A massive thunderstorm front spawned 137 tornadoes, killed at least 180 people, and mangled sections of Tuscaloosa, Birmingham, and Huntsville, Ala., on Wednesday. April is now one of the most violent weather months in the region in decades.

A line of violent thunderstorms - the latest in a deadly series - rolled across the Deep South Wednesday, spawning dozens of tornadoes, razing churches and fire stations, trapping people amid debris, and finally leaving at least 180 people dead, mostly from heavily populated parts of Alabama.

A storm that also took lives in Georgia, Tennessee, Mississippi, Virginia, and Arkansas continued to slide eastward Thursday toward North Carolina. The system became the latest in a series of unusually powerful storm systems that has marched across the US in the past month, leaving April 2011 as one of the most violent weather months in decades.

This particular tornado system is likely to be the deadliest in the US since the April 3-4, 1974, tornado outbreak that killed 318 people from Alabama to Canada. Alabama took the heaviest losses in that event as well, with 77 casualties.

"We had a major catastrophic event here in Alabama with the outbreak of numerous long-track tornadoes," Alabama Gov. Robert Bentley said Thursday morning in a phone briefing with reporters.

Thanks to a lingering La Niña system in the Pacific that has shifted the pattern of wind flows across the US, Tornado Alley - the tornado-manufacturing stretch of the Western plains - has remained relatively quiet while parts of the Midwest, the mid-South, and the Deep South have taken the brunt of atmospheric turmoil.

Storm damage Tuscaloosa Alabama
© Dusty Compton/The Tuscaloosa News/APBystanders look at storm damage along 15th Street in Tuscaloosa, Ala., Wednesday, after a strong tornado moved through the city.
On Saturday, a conglomeration, or family, of tornadoes lit up North Carolina after spawning twisters in at least a dozen other states. More storm systems have moved through this week, leading to tornadoes mixing with wildfires in west Texas, twisters taking aim at Alabama's most populous cities, and storms taking out, in places, the ability of emergency officials to respond to the havoc.

On Tuesday and Wednesday, what some TV meteorologists called a historic line of thunderstorms - weather maps were rife with red - left paths of devastation from Texas to Georgia. Parts of Tuscaloosa, the home of the University of Alabama, were wiped out. The tornado "cut a path of destruction deep into the heart of the city," said Mayor Walter Maddox.

The National Weather Service office near Huntsville was briefly shuttered so employees could take cover in a steel room from an approaching storm. Tornadoes also struck the base of Lookout Mountain, the Tennessee tourist destination, felled the historic "graduation tree" at Berry College in Georgia, and forced the Tennessee Valley Authority to power down three Alabama nuclear plants.

The National Weather Service says it took 137 tornado reports around the South, adding that Alabama saw 66 and Mississippi 38.

Alabama Gov. Robert Bentley mobilized 1,200 National Guard troops to help search and rescue teams that were in places hampered by power outages and large numbers of downed trees.

Governor Bentley pushed back against questions from reporters on Thursday about whether Alabama residents had failed to heed tornado warnings, thus pushing up the casualty toll. "We were very prepared ... but it was just the force of the storms," Bentley said. "When a [large tornado] hits a largely populated area like Tuscaloosa, you cannot move thousands of people in five minutes. When an F4 or F5 tornado hits, there's not much you can do to change the outcome of that."

President Obama declared Alabama a federal disaster area Wednesday.

"Our hearts go out to all those who have been affected by this devastation, and we commend the heroic efforts of those who have been working tirelessly to respond to this disaster," Mr. Obama said in a statement.