Texas's great size and topographic variety make climatic description difficult. Brownsville, at the mouth of the Rio Grande, has had no measurable snowfall during all the years that records have been kept, but Vega, in the panhandle, averages 23 in (58 cm) of snowfall per year. Near the Louisiana border, rainfall exceeds 56 in (142 cm) annually, while in parts of extreme West Texas, rainfall averages less than 8 in (20 cm). Average annual precipitation in Dallas (1971–2000) was 34.7 in (88 cm); in El Paso, 9.4 in (23.9 cm); and in Houston, 47.8 in (121.4 cm).

Generally, a maritime climate prevails along the Gulf coast, with continental conditions inland; the Balcones Escarpment is the main dividing line between the two zones, but they are not completely isolated from each other's influence. Texas has two basic seasons—a hot summer that may last from April through October, and a winter that starts in November and usually lasts until March. When summer ends, the state is too dry for autumn foliage, except in East Texas. Temperatures in El Paso, in the southwest, range from a mean January minimum of 29°F (–2°C) to a mean July maximum of 96°F (36°C); at Amarillo, in the panhandle, from 23°F (–5°C) in January to 91°F (33°C) in July; and at Galveston, on the Gulf, from 48°F (9°C) in January to 88°F (31°C) in August. Perhaps the most startling contrast is in relative humidity, averaging 34% at noon in El Paso, 44% in Amarillo, and 72% in Galveston. In the Texas panhandle, the average date of the first freeze is 1 November; in the lower Rio Grande Valley, 16 December. The last freeze arrives in the panhandle on 15 April, and in the lower Rio Grande Valley on 30 January. The valley thus falls only six weeks short of having a 12-month growing season while the panhandle approximates the growing season of the upper Midwest.

Record temperatures range from –23°F (–31v) at Seminole, on 8 February 1933, to 120°F (49v) at Seymour in north-central Texas on 12 August 1936. The greatest annual rainfall was 109 in (277 cm), measured in 1873 at Clarksville, just below the Red River in northeast Texas; the least annual rainfall, 1.786 in (4.47 cm), was recorded at Wink, near the New Mexico line, in 1956. Thrall, in central Texas, received 38.2 in (97 cm) of rain in 24 hours on 9–10 September 1921. Alvin, in Brazoria County on the Gulf Coast, had 43 in (109 cm) of rain on 25–26 July 1979, a national record for the most rainfall during a 24-hour period. Romero, on the New Mexico border, received a record 65 in (165 cm) of snow in the winter of 1923–24, and Hale Center, near Lubbock, measured 33 in (84 cm) during one storm in February 1956. The highest sustained wind velocity in Texas history, 145 mph (233 km/hr), occurred when Hurricane Carla hit Matagorda and Port Lavaca along the Gulf coast on 11 September 1961.

Hurricanes strike the Gulf coast about once every decade, usually in September or October. A hurricane on 19–20 August 1886 leveled the port of Indianola; the town (near present-day Port Lavaca) was never rebuilt. Galveston was the site of the most destructive storm in US history: on 8–9 September 1900, a hurricane blew across the island of 38,000 residents, leaving at least 6,000 dead (the exact total has never been ascertained) and leveling most of the city. A storm of equal intensity hit Galveston in mid-August 1915, but this time, the city was prepared; its new seawall held the toll to 275 deaths and $50 million worth of property damage. Because of well-planned damage-prevention and evacuation procedures, Hurricane Carla—at least as powerful as any previous hurricane—claimed no more than 34 lives. More recent hurricanes have frequently passed over the coastal area with no loss of life at all. Texas also lies in the path of "Tornado Alley," stretching across the Great Plains to Canada. The worst tornado in recent decades struck downtown Waco on 11 May 1953, killing 114 persons, injuring another 597, and destroying or damaging some 1,050 homes and 685 buildings. At least 115 tornadoes—the greatest concentration on record—occurred with Hurricane Beulah during 19–23 September 1967; the 67 tornadoes on 20 September set a record for the largest number of tornadoes on one day in the state.

Floods and droughts have also taken their toll in Texas. The worst flood occurred on 26–28 June 1954, when Hurricane Alice moved inland up the Rio Grande for several hundred miles, dropping 27 in (69 cm) of rain on Pandale above Del Rio. The Rio Grande rose 50 to 60 ft (15–18 m) within 48 hours, as a wall

of water 86 ft (26 m) high in the Pecos River canyon fed it from the north. A Pecos River bridge built with a 50-ft (15-m) clearance was washed out, as was the international bridge linking Laredo with Mexico. Periodic droughts afflicted Texas in the 1930s and 1950s.