Las Vegas is in the desert, and that can mean hot temperatures. In June, July and August, expect temperatures above 105 F/40 C. May can produce highs of 90+ F/32+ C, as can September. The desert also means great changes in temperature. The mercury can drop nearly 30 F/16 C from daytime highs to nighttime lows, especially in winter. The sudden drops in temperature are often accompanied by windy conditions. And, of course, the desert creates low humidity, bright sun and hardly any rain (annual rainfall averages 4 in/10 cm).
For about two weeks in July or August, there can be slightly higher humidity and thunderstorms. Winters are mild (January temperatures are 33-56 F/1-12 C). If snow falls at all, it usually melts soon after it touches the ground.