Dallas is located in North Texas, built along the Trinity River. It has a humid subtropical climate (Köppen climate classification: Cfa) that is characteristic of the southern plains of the United States. Dallas experiences mild winters and hot summers.

Summers are very hot and rather humid.Heat waves can be severe and prolonged, usually coinciding with severe drought.The city's all-time recorded high temperature is 113 °F (45 °C) during the Heat Wave of 1980. In July and August, the average high temperature is near 96 °F (36 °C), while the average nighttime low temperature is around 77 °F (25 °C). Days with temperatures exceeding 100 °F (38 °C) happen at least several times during the summer every year. Especially hot and dry summers occurred in 1980, 2011, 2022 and 2023.

Spring and autumn bring warm 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 warm on average. The weather in Dallas is also generally pleasant between late October and early December, and unlike springtime, major storms rarely form in the area.

In the spring, cool fronts moving south from Canada collide with warm, humid air streaming in from the Gulf Coast. When these fronts meet over north central Texas, severe thunderstorms are generated with spectacular lightning shows, torrents of rain, hail, and occasionally, tornadoes (Dallas is located at the lower end of the Tornado Alley).

During the winter months of December to March, daytime highs as high as 76.7–85.9 °F (24.8–29.9 °C) are not unusual during warm spells. On the other hand, a Blue Norther can occur, bringing sudden and possibly-large temperature drops. During cold spells, high temperatures can lower to the 30s F., with low temperatures in the 10-20 F. range, rarely lower than that, for several days. A couple of times each year, warm and humid air from the south overrides cold, dry air, leading to freezing rain, which often causes major disruptions in the city if the roads and highways become slick. On average, even the coldest month of January is generally mild, with an average high of 57.7 °F (14.3 °C) and low of 37.9 °F (3.3 °C). Based on 1991-2020 climate data, the average coldest temperature for an entire year is about 19.1 °F (−7.2 °C), placing Dallas in USDA zone 8b. The all-time recorded low is −3 °F (−19 °C) on January 18, 1930.

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There are two to three days with hail per year, but snowfall is rare. Based on records from 1898 to 2019, the average snowfall is 2.6 inches per year. It has snowed twice during Thanksgiving day NFL football games at Texas Stadium, in 1993 and 2007, which is comparatively early. The month with the highest snowfall is typically February, with an average of 0.6 inches falling. While the month with the highest number of days with snow falling is typically January, with an average of 0.5 days of snow. The record snowfall was recorded in February 2010, when 12.5 inches of snow fell over two days at the Dallas-Fort Worth International airport.

Since Dallas lies at the lower end of the "Tornado Alley", tornadoes have on occasion been a threat to the city. Most tornadoes hit the city during the months of April and May. Dallas was hit by a powerful tornado on April 2, 1957; the tornado was later rated F3. On March 28, 2000, the “Fort Worth Tornado” impacted Dallas's neighbor Fort Worth's downtown, and a tornado in Arlington, Texas also occurred that day damaging some homes. Four people died in Fort Worth as a result of the tornado. That day was the Metroplex's most damaging tornado outbreak since the 1957 event. Another widespread tornado outbreak struck the area in the Dallas tornado outbreak of April 3, 2012, slightly damaging Rangers Ballpark in Arlington and damaging some planes and grounding the others at Dallas/Fort Worth International Airport and Dallas Love Field, heavily damaging an elementary school, and destroying semis in a facility. On December 26, 2015, a rare winter tornado outbreak led to the spawning of several tornadoes, including an EF4 tornado near the city of Garland and Rowlett that caused 10 deaths. On October 21, 2019, 10 tornadoes touched down in the Dallas-Fort Worth Metroplex, including an EF3 tornado that devastated areas from North Dallas to Richardson.