The following is a blog entry from WDRB Meteorologist Jeremy Kappell discussing the Super Outbreak.
The forecast for Wednesday April 3rd, 1974 was for windy and warm conditions with a chance of showers. Needless to say, forecasters got the windy part right!
39 years later, the Super Outbreak of April 3rd 1974 still stands alone as the most widespread and violent tornado outbreak in recorded history.
In terms of total number, path length, and total damage, the massive tornado occurrence of April 3-4, 1974, was more extensive than all previously known outbreaks.
The overall scope of the event has been recently rivaled by the Dixie Alley Outbreak of April 25-28, 2011 only in terms of shear number of tornadoes. However, as Marc points out, the strength of the tornadoes that occurred during the '74 Super Outbreak remains unparalleled.
Although tornado outbreaks are a regular occurrence across the Central and Eastern United States, scientist who have studied this event suggest that one of this magnitude would only occur on the order of once in every several hundred years!
Some of the ingredients that came together for such a massive storm system include extremely strong jet stream winds that were diving out of the Rocky Mountains and into Southern Plains.
Ahead of these vigorous upper level winds, a southerly wind at the surface had pulled up an unseasonably warm and moist (almost tropical) airmass into the lower levels of the atmosphere.
In between these fast paced upper level jet stream winds and the low level "tropical" airmass was a dry layer of air that had been pulled over the region from the Desert Southwest.
This dry layer of air acted as a "lid" and initially suppressed the development of clouds and showers. This lid, also known as a "cap", allowed energy to build at the surface with daytime heating and an increasingly moist flow out of the south.
Finally, the energy in the low levels became too much and the cap broke with a sudden release of energy in the form of explosive thunderstorms during the afternoon hours on April 3rd.
Infrared Satellite Image from 5 pm ET showing the scope of the storm system. The southwest to northeast oriented bright white plumes are lines of tornadic thunderstorms stretching from the Lower Great Lakes through the Ohio and Tennessee Valleys and into the South.
As these storms thrusted through the atmosphere, they were quickly invigorated by the force of the upper level winds causing them to rapidly rotate.
Just about every storm that went up went on to produce a tornado!
In total, the event spawned a staggering 148 confirmed tornadoes that impacted 13 states across the Eastern US from New York and Michigan all the way down into parts of Alabama and Mississippi. One twister even crossed into Windsor Canada!
This map was produced by Dr. Theodore Fujita (Creator of the F-Scale for Tornadoes) from the University of Chicago showing individual tracks of all 148 tornadoes. They are numbered in chronological order.
It wasn't just the shear number of tornadoes that made this outbreak stand out as one of a kind. It was the strength and longevity of these storms. In total, 64 storms reached at least F-3 in intensity with 23 F-4's and unbelievably six achieved F-5 status!
To put this into perspective, the United States on average sees less than one F-5 (EF-5) each year, and on this day there were SIX of them!!!
Many of these monsters had very long tracks too. 21 tornadoes produced continuous tracks of at least 30 miles and three had tracks that covered more than 100 miles! You can see a complete list of the April 3, 1974 tornadoes here.
While the outbreak affected a huge chunk of real estate that covered much of the East-Central United States, Kentuckiana was caught in the middle of it.
In total, 37 tornadoes struck Indiana and Kentucky that day including the Louisville F-4 that touched down on the south part of the city and ripped through the East End.
There were also two F-5's that occurred in the viewing area that afternoon.
The storm pictured here near Depauw Indiana in Harrison County was very unusual in that it had no apparent visible funnel for portions of it's track, yet it was a mile wide at times and was at F-5 intensity at the time this photo was taken.
This storm went on to destroy both my parent's and grandparent's homes in Palmyra Indiana.
After briefly lifting, the storm reformed as it quickly traveled northeast leveling parts of Hanover and Madison Indiana.
Brandenburg was hit harder than anyone as the town of 3,000 was completely leveled by an F-5. The extremely violent storm killed 31 people while sweeping much of the town into the Ohio River.
When all was said and done, 315 people lost their lives that day and another 5,000 were injured by the unprecedented outbreak. Hopefully, we don't have to see anything like this again anytime soon.
Here are some more iconic images from that fateful day...
Interested in learning more about the '74 Super Outbreak?
Here are some of my favorite links on the subject...
The date was April 3, 1974, and the time was 2:55 p.m. Henry W. Armstrong recalls what happened on what is now known as Black Wednesday.More >>