echo, a primary sign of tornadic formation. In addition, future revisions of NEXRAD radar were able to measure the relative velocity of a storm. The ability to see rotation inside a storm on both the microscale (tornadic) and mesoscale (supercellular) measurements has allowed forecasters to issue severe thunderstorm and tornado warnings in more timely fashion.
Partially in remembrance of the Plainfield tornado, the National Weather Service installed the next generation radar in nearby Romeoville. It replaced an older generation of radar further to the southwest in Marseilles.
[edit] Forecast criticism
In the months following the tornado, the National Weather Service was heavily criticized for providing no warning of the approaching tornado. Prior to 1990, the National Weather Service in Chicago was responsible for providing forecasts for the entire state of Illinois. As the Chicago office was overwhelmed with its workload, no warnings were issued by the office until 2:32 p.m. — nearly an hour after the first tornado was sighted southeast of Rockford. A second severe thunderstorm warning was issued almost an hour later at 3:23 p.m., but this provided no indication that a tornado was on the ground.
According to the Chicago Tribune, NWS Chicago had "the worst record in the nation" for issuing warnings for severe storms, only issuing warnings 24% of the time when a warning was justifiable. In addition, the office was concerned about issuing warnings for situations that were not necessarily severe. At some point after the 1990 tornado, the National Weather Service reduced the Chicago office's workload by creating an office in Lincoln, Illinois and allowing offices in the Quad Cities, St. Louis, Missouri, Indianapolis, Indiana and Paducah, Kentucky to issue forecasts for their respective areas.
[edit] Illinois' Tornado Alley
The Plainfield Tornado was the latest example in a continuing observation; that southwest areas of Chicagoland, and Will County in particular, are more prone to tornadic activity than counties to the north and east. Meteorologists have theorized that this is due to the stabilizing presence of Lake Michigan and the fact that Will County is closer to the main Tornado Alley than Chicago is, even if only by 40 miles (65 km). It is worth noting that examples of tornadoes in the city of Chicago itself do exist; one that heavily damaged portions of Oak Lawn in 1967 caused 33 deaths. [1]
[edit] See also
- List of tornadoes and tornado outbreaks
- Utica, Illinois Tornado Outbreak — a similarly unexpected tornado outbreak caused largely by small-scale changes in the surrounding meteorological environment.
[edit] References
- ^ National Weather Service via ComPortOne
- Brenner, Sue Anne, and Eric K Noji (1995). "Tornado Injuries Related to Housing in the Plainfield Tornado". International Journal of Epidemiology, vol 24, no 1, p 144-9.
- Fujita, T.T. (1991). "Plainfield tornado of 28 August, 1990". WRL Research Paper 234, University of Chicago, 25 pp.
- NOAA (May 1991). "The Plainfield/Crest Hill Tornado". Natural Disaster Survey Report.
[edit] External links
- Tornado Disaster -- Illinois, 1990 (CDC, MMWR 40(2); 33-36)
- Plainfield, IL Tornado 1990
- Plainfield Tornado History (Plainfield Public Library)
- Northern Illinois Storm Lab
- Reflections on the Plainfield tornado by Tom Skilling
