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Fall 2006 Volume 4 Issue 3 Serving the people of north central and northeast Severe Storms Provide Sobering Reminder The storms that struck northern Illinois and Chicagoland on Friday, September 22 were a vivid reminder of how vulnerable we are to a major tornado. During the Friday afternoon rush hour three distinct “supercell” thunderstorms tracked northeast across the west and northwest suburbs, north shore, and northern sections of the city. Each of these storms exhibited rotation during their lifetimes and occasionally produced funnel clouds. We were extremely fortunate none ever produced a tornado touchdown. NWS meteorologists are still investigating the event to determine why this was so. Preliminary research shows the lack of a touchdown may have been tied to slightly insufficient low level moisture in the atmosphere. None the less torrential rainfall, damaging wind gusts, and hail pelted neighborhoods as the storms moved through. Traffic came to a dead stop for up to 45 minutes on the tollway and air traffic shut down at O’Hare. All of this serves as a sobering reminder of how at risk we humans remain to the natural perils of the planet on which we live. As meteorologists our goal is to provide advance warning of any hazardous weather event so people may take precautions to protect themselves and their loved ones. The United States has the most sophisticated Doppler radar network and storm spotting networks critical to identifying and tracking severe storms and tornadoes. We also have the most advanced research and daily tracking of atmospheric conditions that identify and diagnose atmospheric conditions that contribute to producing severe weather. Today about 81 percent of all tornadoes in this country are preceded by a warning, and the average lead time of that warning is about 13 minutes. Now the rest is up to you. When a tornado develops you’ll likely only have a few minutes to react. What will you do? We each have a personal responsibility for our own safety. Keeping ourselves educated and advised is part of that responsibility. Have a trusted source you can turn to for instant weather information. The web site www.weather.gov/chicago is one option. Weather forecasts continue to become more accurate, but to take most advantage of this accuracy we suggest you check the weather four times a day, once when you start your day, again at lunch, again around the dinner hour, and again before you go to sleep. If a risk of severe weather is mentioned in the forecast, maintain higher awareness and stay tuned for later forecasts and possible warnings. Consider adjusting your routine to better enable you to get to a place of shelter should the need arise. With some extra planning and preparedness you can prevent yourself from becoming a weather victim.
A Study of the Chicago Area's Significant Tornadoes For the purpose of this study, a significant tornado is defined as being rated F2 or greater, or any tornado that has caused fatalities or injured at least 10 people. Weaker tornadoes (F0 and F1) are more common but not as well documented as strong (F2 and F3) and violent (F4 and F5) tornadoes, especially before about 1950. The significant tornadoes account for most of the deaths, injuries, and property damage from tornadoes. The Fujita scale, or F scale, estimates wind speeds based on damage intensity, where F0=40-72 mph, F1=73-112 mph, F2=113-157 mph, F3=158-206 mph, F4=207-260 mph, and F5=261-318 mph. The F scale is determined by conducting ground and air surveys of the damage path. The F scale was developed in the 1970s and was later applied to historical data, based on written accounts and photographs of tornado damage. Therefore the F scale ratings are subjective and may not accurately reflect the wind produced by the tornado. The F scale will be replaced by a new Enhanced F scale beginning February, 2007. Estimated wind intensity with the scale will be adjusted, but the historical database will not change. To learn more about the enhanced F scale, go to http://www.spc.noaa.gov/efscale/. Sources for the data in the study include StormData, the Storm Predication Center, and Significant Tornadoes 1680-1991 written by Tom Grazulis. For the purpose of this study, the Chicago area is defined as McHenry, Lake, Kane, DuPage, Cook, Kendall, Will, and Lake (IN) counties.
