Las Vegas has a subtropical hot desert climate (In the Köppen climate classification, that’s abbreviated as BWh), typical of the Mojave Desert in which it is located. This climate is defined by long, sweltering summers; warm times in-between seasons; and short, mild winters at best to chilly ones at worst. There is abundant sunshine throughout the year, with an average of 310 sunny days and bright sunshine during about 90% (rounded off from 86%) of all daylight hours. Rainfall is scarce, with an average of 4.2 in (110 mm) dispersed between about 26 to 27 total rainy days annually. Las Vegas is among the sunniest, driest, and least humid locations in North America, with exceptionally low dew points and humidity that sometimes remains below 10%.
The summer months of June through September are very 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 lower than daytime highs.
Las Vegas winters are short and generally very mild, with chilly (but rarely cold) daytime temperatures. Like 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 lows sinking to 39 °F (3.9 °C) or lower during the majority of nights in December and January. Owing to its elevation that ranges from 2,000 feet to 3,000 feet, 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 fall to or 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 the wettest month (February) averages only four days of measurable rain. The mountains immediately surrounding the Las Vegas Valley accumulate snow every winter, but significant or sustained accumulation within the city is rare. The most recent accumulating snowfall occurred on December 17, 2008, when Las Vegas received 3.6 inches (9.1 cm). Las Vegas’ largest snowfall on record was 12 inches (30 cm) that fell in 1909.
For averages per month, here are the numbers. All metric temperature measurements are in parentheses, while Imperial temperature measurements are not.
In January, average high temperatures are 58.0 (14.4), while average lows are 39.4 (4.1).
In February, average high temperatures are 62.5 (16.9), while average lows are 43.4 (6.3).
In March, average high temperatures are 70.3 (21.3), while average lows are 49.4 (9.7).
In April, average high temperatures are 78.3 (25.7), while average lows are 56.1 (13.4).
In May, average high temperatures are 88.9 (31.6), while average lows are 65.8 (18.8).
In June, average high temperatures are 98.7 (37.1), while average lows are 74.6 (23.7).
In July, average high temperatures are 104.2 (40.1), while average lows are 80.9 (27.2).
In August, average high temperatures are 102.0 (38.9), while average lows are 79.3 (26.3).
In September, average high temperatures are 94.0 (34.4), while average lows are 71.1 (21.7).
In October, average high temperatures are 80.6 (27), while average lows are 58.5 (14.7).
In November, average high temperatures are 66.3 (19.1), while average lows are 46.5 (8.1).
In December, average high temperatures are 56.6 (13.7), while average lows are 38.7 (3.7).
Throughout the year, average high temperatures are 80.1 (26.7), while average lows are 58.7 (14.8).