The deadliest storms of the year hit the South yesterday (April 4).
The latest storm report totals — all of the day's severe weather events — from yesterday are up to 1,112, according to the nation's Storm Prediction Center in Norman, Okla. The storm probably wasn't quite that active, one forecaster said, and produced fewer tornadoes than might be expected for such a massive, deadly storm.
At least six people were killed across the South, according to local news reports. None of the deaths were pinned on any of the 20 reported tornadoes, and only two tornado-related fatalities have been reported so far this year. [Infographic: Tornado! An Inside Look at Tornado Season]
Nearly all of the storm reports were for hail larger than golf balls or wind speeds faster than cars on a highway.
That's because the "basic mode of convection was a line of storms, rather than isolated storms," said Harold Brooks, an atmospheric scientist at the National Severe Storms Laboratory in Norman. "Lines tend to produce winds."
Yesterday's tornado count was not that impressive for such an active storm system. It was only the third biggest tornado outbreak this year. On March 9 and Feb. 24, 25 tornadoes were reported in Dixie Alley. Last year's busiest tornado day, June 17, saw 115 reported tornadoes.
Tornadoes usually form when the wind at the Earth's surface is blowing in a different direction — usually from the east or southeast — than wind at 10,000 or 20,000 feet (3,000 to 6,000 meters) above the ground, which is usually blowing in a westerly directions, said Grady Dixon, a climatologist and meteorologist at Mississippi State University.
"This helps promote shear and increases the likelihood of rotating tubes of air that can be ingested into thunderstorms," Dixon told OurAmazingPlanet.
But the setup yesterday didn't feature much of this change in wind direction.
"Yesterday's event saw mostly wind from the southwest at all levels because the surface low pressure was well to the north, in Canada," Dixon said.
On the surface, the number of storm events reported from yesterday is nearly triple last year's busiest day, and would be the most active day since at least 2000. But storm reports aren't being filtered anymore. In the past, a report that was nearby or within minutes of another report was considered a duplicate report. The reports are more inclusive now.
"This has made the number of reports seem very, very large," Brooks said.
Last year's most active weather days were June 18 and Oct. 26, with 403 reports each. The previous most-active day of the last decade was April 2, 2006, with 1,012 storm reports.
April 4 happens to be a history-laden day for tornadoes — on the same date nearly 40 years ago, the infamous Super Outbreak devastated the Midwest and South.
On April 3 and 4, 1974, 148 tornadoes swept across 13 states during the largest outbreak of tornadoes in U.S. history. The killer tornadoes claimed 330 lives.
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.