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Climate

Austin is located within the middle of a unique, narrow transitional zone between the dry deserts of the American Southwest and the lush, green, more humid regions of the American Southeast. Its climate, topography, and vegetation share characteristics of both. Officially, Austin has a humid subtropical climate (Cfa) under the Köppen climate classification. This climate is typified by long, very hot summers, short, mild winters, and warm to hot spring and fall seasons in-between. Austin averages 34.32 inches (872 mm) of annual rainfall distributed mostly evenly throughout the year, though spring and fall are the wettest seasons. Sunshine is common during all seasons, with 2,650 hours, or 60.3% of the possible total, of bright sunshine per year.

Summers in Austin are very hot, with average July and August highs frequently reaching the high-90s (34–36 °C) or above. Highs reach 90 °F (32 °C) on 123 days per year, of which 29 days reach 100 °F (38 °C); all years in the 1991-2020 period recorded at least 1 day of the latter. The average daytime high is 70 °F (21 °C) or warmer between March 1 and November 21, rising to 80 °F (27 °C) or warmer between April 14 and October 24, and reaching 90 °F (32 °C) or warmer between May 30 and September 18. The highest ever recorded temperature was 112 °F (44 °C) occurring on September 5, 2000, and August 28, 2011. An uncommon characteristic of Austin's climate is its highly variable humidity, which fluctuates frequently depending on the shifting patterns of air flow and wind direction. It is common for a lengthy series of warm, dry, low-humidity days to be occasionally interrupted by very warm and humid days, and vice versa. Humidity rises with winds from the east or southeast, when the air drifts inland from the Gulf of Mexico, but decreases significantly with winds from the west or southwest, bringing air flowing from Chihuahuan Desert areas of West Texas or northern Mexico.

Winters in Austin are mild, although occasional short-lived bursts of cold weather known as " Blue Northers " can occur. January is the coolest month with an average daytime high of 62.5 °F (17 °C). The overnight low drops to or below freezing 12 times per year, and sinks below 45 °F (7 °C) during 76 evenings per year, mostly between mid-December and mid-February. The average first and last dates for a freeze are December 1 and February 15, giving Austin an average growing season of 288 days, and the coldest temperature of the year is normally about 24.2 °F (−4 °C) under the 1991-2020 climate normals, putting Austin in USDA zone 9a. Conversely, winter months also produce warm days on a regular basis. On average, 10 days in January reach or exceed 70 °F (21 °C) and 1 day reaches 80 °F (27 °C); during the 1991-2020 period, all Januarys had at least 1 day with a high of 70 °F (21 °C) or more, and most (60%) had at least 1 day with a high of 80 °F (27 °C) or more. The lowest ever recorded temperature in the city was −2 °F (−19 °C) on January 31, 1949. Roughly every two years Austin experiences an ice storm that freezes roads over and cripples travel in the city for 24 to 48 hours. When Austin received 0.04 inches (1 mm) of ice on January 24, 2014, there were 278 vehicular collisions. Similarly, snowfall is rare in Austin. A snow event of 0.9 inches (2 cm) on February 4, 2011, caused more than 300 car crashes. The most recent major snow event occurred February 14–15, 2021, when 6.4 inches (16 cm) of snow fell at Austin's Camp Mabry, the largest two-day snowfall since records began being kept in 1948.

Typical of Central Texas, severe weather in Austin is a threat that can strike during any season. However, it is most common during the spring. According to most classifications, Austin lies within the extreme southern periphery of Tornado Alley, although many sources place Austin outside of Tornado Alley altogether. Consequently, tornadoes strike Austin less frequently than areas farther to the north. However, severe weather and/or supercell thunderstorms can occur multiple times per year, bringing damaging winds, lightning, heavy rain, and occasional flash flooding to the city. The deadliest storm to ever strike city limits was the twin tornadoes storm of May 4, 1922, while the deadliest tornado outbreak to ever strike the metro area was the Central Texas tornado outbreak of May 27, 1997.