Some facts about Chicago's Significant Tornadoes
F-Scale Distribution of Significant Tornadoes
F2 tornadoes were most prevalent, while there were about a dozen F3 and F4 tornadoes between 1855 and 2006. Only one F5 tornado ever crossed the Chicago area. Monthly Distribution of Significant Tornadoes
Most of the tornadoes occurred in the spring, between March and June. The drop off is rather significant during the middle of summer, while late summer and fall is another, yet smaller peak. Surprisingly, there have been nearly as many significant tornadoes in November as in July. Diurnal Distribution of Significant Tornadoes
For the purpose of this study, the hour indicated is the hour in which the tornado began. For example, if a tornado began at 155 PM and ended at 205 PM. It will be considered as occurring in the 100 PM hour. Time is local time. Most tornadoes occur in the afternoon and evening hours, with a strong peak showing up during the 5:00 PM hour. Tornadoes are extremely rare in the early morning hours. Solar radiation heats the ground, which heats the lower atmosphere. The atmosphere becomes most unstable during the warmest time of day which is typically in middle to late afternoon. The atmosphere gradually cools and stabilizes after dark, diminishing the threat of severe storms and tornadoes. But tornadoes can occur anytime of day or night. Decade Distribution of Significant Tornadoes
An obvious peak of significant tornadoes occurred in the 1950s, 1960s and 1970s. Although additional data was ingested from SPC starting around 1950, and the local population density was rapidly increasing in the 1950s through 1970s, this doesn't account for the return to pre-1950 trends starting again in the 1980s. Therefore, there is a good deal of certainty that most of the influence on this data is meteorological, a significant finding. Deaths and Injuries from Tornadoes  From this graph, it is evident that 4 tornadoes have been responsible for most of the deaths and injuries in the Chicago area; the Maywood-Melrose Park Tornado of March 28, 1920, the Belvidere and Oak Lawn Tornadoes of April 21, 1967, and the Plainfield Tornado of August 28, 1990.
It’s not surprising that 85% of the deaths and 75% of the injuries have resulted from the most violent tornadoes (F4s and F5s), even though these are rather rare across the Chicago area, accounting for only 16% of the significant tornadoes. If all tornadoes are considered, including weak, non-killer tornadoes, the violent tornadoes would only comprise about 2% of all tornadoes. However, a significant percentage of deaths and injuries were caused by smaller tornadoes (F0-F3). All tornadoes, regardless of size, have the potential to cause deaths and injuries. Multiple Significant Tornado Days When conditions are favorable for the formation of significant tornadoes, sometime several significant tornadoes occur in the same area on the same day. Since 1950, when more reliable record keeping began, there have been nine days that produced multiple significant tornadoes in the Chicago area. The worst was April 21, 1967, when five significant tornadoes occurred, including three violent F4 tornadoes. The most recent event was March 12, 1976 when four significant tornadoes occurred. Before 1950 there were five multiple tornado days documented. There is probably not enough data to draw any conclusions. There have been two in March, four in April, three in May, none in June, one in July, one in August, one in September, none in October, and two in November. County by County Breakdown To look at the frequency of significant tornadoes by county, one must first level the playing field since counties vary greatly in size. Tornado frequency was calculated per hundred square miles. Using this method, Lake County Indiana tops the list with, followed by DuPage and Cook. Will County, popularly thought to be the Chicago area’s “tornado alley” by some, surprisingly only ranks sixth out of the eight counties in the study. Lake County Indiana, along with Cook, also had the most violent (F4 or greater) tornadoes with four. McHenry, Lake Illinois and Will Counties each have had 3 violent tornadoes.
