Dallas has a humid subtropical climate, though it is located in a region that also tends to receive warm, dry winds from the north and west in the summer, bringing temperatures well over 100 °F (38 °C) at times and heat-humidity indexes soaring to as high as 117 °F (47 °C). When only temperature itself is accounted for, the north central Texas region where Dallas is located is one of the hottest in the United States during the summer months, usually trailing only the Mojave Desert basin of Arizona, southern Nevada, and southeastern California.
Winters in Dallas are generally mild, with normal daytime highs ranging from 55 °F (13 °C) to 70 °F (21 °C) and normal nighttime lows falling in between 30 °F (?1 °C) and 45 °F (7 °C). A day with clear, sunny skies, a high of 63 °F (17 °C), and a low of 36 °F (2 °C) would thus be a very typical one during the winter. However, strong cold fronts known as "Blue Northers" sometimes pass through the Dallas region, plummeting nightly lows below 30 °F (?1 °C) for up to a few days at a time and keeping daytime highs in a struggle to surpass 40 °F (4 °C). Snow accumulation is usually seen in the city at least once every winter, and snowfall generally occurs 2-3 days out of the year for an annual average of 2.5 inches. Some areas in the region, however, receive more than that, while other areas receive negligible snowfall or none at all.A couple of times each winter in Dallas, warm and humid air from the south will override cold, dry air, resulting in freezing rain or ice and causing disruptions in the city if the roads and highways become slick. On the other hand, daytime highs above 70 °F (21 °C) are not unusual during the winter season and will occur at least several days each winter month-roughly the same number of days each December, January, and February that low temperatures fall below 30 °F (?1 °C) or that high temperatures fail to reach 50 °F (10 °C). Over the past 15 years, Dallas has averaged 31 annual nights at or below freezing, with the winter of 1999-2000 holding the all-time record as having the fewest freezing nights, with 14. During this same span of 15 years, the temperature in the region has only twice dropped below 15 °F (?9 °C), though it will generally fall below 20 °F (?7 °C) about once every other year.In sum, extremes and variations in winter weather are more readily seen in Dallas and Texas as a whole than along the Pacific and Atlantic coasts, due to the state's location in the interior of the North American continent and the lack of any mountainous terrain to the north to block out Arctic weather systems.
Spring and autumn bring pleasant weather to the area. Vibrant wildflowers (such as the bluebonnet, Indian paintbrush and other flora) bloom in spring and are planted around the highways throughout Texas.Springtime weather can be quite volatile, but temperatures themselves are mild. The weather in Dallas is also generally pleasant from late September to early December and on many winter days, but unlike in the springtime, major storms rarely form in the area.

Each spring, cool fronts moving south from Canada will collide with warm, humid air streaming in from the Gulf Coast, leading to severe thunderstorms with lightning, torrents of rain, hail, and occasionally, tornadoes. Over time, tornadoes have probably been the biggest natural threat to the city, as it is located near the heart of Tornado Alley.
The U.S. Department of Agriculture places Dallas in Plant Hardiness Zone 8a.However, mild winter temperatures in the past 15 to 20 years have encouraged the horticulture of some cold-sensitive plants such as Washingtonia filifera and Washingtonia robusta palms. According to the American Lung Association, Dallas has the 12th highest air pollution among U.S. cities, ranking it behind Los Angeles and Houston.Much of the air pollution in Dallas and the surrounding area comes from a hazardous materials incineration plant in the small town of Midlothian and from concrete installations in neighbouring Ellis County.Another major contributor to air pollution in Dallas is exhaust from automobiles. Due to the metropolitan area's spread-out nature and high amount of urban sprawl, automobiles are the only viable mode of transportation for many.
The city's all-time recorded high temperature is 113 °F (45 °C), while the all-time recorded low is ?8 °F (?22 °C). The average daily low in Dallas is 55.0 °F (12.8 °C), and the average daily high in Dallas is 76.3 °F (24.6 °C).Dallas receives approximately 33.3 inches (845.8 mm) of rain per year.