The desert climate, in short
Las Vegas sits in the Mojave Desert, which means big temperature swings between seasons and between day and night. Summers are extremely hot and dry; winters are mild by day and can be genuinely cold after dark. Rain is rare year-round, which is part of why the city reads as sunny in almost every photo you've ever seen of it.
Spring and fall: the sweet spot
March through May and October into November are generally considered the most comfortable stretches — warm days, cool evenings, and enough sunshine to make pool time reasonable without the punishing summer heat. These months are also popular, so book hotels and shows ahead if your dates are fixed.
Summer: hot, but not empty
Summer daytime highs regularly climb into territory that makes walking the Strip at midday genuinely uncomfortable. Locals and regulars adapt by shifting outdoor plans to early morning or after dark, and by leaning hard on air-conditioned casino floors, pools and indoor attractions during the afternoon. Hotel rates can dip in the hottest stretches, which is why some visitors treat summer as a value season if they don't mind the heat.
Winter and the shorter days
Winter is mild in the daytime but night temperatures drop enough that an outdoor-only outfit will leave you cold on the Strip after sunset. The holiday period around Christmas and New Year's is one of the busiest and most expensive stretches of the entire year, driven by New Year's Eve crowds on the Strip itself.
Watch the convention calendar, not just the season
Las Vegas is one of the largest convention destinations in the world, and a big trade show in town can push hotel rates up more than any seasonal pattern will. If your travel dates are flexible, checking what's on at the Las Vegas Convention Center before you book can matter more than picking the 'right' month.