Holy long underwear! A new paper led by Dr. Simon Proud, research fellow at the Department of Physics and the National Center for Earth Observation, reveals the coldest cloud-top temperature in a severe thunderstorm cloud in the Pacific, observed by an Earth-orbiting satellite.

This temperature of -111°C is more than 30°C colder than typical storm clouds and is the coldest known measurement of storm cloud temperature.

In the lowest section of the Earth’s atmosphere, known as the troposphere, air temperature decreases with altitude and can reach as low as -90°C in the tropics. Thunderstorms and tropical cyclones can grow to high altitudes, up to 18km (11mi), and therefore the tops of these storm clouds become extremely cold.

On 29 December 2018, the VIIRS sensor aboard the American NOAA-20 satellite, overflew a severe thunderstorm in the South Western Pacific, approximately 400km South of Nauru. This storm was so powerful that it pushed through the troposphere and into the stratosphere; continuing to cool as it gained height despite the surrounding air being warmer: An event known as an overshooting top. This overshoot led to the storm cloud becoming the coldest known storm cloud temperature recorded, -111°C, and the tops of the clouds reached an altitude of over 20.5km (12.8mi) above sea level.

Dr. Proud explains. “We found that these really cold temperatures seem to be becoming more common—with the same number of extremely cold temperatures in the last three years as in the 13 years before that. This is important, as thunderstorms with colder clouds tend to be more extreme, and more hazardous to people on the ground due to hail, lightning and wind. We now need to understand if this increase is due to our changing climate or whether it is due to a “perfect storm” of weather conditions producing outbreaks of extreme thunderstorms in the last few years.”