Regions of Louisiana

New Orleans is built in a bowl between the river and the lake, and everything about its weather comes down to which way water moves. Half the city sits below sea level, the pumps that empty it can clear about an inch of rain an hour, and a July afternoon routinely beats that. The hurricanes are the ones everyone knows — Betsy in 1965, Katrina in 2005, Ida in 2021 — but the ordinary summer downpour is what floods the streets, and the levee-and-pump system that answers both is the most engineered ground in North America.

Baton Rouge sits at the head of the deep-draft river and on the last high ground the Mississippi touches before the delta, which is why the capital, the refineries and the bridge are all here. It is also one of the wettest large cities in the country at about 63 inches a year, and August 2016 showed what that can do when a stalled low parks over it: two feet of rain in 48 hours with no tropical storm attached, 30 inches at Watson, and flooding in parishes that had never flooded before.

The Northshore is in large part what New Orleans became after Katrina — St. Tammany is among the fastest-growing parishes in the state — and it forecasts differently from the city 24 miles across the lake. Pine flatwoods instead of marsh, a few feet of elevation instead of none, and storms that fire on the lake breeze in the afternoon. I-12 is the bypass: when I-10 through the city closes, everything moving east or west goes across the top of Pontchartrain.

Acadiana is some of the flattest, wettest farmland in the country — rice and crawfish in the same field, the crop rotating with the water — and there is nothing between the Gulf and the prairie to slow anything down. Surge runs up the Vermilion and the Bayou Teche; Rita in 2005 and Laura and Delta in 2020 all came ashore within a hundred miles of here. Lafayette is the Hub City because the highways meet on the last dry ground before the basin.

This is the working coast: the ports that service the offshore rigs, the shrimp and oyster fleet, and the last inhabited ridges of the delta. It is also the fastest-disappearing land in the United States — Terrebonne and Lafourche have lost hundreds of square miles of marsh, and every mile of marsh lost is a mile less of surge protection. The Morganza levee and the Larose-to-Golden-Meadow ring stand in for it now. Ida came ashore at Port Fourchon in 2021 at 150 mph.

Lake Charles took two hurricanes in six weeks in 2020 — Laura on August 27 as a category 4, then Delta on October 9 over the same ground — and followed them with a February ice storm and a twelve-inch rain in May. Cameron Parish below it is the most exposed coast in the state, open marsh with no barrier islands, where Rita's surge reached twenty feet in 2005. The LNG terminals on the ship channel are why the population keeps coming back.

Cenla is where the state stops being coastal. The Kisatchie hills are the first real relief north of the marsh, the pine belt starts here, and winter storms that never reach the Gulf coast do reach Alexandria — ice on I-49 is a Cenla problem, not a New Orleans one. It is also the middle of the state's severe season: the Red River valley is a corridor supercells follow, and the spring line comes through here before it reaches anywhere else.

Shreveport is the far corner of the state and the closest thing Louisiana has to a continental climate: it freezes properly here, the December 2022 arctic outbreak dropped it into single digits, and snow is a real if rare event. It is also the northern end of Dixie Alley — the Shreveport forecast office covers four states — with a severe season that runs from late winter through spring and a second peak in November the coast never sees.

Northeast Louisiana is two landscapes with a river between them. West of the Ouachita it is hill country and pine; east of it the Macon Ridge drops into the Mississippi alluvial plain, flat black delta farmland that floods from the river and from backwater both. The 1927 flood put most of it under, and the levees and the Tensas backwater basin are what came out of that. Monroe and West Monroe face each other across the Ouachita, and the river is the forecast here.