Climate

Dallas has a humid subtropical climate (Köppen climate classification: Cfa) that is characteristic of the Southern Plains of the United States. Dallas experiences distinct four seasons. January is typically the coldest month, with an average low of 37.3 °F (3 °C) and an average high of 56.8 °F (14 °C). Winter is mild but snowfall during winter is not uncommon. On average, there are 2 snowy days per year. Summer is hot and humid. July and August are typically the hottest months, with an average low of 76.7 °F (25 °C) and an average high of 96.0 °F (36 °C). Located at the lower-end of the Tornado Alley, it is often prone to extreme weathers, tornadoes and severe hailstorms.
Winters in Dallas have a normal daily average temperature in January of 47.0 °F (8.3 °C) but sharp swings in temperature as strong cold fronts known as "Blue Northers" pass through the Dallas region, forcing daytime highs below the 50 °F (10 °C) mark for several days at a time and often between days with high temperatures above 80 °F (27 °C). Snow accumulation is seen in the city in about 70% of winter seasons, and snowfall generally occurs 1–2 days out of the year for a seasonal average of 1.5 inches (3.8 cm). Some areas in the region, however, receive more than that, while other areas receive negligible snowfall or none at all.^[38]
A few 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. Temperatures reaching 70 °F (21 °C) on average occur on at least 4 days each winter month. Dallas averages 26 annual nights at or below freezing,^[39] 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,^[specify] the temperature in the region has only twice dropped below 15 °F (−9 °C), though it will generally fall below 20 °F (−7 °C) in most (67%) years.^[39] 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. The lack of any mountainous terrain to the north leaves it open to the sweep of Arctic weather systems.

The Dallas County Courthouse houses the Old Red Museum.

Spring and autumn are transitional seasons with moderate and pleasant weather. Vibrant wildflowers (such as the bluebonnet, Indian paintbrush and other flora) bloom in spring and are planted around the highways throughout Texas.^[40] 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. Autumn often brings more storms and tornado threat, but usually fewer and less severe than in spring.
Each spring, cold fronts moving south from the North 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.^[41][42] 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.^[43] 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.^[44]
The all-time record low temperature within the city itself is −3 °F (−19 °C), set on January 18, 1930, while the all-time record high is 113 °F (45 °C), set on June 26 and 27, 1980 during the Heat Wave of 1980 at nearby Dallas–Fort Worth Airport.^[39][45] The average daily low in Dallas is 57.4 °F (14.1 °C) and the average daily high is 76.9 °F (24.9 °C). Dallas receives approximately 37.6 inches (955 mm) of rain per year.