The best months to travel to New Orleans are March, April, October, and November. The air is soft and lush, scented with sweet olive and night-blooming jasmine. The restaurants and bars in the French Quarter and Uptown prop open their doors, and the smell of boiled crawfish and the sounds of jazz spill out onto the streets. These months also mark the height of festival season, including Jazz Fest (April/May), the French Quarter Festival (April), Voodoo Music Experience (October), and the Oak Street Po-Boy Festival (November). While tourism does spike in these months, this city's built to handle far larger crowds (think Mardi Gras and the Sugar Bowl), and the streets rarely feel congested.
The winters, while shorter and milder than in more northerly climes, can bring temperatures to near freezing. The city is often infused with a damp cold and raked with ornery winds. That doesn't stop people from spilling out of their houses for Saints tailgate parties near the Superdome (August through January) or taking to the streets for Mardi Gras (February or March). The two weekends leading up to Fat Tuesday are rife with parades, with the first weekend somewhat more subdued.
Then there's summer, when conditions are hot and damp. And did we mention hot? Like cayenne-pepper hot. Most New Orleanians learn to move slowly and spend their time hunkered in air conditioning awaiting a cool thunderstorm. This is also peak hurricane season (the prime months for truly dangerous storms are August and September), so travelers should have a backup plan in their pocket.