Please note that a tornado’s F scale is assigned based on the maximum damage along its path. If a tornado crossed counties A, B and C, and caused only F0 damage in counties A and C, and F2 damage was confined to a small area in county B, it would be rated an F2 tornado. For this study, the tornado would be counted as a significant tornado for all three counties. Likewise, a tornado that reached F4 or F5 intensity for any part of its path was counted as a violent tornado for all counties in the path of that tornado. Other Significant Tornadoes Near the Chicago Metro Area Here are some notable tornadoes that occurred in north central and northeast Illinois and northwest Indiana, but were outside the eight county Chicago metro area. Rockford - On September 14, 1928 an F4 tornado had a 26 mile path from 8 miles south southwest of Rockford through the southeast side of the city and ended in Boone County. 14 people were killed, 100 injured, and $1.2 million in damage was done. This was part of a large outbreak. There were several other tornadoes in southern Wisconsin. Kankakee - In addition to the 1948 F4 tornado which started in eastern Kankakee County and passed through Lake County Indiana (which is already documented in the Chicago statistics) there was an F4 tornado April 17, 1963. It had a 70 mile path from 3 miles northwest of Essex to just west of Medaryville, IN. It affected Kankakee, Newton, Jasper, and Pulaski Counties. There was near F5 damage with several houses swept away in Kankakee County and again in Jasper County. The worst damage was in the Bradley-Bourbonnais area north of Kankakee. 1 person was killed and 70 were injured. One of the biggest tornadoes of the April 3, 1974 super-outbreak began in rural Benton County, but the most intense damage was at Monticello in White County where the damage path was 1/2 mile wide. This F4 tornado had a 121 mile path but may have been a family of 3 tornadoes. Trends Since 1950
Conclusions
Detailed Information for each of the 86 Tornadoes
Fall is Here, Time to Get the Coats Ready! Meteorological fall is here and that means that temperatures are beginning their gradual decrease into winter. The normal temperature for September through November is 57.1 degrees for Chicago and 50.3 degrees in Rockford. The warmest fall on record was in 1931 for Chicago (60.0 degrees) and Rockford (57.6 degrees). The coldest fall on record was in 1872 in Chicago (48.5 degrees) and in 1976 for Rockford (44.4 degrees). The average first freeze of the season occurs during fall, which is typically on October 15th for Chicago and October 7th for Rockford. With the declining temperatures, it also brings our first chance for snowfall. The average first date of measurable snow is November 16th for Chicago and November 20th for Rockford. The earliest measurable snowfall occurred on October 18th in 1972 and 1989 at Chicago and October 12th in 1909 at Rockford. There has only been one 10”+ snowstorm in Chicago and Rockford’s history during fall. That occurred on November 25th and 26th of 1895 (the Monday and Tuesday before Thanksgiving that year) when 12.0 inches fell in Chicago.
The Return of El Nino On Wednesday, September 13th, the Climate Prediction Center officially announced the return of El Nino conditions in the tropical Pacific and is likely to continue into early 2007. What does this mean for northern Illinois and northwestern Indiana? Well, in terms of temperature, in past El Nino events, the three month period from October through December tends to be warm and January through March tends to be somewhat warm. For precipitation, the three month period from October through December is typically a wet period, while the three month period form January through March tends to be somewhat dry to dry.
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City of Chicago Extreme Weather Notification The National Weather Service has partnered with the City of Chicago to bring advance notice of life threatening weather conditions to residents most at risk. Extreme heat and extreme cold have proved to be killers. More people are killed by excessive heat in the United States than any other weather phenomena. When the National Weather Service issues a Heat Warning or a Wind Chill Warning, the City will activate the Extreme Weather Notification System to provide weather information to those with special needs. Through its Emergency Telephone Notification System (or 911 Callback) the City will contact registered households with a recorded telephone message that will provide (1) weather forecasts and safety tips, (2) City services information (e.g. cooling/warming centers), and (3) how to register for an in-person well-being check. For more information and to sign up for this service, click here.
