Things usually cool down after dark, but shortly after midnight on 24 June the temperature rose rapidly from 30C (86F) to 37C (99F) in the Texas town of Breckenridge. This made it briefly the hottest place in the Western hemisphere, thanks to an effect known as a heat burst.
On hot summer days, rising warm air often produces enormous anvil-shaped clouds. These clouds may release an evening shower of rain into dry air below. The rain evaporates, cooling the air suddenly so it starts to sink. The mass of falling air heats up as the pressure increases, but momentum keeps it going down until it reaches the ground and fans outwards. Witnesses experience a blast of hot dry air like a hairdryer – in Breckenridge 47mph (75kph) gusts were recorded.
Heat bursts are comparatively rare, with June being the month when they are most likely. Microburst storms, in which the downward-moving mass of air is accompanied intense rain or hail, are more common, but lack the heating effect.
More powerful heat bursts than Breckenridge have been recorded. Buildings were damaged in 70mph winds from a 2004 Nebraska heat burst, but tales of a 1960 Texas event in which growing cotton was scorched and corn roasted on the stalk are probably exaggerated.
