WACO, Texas – Tuesday marked the ten-year anniversary of the deadly 2011 Tornado Outbreak which affected a large part of the country.

The outbreak lasted around four days – causing almost $12 billion of damage and leaving more than 300 people dead. The system spawned 362 tornadoes – many of which were large and long-tracking.

The National Weather Service determines the strength of a tornado using the Enhanced Fujita Scale – or EF Scale. The scale starts with wind gusts around 65 mph, which would be an EF-0 tornado, and ends with winds over 200 mph, which would be a deadly EF-5 tornado.

On average, most tornadoes are given an EF-0 or EF-1 rating, but the super outbreak in 2011 spawned three EF-5s, 12 EF-4s, and 21 EF-3 tornadoes. This surpassed the records set by most previous tornado outbreaks.

In Texas alone, there were ten confirmed tornadoes – two of which were EF-2s.

The storms were deadliest in the southeast – where one of the three EF-5 tornadoes developed near Smithville, Mississippi, with wind speeds of 205 mph.

Alabama was hit the hardest by the outbreak. The state accounted for 62 of the recorded tornadoes – the worst of which tracked through the cities of Tuscaloosa and Birmingham, causing 65 deaths and over 1,000 injuries. The clean up in Tuscaloosa alone cost around $100 million.

April 2011 holds the record for most tornadoes in a month. There was a total of 751 tornadoes over the 30 days of April. The previous record was set in May of 2003 – with a little over 500 tornadoes recorded.