National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

Over the span of about four hours from late on April 19 into the early morning hours of April 20, 2011, a squall line brought a historic number of tornadoes to southern Indiana and central Kentucky.  Storm surveys over the subsequent few days uncovered 24 tornadoes -- the most ever recorded here in one outbreak (there were 21 tornadoes here during the Super Outbreak April 3, 1974).

On the 19th, a low pressure system had organized over southeast Kansas with a stationary front reaching east into the central Appalachians.  Plentiful moisture streamed northward from the Gulf of Mexico ahead of the system.  The Kansas low moved along the front and swung a cold front eastward.  Instability, strong upper level winds, and significant changes in wind speed and direction with height helped cause a large squall line to develop ahead of the low and its cold front.  The squall line caused severe weather from the eastern Great Lakes to the Red River Valley.  Two dozen tornadoes spun up along the line as it crossed southern Indiana and central Kentucky.  Despite the numerous twisters and the fact that they struck during the overnight hours, thankfully, there were no fatalities or injuries.

Storm Prediction Center's 19-20 April 2011 Event Page

	Click on the image to the left to view a 4-panel radar loop of ground velocity from Evansville's radar KVWX (upper-left), storm-relative velocity from KVWX (upper-right), ground velocity from Louisville's radar KLVX (lower-left), and storm-relative velocity from KLVX (lower-right).  The loop shows the squall line entering Dubois County, IN, the most northwestern portion of our County Warning Area.  Five tornadoes occurred in Dubois County alone, formed from circulations along the leading edge of the squall line (brighter colors indicate higher velocity values; i.e., the tornado-causing circulations).  Click on Dubois County on the map at the bottom of the page to view the individual tornadoes.
Click on the two images above to view a 4-panel radar loop of the lowest 4 levels of reflectivity from KLVX (left) and the lowest 4 levels of ground velocity from KLVX (right).  The reflectivity loop shows the hook echo associated with the Breckinridge County/Meade County tornado.  The ground velocity loop shows high velocities (dark blue coloring) associated with that tornado (roughly 80 knots, or over 90 mph!).

Click on a highlighted county in the map below, or in the table beneath the map, to learn about that county's tornadoes and to see pictures of the damage.

 This event has been featured at the National Weather Association's 36th Annual Meeting: