Climate of Dallas

T 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. According to the American Lung Association, Dallas has the 12th highest ozone air pollution in the nation, ranking it behind Los Angeles and Houston. 30% of the air pollution in Dallas, and the Metroplex in general, comes from the three cement plants in the town of Midlothian, as well concrete installations in neighboring Ellis County, 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 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 34.7 inches (881 mm) of equivalent rain per year.

The spring and fall seasons are pleasant in Dallas, as seen in this March photograph from an Oak Cliff park

Volatile weather

Tornadoes

A multiple-vortex tornado outside of Dallas, Texas on April 2, 1957.

Since Dallas lies at the lower end of the "Tornado Alley", 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 a tornado in Arlington, Texas also occurred that day damaging some homes. That day was the Metroplex's most damaging tornado outbreak since the 1957 event.

Floods

Major flooding occurred on the Trinity River in the years 1844, 1866, 1871, and 1890, but a major event in the spring of 1908 set in motion the harnessing of the river. On 26 May 1908, the Trinity River reached a depth of 52.6 feet (16.03 m) and a width of 1.5 miles (2.4 km). Five people died, 4,000 were left homeless, and property damages were estimated at $2.5 million.

Now the wreckage of a shed or outhouse would move by, followed by a drowned swine or other livestock. The construction forces of the Texas & Pacific worked feverishly to safeguard the long trestle carrying their tracks across the stream. Suddenly this whole structure turned on its side down-stream, broke loose from the rest of the track at one end and swung out into the middle of the current and began breaking up, first into large sections and then into smaller pieces, rushing madly along to some uncertain destination. [Approximately half a dozen of the workmen fell into the torrent at this point; exaggerated reports of their drowning swept the city.]

— C.L. Moss,

Dallas was without power for three days, all telephone and telegraph service was down, and rail service was canceled. The only way to reach Oak Cliff was by boat. West Dallas was hit harder than any other part of the city—the Dallas Times Herald said "indescribable suffering" plagued the area. Much to the horror of residents, thousands of livestock drowned in the flood and some became lodged in the tops of trees—the stench of their decay hung over the city as the water subsided.

The Trinity River flooding on 8 July 1908.

After the disastrous flood, the city wanted to find a way to control the reckless Trinity and to build a bridge linking Oak Cliff and Dallas. The immediate reaction was citizens and the city clamoring to build an indestructible, all-weather crossing over the Trinity. This had already been tried following the 1890 flood—the result was the "Long Wooden Bridge" that connected Jefferson Boulevard in Oak Cliff and Cadiz in Dallas, but the resulting unstable bridge was easily washed away by the 1908 flood. George B. Dealey, publisher of the Dallas Morning News, proposed a 1.5 miles (2.4 km) concrete bridge based on a bridge crossing the Missouri River in Kansas City. Ultimately a US$650,000 bond election was approved and in 1912, the Oak Cliff viaduct (now the Houston Street viaduct) was opened among festivities drawing 58,000 spectators. The bridge, at the time, was the longest concrete structure in the world.