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More Storms Threaten On 'Super Outbreak' Tornado Anniversary
This storm system spun off 148 tornadoes across 13 states on April 3 and 4 in 1974.
Credit: NOAA.

People are hunkering down today for what could be the worst severe weather of the year — and it just happens to come on the same day in history as the largest tornado outbreak of all time.

On April 3 and 4, 1974, 148 tornadoes swept across 13 Midwestern and Southern states during the largest outbreak of tornadoes in U.S. history. The killer tornadoes  — together called the Super Outbreak — claimed 330 lives.

A satellite image from 1974 shows the outbreak in progress. Three squall lines — severe thunderstorms that form along or ahead of a cold front — roared east at 5 p.m. EDT (2100 GMT) on April 3. [Infographic: Tornado! An Inside Look at Tornado Season]

The storm system spawned six tornadoes of the highest classification — an F-5 on the Fujita scale (since replaced by the Enhanced Fujita Scale) — an unprecedented number from a single storm event. The Super Outbreak was the result of warm, moist air shooting north from the Gulf of Mexico and hitting a whopper mass of cold, dry air moving east from the Rocky Mountains.

Tornadoes are nearly impossible to forecast in advance. But meteorologists can predict the conditions that are ripe for tornadoes to potentially form.

Similar conditions have developed today and widespread severe thunderstorms are expected over parts of the lower Mississippi Valley into the Tennessee Valley today and tonight, according to the Storm Prediction Center in Norman, Okla.

Only one tornado has been reported so far today, but more than 300 severe weather events have been filed to the Storm Prediction Center since Sunday, mostly consisting of large hail and damaging winds.

A tornado watch has been issued for parts of Arkansas, Tennessee, Kentucky, Mississippi, Indiana and Missouri until 4 p.m. EDT (3 p.m. CDT) today.

Email OurAmazingPlanet staff writer Brett Israel at bisrael@techmedianetwork.com. Follow him on Twitter @btisrael.