The near-record water levels in the Mississippi River in Louisiana that forced the Army Corps of Engineers to open the Morganza Floodway for only the second time, flooding much of the Atchafalaya River basin, was the biggest weather story of the year in the state, according to state climatologist Barry Keim.
While the high river didn't bring catastrophic flooding to the state, it packed a punch to the state's economy. "The whole industrial corridor from Baton Rouge to New Orleans was severely impacted by that, as well as navigation on the river," Keim said. "The implications were much larger than just the flood."
The corps began monitoring levees throughout the state in mid-March, as a combination of melting snow and heavy rainstorms in the Midwest swelled the Mississippi.
On May 9, the corps ordered the opening of the Bonnet Carre Spillway, just upriver of New Orleans, to divert a portion of the water into Lake Pontchartrain, as the river threatened to flow at a rate of 1.25 million cubic feet per second past New Orleans.
At its peak, 330 of the spillway's 350 bays were opened.
At its highest point, the river reached 17 feet high at the Carrollton Gage in New Orleans, which is the official flood stage, although floodwalls protect the city to 20 feet.
At the river's peak, 17 of Morganza's 125 bays were opened, allowing 182,000 cubic feet of water per second to flow into the Atchafalaya basin, eventually making its way past Morgan City. There, the water inundated all businesses that operated outside the city's floodwalls.
In the Atchafalaya basin, the water caused minor flooding of low-lying populated areas.
The last bays of the Bonnet Carre Spillway were closed on June 20, while the final bay at the Morganza structure wasn't shut until July 7.
Louisiana's second-biggest weather story in 2011 was a lack of rainfall that caused federal climatologists to declare much of the state to be in "extreme drought" for much of the year.
"The U.S. Drought Monitor comes out with a map once a week, and I've flipped through all 52 weeks, and there was drought somewhere in the state every single week of the year," Keim said. "It reached its peak on June 21st, when 65 percent of the state was in 'exceptional drought,' which is the worst classification."
Drought conditions are expected to continue this winter and spring, thanks to conditions that are expected to be warmer and drier than normal, Keim said. The problem is La Nina, a climate pattern caused by colder-than-normal surface water temperatures in the eastern Pacific Ocean, he said.
With the state's record drought conditions, it's no surprise that the year's third-biggest weather story was unexpectedly warm temperatures.
Louisiana had the hottest summer on record, with temperatures averaging 85 degrees, nearly 4 degrees above the long-term average, based on records going back to 1895. 2011 was the fourth-hottest summer on record for any state in the nation, with Texas and Oklahoma setting records this year for the top two spots, Keim said.
Nationwide, it was the second-warmest summer on record, according to the National Climatic Data Center.
The hottest place in the state was Shreveport, which recorded 62 days with temperatures over 100 degrees, extending into the fall and overwhelming the previous record of 47 days with 100-plus temperatures.
The only real break in the state's hot, dry year came with the state's fourth-biggest weather story of 2011, Tropical Storm Lee. The early September storm, actually declared a subtropical cyclone as it came ashore over New Orleans on Sept. 3, dropped between 10 inches and 15 inches on the state, Keim said.
"It was probably more of a benefit than a problem, bringing drought relief to a state that's been parched," Keim said. "And this marks the sixth straight year without a major hurricane landfall in the U.S."
He said there have been two stretches of five years with no major hurricanes, which are Category 3 or larger storms with sustained winds of 111 mph or greater, but this has been the only six-year period without a larger hurricane since record-keeping began.
The fifth-biggest weather story this year was the April 25-27 north Louisiana tornado outbreak, Keim said. In two days, meteorologists monitored 20 tornadoes, including five with winds of 86 mph to 110 mph, and two with winds of 111 mph to 135 mph.
The worst of them hit the cities of Zwolle, near the Texas border in Sabine Parish, and Natchitoches, in the parish of the same name, between midnight and 1 a.m. on April 27. The Zwolle tornado packed winds of 110 to 120 mph, and scored a 17-mile path, destroying several homes, but causing no deaths.
The Natchitoches tornado traveled 26 miles, crossing both the Cane and Red rivers, and also had winds of 110 to 120 mph. This storm, however, was also accompanied by an unusual 2-mile-wide downburst of 110-mph winds between the towns of Point Place and Bermuda. Again, there were no deaths, and scattered damage to homes.
"Part of the same tornado outbreak spilled over into Mississippi on the 26th and 27th, and ultimately led up to the Tuscaloosa tornado," he said, a twister that killed 240 people in Alabama on April 27.
The National Weather Service lists the four-day outbreak as the fourth-deadliest in U.S. history.
The beginning of the new year looks like a continuation of dry, warm conditions, Keim said.
"We've been in drought all year long, and since we're still in a La Nina, and they tend to bring warm and dry conditions, especially in winter and spring. We're already starting out the year behind, and the long-range forecasts do not look good as we get into the next growing season," he said.
That's bad news for farmers and the cattle industry, he said.
And if La Nina extends into the summer, it could mean another active hurricane season, he said.
The La Nina weather pattern results in less wind shear in areas of the Atlantic Ocean where hurricanes form, which means there will be less chance for upper-level winds disrupting their growth.
"The hope is that this thing will fizzle as we get deeper into the spring and we get into a more normal weather pattern, with additional rains, but without the hurricanes," he said.
Mark Schleifstein can be reached at email@example.com or 504.826.3327.