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NOAA REPORTS FREQUENT TORNADOES NOT THAT UNUSUAL

May 1, 2002 — Three major tornado events in one week aren't exactly old hat for residents of southeastern Missouri, southern Illinois, southwest Indiana and western Kentucky; but it's not a rare occurrence, either, according to statistics kept by NOAA's Storm Prediction Center in Norman, Okla. Residents of the four-state area covered by the NOAA Weather Service office in Paducah, Ky., may have wondered about that frequency in recent days. (Click NOAA photo for larger view of Union County, Ill., tornado damage taken April 28, 2002. Credit "NOAA.")

Storm Prediction Center Director Joseph Schaefer did a preliminary review of the SPC tornado database for an area roughly covering the Paducah Weather Service Office's county warning area to determine whether the frequent tornadoes were a rare occurrence.

Schaefer's review of tornado statistics dating back to 1950 revealed that tornadoes occurred in the area on 208 days in the 1950-2000 time period. On at least half a dozen occasions, tornadoes occurred on three days within a week or less. The 12 tornadoes recorded in the area Dec. 18, 1957, were the most to occur on a single day. There were 10 recorded tornadoes on May 15, 1986; and 11 tornadoes reported on Jan. 21, 1999.

Periods in which three or more tornadoes occurred in a one-week period included May 18, 23, 26, 2000; Jan. 17, 21, 22, 1999; June 10, 12, 14, 1998; April 13, 15, 16, 1998; May 18, 24, 26, 1981; and May 22, 26, June 2, 3, 4, 1973.

The F3 tornado is a much more rare occurrence—both in the four-state area and nationwide, according to Schaefer. Tornadoes of F3 or greater intensity (winds of 158-206 mph) comprise less than seven percent of the tornadoes that occur in the United States. The four-state area involved has experienced only 39 tornadoes of F3 or greater intensity in the period 1950-2000. There have been only 2,780 such tornadoes nationwide in the same period. The USA averages more than 1,000 tornadoes a year.

The worst day for F3 or stronger tornadoes in the four-state area was Dec. 18, 1957, when four were reported. The only other multiple reports came Nov. 13, 1951; May 21, 1957; and Jan. 3, 2000; when two were recorded each day. The only dates on which the area experienced two F3 or greater tornadoes within a week came April 24 and 30, 1970.

Beverly Poole, meteorologist-in-charge at the Paducah Weather Service office, said the recent storms have been caused by a combination of atmospheric conditions common to the spring season.

A strong southwesterly flow of air in the upper atmosphere with a jet stream running at more than 100 mph often stretches from the southern Plains into the middle Mississippi River Valley. Warm, moist and unstable air from the Gulf of Mexico was able to work its way into the region at low levels. Those conditions, Poole said, have been compounded by low-pressure centers moving from the Texas-Oklahoma area into southern Illinois.

"These low-pressure centers lift the air over large parts of the country," Poole said, "The warm fronts and cold fronts associated with these centers act as focusing mechanisms for local severe thunderstorm development. If the winds change direction and speed as they gain altitude through the atmosphere in just the right way, tornadoes can form. We've had these conditions over the lower Ohio River Valley several times over the past week. Each time that has occurred, strong tornadoes have formed."

The recent storms pale in comparison to the Tri-State Tornado of April 1925, which reached maximum intensity of F5 in its 219-mile path of destruction. That tornado killed 695 people and left 2,027 injured. It destroyed 15,000 homes and lasted three hours and 19 minutes.

Relevant Web Sites
Additional information on tornado occurrence may be found on NOAA's Storm Predication Center.

1925 Tri-State Tornado

National Weather Service forecasts for the Quad State Area, along with the latest on the recent tornadoes

NOAA's Storm Watch — Get the latest severe weather information across the USA

NOAA's Tornadoes Page

USA Weather Hazards

NOAA's Weather Page

NOAA's Storm Prediction Center

NOAA's National Severe Storms Laboratory

Media Contact:
Keli Tarp, NOAA's Storm Prediction Center, (405) 366-0451
(Photo courtesy of NOAA's National Weather Service forecast office in Paducah, Ky.)

 

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