NOAA Weather Radio in Spanish…A Hopeful Addition With the increasing Spanish speaking population within the Chicago metro area, it has been realized that many individuals may not be able to receive critical weather information. NOAA Weather Radio is a network of radio stations that are programmed to broadcast weather information such as seven day weather forecasts, marine forecasts, and hazardous weather outlooks. In addition, when severe weather threatens, NOAA Weather Radio automatically broadcasts all severe weather products such as severe thunderstorm and tornado watches warnings with an audible alarm. With northern Illinois and northwest Indiana in areas of the U.S. where severe weather is a regular occurrence, NOAA Weather Radio is the first source for these critical warnings. Additionally, NOAA Weather Radio is an “All Hazards” radio network in which critical information such as amber alerts, civil emergency messages, and other potentially life saving information are broadcast. The Romeoville National Weather Service office wishes to create a partnership with local cooperators to pursue a joint venture to provide continuous broadcasts of critical warnings, watches, advisories, and hazardous weather outlooks in Spanish 24 hours a day, as well as seven day weather forecasts, weather synopses, and climate information. Cooperator(s) are being sought to provide tower space, a transmitter, recurring communication and maintenance charges, a generator, and additional equipment and fees necessary to implement a Spanish NOAA Weather Radio transmitter. The National Weather Service will acknowledge the cooperator(s) during the regularly scheduled NOAA Weather Radio broadcasts by recognizing the company or organization at least twice an hour. We at the National Weather Service in Romeoville realize this could be a tremendous asset to the Chicago area. Currently only two locations within the U.S. have NOAA Weather Radio transmitters in Spanish, and Chicago hopes to become the third. All avenues are being pursued in hopes this project will become a reality. If you are interested in helping the National Weather Service secure a NOAA Weather Radio in Spanish, please contact Christopher Gitro at 815-834-1435.
Skywarn Recognition Day December 2, 2006 Skywarn Recognition Day was developed in 1999 by the National Weather Service and the American Radio Relay League. It celebrates the contributions that volunteer Skywarn spotters and amateur radio operators make to the National Weather Service for public safety. Spotters, using radio in the amateur radio frequencies, report severe weather such as flash floods, tornadoes and damaging wind to the National Weather Service Office here in Romeoville. The meteorologists use these reports in preparing warnings for Illinois and Indiana. This year Skywarn Recognition Day will begin at 0000 UTC Saturday December 2, 2006, or 600 PM CDT Friday December 1. It will last 24 hours. Amateur radio operators are invited to the National Weather Service Forecast Office to operate radios and make contacts with other National Weather Service Offices across the United States and other radio operators worldwide. More information will be available on our web page, weather.gov/chicago. Remembering the Wet September of 1986 The fall of 1986 will always be remembered as an unusually wet and unsettled period across much of Illinois and the Great Lakes region. Separate storm systems brought heavy rainfall to much of the Great Lakes. From September 26th through October 6th, very heavy rain fell across northeast Illinois and southeast Wisconsin. Significant flooding and flash flooding resulted within the Des Plaines and Fox River watersheds, with 2200 homes and 150 businesses either damaged or under water. Up to 3300 people were displaced from their homes due to high water. One to two inches of rain per hour fell in the Chicago metro area on the 26th, resulting in the closure of numerous expressways causing rush hour nightmares. The Des Plaines River saw extensive flooding in Lake and Cook counties. Significant flooding also occurred along the upper Fox River. The Des Plaines and upper Fox River basins received between 4 to 10 inches of rain from early August through early September. Soil moisture was high when an additional 9 to 16 inches fell over these same basins from September 10th through September 27th. The additional rainfall resulted in near record to record stages on portions of the Des Plaines and Fox Rivers. The river gage at Gurnee reached a record stage of 11.95 feet, which was 6.95 feet above flood stage. Similarly in Des Plaines, a record stage of 10.88 feet was recorded, which was 5.88 feet above flood stage. Further to the north in Russell, a stage of 10.75 feet was recorded which was 3.75 feet above flood stage. The chart below shows that many locations saw their wettest September on record:
At Chicago O’Hare International Airport, where official climate records are taken for the City of Chicago, 7.12” of rain fell in September making it the 4th wettest on record. Meanwhile, further to the north across portions of Lake County, an amazing 15.91” and 15.11” were recorded at Antioch and Waukegan, making it the wettest September ever recorded at both stations. In all, the 10 day period saw three separate flash flood events across northeast Illinois and southeast Wisconsin. Numerous river gages along the Des Plaines River had record river crests, resulting in $42,000,000 worth of damage. The damage was not restricted to just residential and business establishments, as crop yields were also reduced by as much as 10% due to the persistent heavy rain that fell across Illinois during the late summer and early fall of 1986.
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