diurnal tornado frequency

Tornado distribution throughout the year.  Note the increase in tornado activity in the fall and again in mid-winter!  The graph shows the number of days in each month on which at least one tornado has occurred in this area, going back to 1830.

While severe weather in the Ohio and Tennessee Valleys is most common in the spring; deadly storms, including tornadoes, can truly strike at any time of year.  Several cool-season severe weather outbreaks have struck the region over the past several years, including our 3rd  most prolific tornado outbreak on record in early February of 2008.  It is vital to not let our guard down when the weather turns cool.  Our very lives depend on remaining "weather aware" and always being prepared for that next storm.

Click on the links below, or scroll down the page for more information.

How Do Powerful Storm Systems Form? How Does the National Weather Service Detect Severe Storms and Warn the Public?
How Do I Know if a Warning Has Been Issued for My Area? Recent Cool Season Severe Weather Outbreaks
Definitions Links


How Do Powerful Storm Systems Form?

Crawford County lightning

Severe weather often forms in warm, humid air ahead of an approaching cold front or, occasionally, along a warm front.  The warm humid air can become unstable, which means that air currents can rise very quickly and form large storm clouds.  The front helps to provide even more lift to these large bubbles of skyrocketing air.  In cool season severe weather outbreaks there is often a great deal of wind, both at the surface and aloft.  If the winds at the surface are from a different direction or at a different speed from the winds high up in the atmosphere, extreme turbulence can develop and lead to powerful thunderstorms and even tornadoes.

These condtions are able to come together at any time of year, and can result in widespread severe weather despite what the calendar might say.

How Does the National Weather Service Detect Severe Storms and Warn the Public?

radar operator

 Meteorlogists at the National Weather Service (NWS) study for years to be able to interpret data from myriad sources including radar, satellite, computer models, and weather observing networks both on the surface and aloft.  Many people are involved when your local NWS office is working a severe weather event.  Many of these people work in support, either directly or indirectly, of the radar operators.  The radar operators continually watch their screens, looking for any storms that appear to be severe.  NWS Doppler radar is very powerful and scans the atmosphere at many different levels, so that NWS meteorologists can get a complete picture of the entire storm's structure.

If the radar operator feels a Severe Thunderstorm Warning or Tornado Warning is necessary, he uses special software that will locate and provide a forecast track for the storm as well as compose much of the warning.  The meteorologist then makes any necessary edits to the warning that the program generates and sends it out to the public.  The NWS, which is part of the federal government's Department of Commerce, is the nation's only official source of severe weather warnings.

How Do I Know if a Warning Has Been Issued for My Area?

 weather radio

While NWS meteorologists do everything in their power to send out timely and accurate warnings, it is up to you to receive them.  One of the best ways is via NOAA Weather Radio (NWR), which airs all severe weather warnings within seconds of their issuance.  Most NWR's have an alarm that will switch the radio on when a warning is issued, and can be programmed so that they will only go off for certain counties and warnings that you select.  There are also devices for the hearing impaired such as pillow shakers and strobe lights.

Another excellent source of warning information is the main page of our website.  On that page is a map of the forecast area.  When a Tornado Warning is issued, it will show up in red on the map.  When a Severe Thunderstorm Warning is issued, it will light up orange.  You can then click on the map and get all the warning and forecast information pertinent to the spot where you clicked.

Many folks get their warning information from local television or radio media, which are yet another excellent source of information.  On-air meteorologists will often cut into programming to bring you the latest important weather news within moments of issuance by the NWS.


 Recent Cool Season Severe Weather Outbreaks

Hardin County February 29, 2012 February 29, 2012 Leap Day tornadoes
Simpson County EF2 January 17, 2012 January 17, 2012 squall line with tornadoes
February 28 2011 tornado damage February 28, 2011 tornado outbreak
Monroe County February 5-6, 2008 tornado swarm
Central Kentucky
Western Kentucky
Official Assessment
 Washington County, Indiana January 29, 2008 squall line and tornadoes
 Barren County January 10, 2008 hailstorm at Park City, KY
 Clark County, Indiana October 18, 2007 tornadoes
 Adair County January 2, 2006 Elizabethtown and other tornadoes

 Hopkins County
 November 15, 2005 tornadoes
Southern Kentucky
Western Kentucky
 Hart County November 6, 2005 Munfordville tornado
 Evansville tornado  November 6, 2005 Evansville tornado



Warning:  The severe weather described in the warning is either already happening or will happen very soon.  Warnings are issued for parts of counties usually for an hour or less.  Seek sturdy shelter!
Watch:  The severe weather described in the watch may develop over the next several hours.  Watches are issued for parts of states usually for about six hours.
Hazardous Weather Outlook:  This is issued by the NWS in Louisville at least three times a day every day.  It describes all significant weather coming up in the next seven days.  If you have time to look at only one NWS product before you start your day, make it this one.
Severe Thunderstorm:  A thunderstorm producing damaging winds of 58 mph or more, hail at least an inch in diameter, or a tornado.
Tornado:  A violently rotating column of air, almost always associated with a thunderstorm, and in contact with the ground.
Funnel Cloud:  A violently rotating column of air, often associated with a thunderstorm, not in contact with the ground.  Funnel clouds themselves are harmless, but can develop into dangerous tornadoes.
Flash Flood:  A flood that occurs within a few hours of torrential rainfall.  Flash floods are deadly and can develop very quickly.
Downburst:  A powerful gust of wind that descends from a storm cloud and quickly spreads out in all directions when it hits the ground.
Squall line:  A line of strong storms, sometimes hundreds of miles long.
Derecho:  A special kind of squall line that often takes on a bowed backwards "C" shape and is known for intense winds sometimes hitting 100mph.
Supercell:  A large, intense thunderstorm that is usually rotating and is often seperate from other storms.  Supercells are responsible for many instances of severe weather.


Severe Weather Links

Tornado Safety The Enhanced Fujita Scale
Lightning Safety Hail Size and Wind Intensity Descriptors
Flash Flood Safety Local Severe Weather Summary Page
Hazardous Weather Outlook Most Recent Storm Reports
Storm Prediction Center Storm Outlooks Current Severe Weather Watches
Local Storm Outlook Page  NOAA Weather Radio
 Is Your Community StormReady?  SkyWarn
 Local Tornado Catalogue Important Past Weather Events is the U.S. government's official web portal to all federal, state and local government web resources and services.