travel in the city for 24 to 48 hours. When Austin received of ice on January 24, 2014, there were 278 vehicular collisions. Similarly, snowfall is rare in Austin. A snow event of on February 4, 2011, caused more than 300 car crashes. The most recent major snow event occurred February 14–15, 2021, when 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. Natural disasters 2011 drought From October 2010 through September 2011, both major reporting stations in Austin, Camp Mabry and Bergstrom Int'l, had the least rainfall of a water year on record, receiving less than a third of normal precipitation. This was a result of La Niña conditions in the eastern Pacific Ocean where water was significantly cooler than normal. David Brown, a regional official with the National Oceanic and Atmospheric Administration, explained that "these kinds of droughts will have effects that are even more extreme in the future, given a warming and drying regional climate." The drought, coupled with exceedingly high temperatures throughout the summer of 2011, caused many wildfires throughout Texas, including notably the Bastrop County Complex Fire in neighboring Bastrop, Texas. 2018 flooding and water crisis In the fall of 2018, Austin and surrounding areas received heavy rainfall and flash flooding following Hurricane Sergio. The Lower Colorado River Authority opened four floodgates of the Mansfield Dam after Lake Travis was recorded at 146% full at . From October 22 to October 29, 2018, the City of Austin issued a mandatory citywide boil-water advisory after the Highland Lakes, home to the city's main water supply, became overwhelmed by unprecedented amounts of silt, dirt,