If you are coming to Baton Rouge anywhere from April to October (as well as any other U.S. Gulf coast city), pack at least a few sets of light clothing! The weather here is repetitive during the summer months--hot and humid, with occasional heat index advisories, and occasional scattered thunderstorms, some of which can be strong or severe. Therefore, rain gear is also a necessity.
Outside of the summer, things get a little trickier. High temperatures here have been known to go as high as 85 F (30 C) in the winter, and occasionally never getting out of the 40s. Sometimes strong cold fronts can occur in the winter, and the temperatures can go from the 80s (about 30 C) to the 40s (about 4 C) in just a few hours.
Miscellaneous: To summarize, if you are travelling to Baton Rouge during any season other than the summer, the weather can be very fickle, so be prepared for anything and pack accordingly. (NOTE: It RARELY snows here.)
The city is flat, and if you get a heavy rainstorm the streets, yards, and parks can flood and collect mud . . . so you may not want to bring your most expensive pair of shoes!
Clothing/Shoes/Weather Gear: I arrived November 9th just after a cold front had moved through the southern part of the State. Even coming from the chilly northeast I found the wind to be somewhat uncomfortable although a sweater would have been adequate. This time of year one can go from wearing sundresses or shorts to wearing long pants and sweaters, but a coat isn't really necessary. Summer weather is another story altogether I hear. This is a subtropical zone so keep that in mind. I am told that constant breezes are very common throughout the year due to the proximity of the city to the Gulf. This helps move the humidity and makes the summer heat less intense.