April is the best time to visit Houston. The weather is warm but not yet oppressive, hurricane season has not started, and you avoid the higher prices of the winter tourist season.
Spring (late March to May) brings comfortable temperatures below 77 degrees Fahrenheit with occasional thunderstorms. Summer is brutal: temperatures above 90 degrees with morning humidity around 90%, plus the real risk of hurricanes and tropical storms from the Gulf of Mexico. Autumn stays warm but hurricanes remain possible through October. Winter is mild by most standards, with daytime highs around 60 degrees and only rare freezes, which is exactly why snowbirds flock here from December through March.