Las Vegas has a subtropical hot desert climate , typical of the Mojave Desert in which it lies. This climate is typified by long, extremely hot summers; warm transitional seasons; and short winters with mild days and cool nights. There is abundant sunshine throughout the year, with an average of 310 sunny days and bright sunshine during 86% of all daylight hours. Rainfall is scarce, with an average of 4.2 in (110 mm) dispersed between roughly 26 to 27 total rainy days per year. Las Vegas is among the sunniest, driest, and least humid locations in North America, with exceptionally low dew points and humidity that sometimes remain below 10%.
The summer months of June through September are extremely hot, though moderated by extremely low humidity. July is the hottest month, with an average daytime high of 104.2 °F (40.1 °C). On average, 134 days per year reach or exceed 90 °F (32 °C), of which 74 days reach 100 °F (38 °C) and 7 days reach 110 °F (43 °C). During the peak intensity of summer, overnight lows frequently remain above 80 °F (27 °C), and occasionally above 85 °F (29 °C). While most summer days are consistently hot, dry, and cloudless, the North American Monsoon sporadically interrupts this pattern and brings more cloud cover, thunderstorms, lightning, increased humidity, and brief spells of heavy rain. The window of opportunity for the monsoon to affect Las Vegas usually falls between July and August, although this is inconsistent and varies considerably in its impact from year to year. Summer in Las Vegas is marked by a significant diurnal variation; while less extreme than other parts of the state, nighttime lows in Las Vegas are often 30 °F (16.7 °C) or more lower than daytime highs.
Las Vegas winters are short and generally very mild, with chilly (but rarely cold) daytime temperatures. As in all seasons, sunshine is abundant. December is both the year’s coolest and cloudiest month, with an average daytime high of 56.6 °F (13.7 °C) and sunshine occurring during 78% of its daylight hours. Winter evenings are defined by clear skies and swift drops in temperature after sunset, with overnight minima averaging around 39 °F (3.9 °C) in December and January. Owing to its elevation that ranges from 2,000 to 3,000 feet (610 to 910 m), Las Vegas experiences markedly cooler winters than other areas of the Mojave Desert and the adjacent Sonoran Desert that are closer to sea level. Consequently, the city records freezing temperatures an average of 16 nights per winter. However, it is exceptionally rare for temperatures to reach or fall below 25 °F (−4 °C), or for temperatures to remain below 45 °F (7 °C) for an entire day. Most of the annual precipitation falls during the winter months, but even February, the wettest month, averages only four days of measurable rain. The mountains immediately surrounding the Las Vegas Valley accumulate snow every winter, but significant accumulation within the city is rare, although moderate accumulations do occur every few years. The most recent accumulations occurred on February 18, 2019, when parts of the city received about 1 to 2 inches (2.5 to 5.1 cm) of snow and on February 20 when the city received almost 0.5 inches (1.3 cm). Other recent significant snow accumulations occurred on December 25, 2015, and December 17, 2008. Unofficially, Las Vegas’ largest snowfall on record was the 12 inches (30 cm) that fell in 1909.
The highest temperature officially observed for Las Vegas, as measured at McCarran International Airport, is 117 °F (47 °C), reached June 20, 2017, the last of four occasions. Conversely, the lowest temperature was 8 °F (−13 °C), recorded on two days: January 25, 1937, and January 13, 1963. However, the highest temperature ever measured within the city of Las Vegas was 118 °F (48 °C) on July 26, 1931. The official record hot daily minimum is 95 °F (35 °C) on July 1, 2013, and July 19, 2005, while, conversely, the official record cold daily maximum is 28 °F (−2 °C) on January 8 and 21, 1937.
Due to concerns about climate change in the wake of a 2002 drought, daily water consumption has been reduced from 314 US gallons (1,190 l) per resident in 2003 to around 205 US gallons (780 l) in 2015.