Summer = HOT! I’m talking 90+ degrees Fahrenheit with high humidity. It's like swimming on dry land! It’s not bad for just walking around, but you can work up a sweat even doing that. If you actually want to do some sort of intense activity, it’s best to do it early in the morning or late in the afternoon. Since your sweat won’t really cool you off, you’ll have to be especially careful of heatstroke and drink a lot of water. Having AC is a must. New Orleans summers are part of the reason locals are stereotyped as lazy; they’re not lazy, it’s just too damn hot!
Winter = Varies. This year we gave Winter a miss and went straight from Fall to Spring. When we do have winter, it definitely gets cold enough to need a jacket or maybe two, but you won’t need thermal underwear. Some people say the humidity makes the cold harder to escape from, but I think that’s one you’d have to decide for yourself. Snow is a rare event, and in my opinion, mercifully so. Driving in New Orleans isn’t the best experience to begin with, but when it snows, drivers freak out. Considering the number of bridges we have, that whole “bridge may ice before road” thing can become particularly troublesome. In general, if it looks like there’ll be snow or serious ice, I’d seriously advise staying at home.
Spring/Fall = Meh. Spring is for Mardi Gras and Fall is for Saints football, but not much worth mentioning weather-wise.
Hurricane = Yes, this should count as a season in New Orleans. The start of hurricane season is usually when people refresh their supplies, check the contraflow maps, and pick a place to evacuate to if necessary. Waiting until there’s actually a hurricane in the Gulf to do these things is just a really, really bad idea.