Dallas has a humid subtropical climate, yet this part of Texas also tends to receive warm, dry winds from the north and west in the summer. Winters are generally mild, although strong cold fronts from the north sometimes pass through Dallas, occasionally plummeting nightly lows between 10 °F (−12 °C) and 20 °F (−7 °C). Snowfall is seen on average 5 days out of the year and snow accumulation is seen 3 days out of the year. Occasionally, warm and humid air from the south overrides cold, dry air, leading to freezing rain, which usually causes major disruptions in the city if the roads and highways become dangerously slick.

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 generally mild. The weather in Dallas is also pleasant between late September and early November, and unlike springtime, major storms rarely form in the area.

In the spring, cool fronts moving from Canada collide with warm, humid air streaming in from the Gulf Coast. When these fronts meet over northern and central Texas, severe thunder storms are generated with spectacular lightning shows, occasional torrents of rain, hail, and at times, a few tornadoes. Over time, tornadoes are perhaps the biggest threat to the city. Dallas was hit by a powerful tornado on 2 April 1957, The tornado would have likely been an F3. On March 28, 2000, the “Fort Worth Tornado” impacted Dallas's neighbor Fort Worth's downtown, and tornado in Arlington, Texas also happened that day damaging some homes. Even though Dallas lies at the lower end of the "Tornado Alley", that day had the worst tornadoes to happen to the metroplex in the last 50 years.

The U.S. Department of Agriculture places the city of Dallas in Plant Hardiness Zone 8a. Dallas has the 12th worst ozone air pollution in the nation according to the American Lung Association, ranking it behind Los Angeles and Houston. Much of the air pollution in Dallas, and the DFW Metroplex in general, comes from a hazardous materials incineration plant in the southern-most suburb of Midlothian, as well as concrete installations in neighboring Ellis County. Another major contributor to air pollution is exhaust from automobiles. Due to Dallas's spread out nature and high amount of urban sprawl, automobiles are the only available mode of transportation for many. All time recorded high is 113F,and all time recorded low is -2F.

The average daily low in Dallas is 57 °F (14 °C) and the average daily high in Dallas is 77 °F (25 °C).[29] Dallas receives approximately 37.1 inches (942.3 mm) of rain per year, much of which is delivered in the spring or summer.