The city of 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).
Winters are generally mild, with typical daytime highs between 55 °F (13 °C) and 70 °F (21 °C) and nighttime lows between 35 °F (2 °C) and 50 °F (10 °C). However, strong cold fronts known as "Blue Northers" sometimes pass through Dallas, plummeting nightly lows below 30 °F (−1 °C) for up to a few days and keeping daytime highs in a struggle to surpass 40 °F (4 °C). Snowfall
is usually seen 2–3 days out of the year for an annual average of 2.4
inches, and snow accumulation is typically seen at least once every
winter.[1] 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 the other hand, daytime highs above 65 °F (18 °C)
are not unusual during the winter season. In sum, extremes in 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 United States.
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.[2] Springtime weather can be quite volatile,
but temperatures themselves are mild. The weather in Dallas is also
generally pleasant between late September 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. Over time, tornadoes have perhaps been the biggest natural threat to the city.
The U.S. Department of Agriculture places Dallas in Plant Hardiness Zone 8a.[3] According to the American Lung Association, Dallas has the 12th highest ozone air pollution in the nation, ranking it behind Los Angeles and Houston.[4]
Much of the air pollution in Dallas, and the Metroplex in general,
comes from a hazardous materials incineration plant in the small town
of Midlothian, as well concrete installations in neighboring Ellis County,[5]
but the foremost contributor to air pollution in Dallas is exhaust from
automobiles. Due to the area's spread-out nature and high amount of urban sprawl, automobiles are the only viable mode of transportation for many residents in the metropolitan area.
The city's all-time recorded high temperature is 112 °F (44 °C), while the all-time recorded low is 1 °F (−17 °C). The average daily low in Dallas is 57 °F (14 °C), and the average daily high in Dallas is 77 °F (25 °C).[6] Dallas receives approximately 37.1 inches (942.3 mm) of rain per year.