By Andrew Freedman

Severe thunderstorm season is upon us, with the array of threats it brings, from tornadoes to flash flooding. On Tuesday, tornadoes grabbed most of the headlines, as several strong tornadoes struck the Dallas-Ft. Worth metro area, tossing tracker trailer trucks into the air, and damaging dozens of homes.

But the large hail the same supercell thunderstorms dropped caused major impacts as well, largely because they fell on top of one of the world’s busiest airports.

Enhanced satellite shot of of severe thunderstorms approaching DFW Airport on Tuesday. Click on image for larger version. The blackish marks represent overshooting cloud tops, indicating the strongest thunderstorms with large hail and possible tornadoes. Credit: U.Wisc/CIMSS.

A passenger aboard a flight preparing to depart DFW International Airport when the storm hit described the sounds of the hail hitting their plane to CNN:

“The noise of ice cubes hitting the aluminum exterior of a 757 was as deafening as it was frightening,” he said. “Imagine the sound of dropping a bucket of ice cubes onto a metal-roof shed for about 10 minutes straight.”

Hail and planes don’t exactly get along, and American Airlines, which is based in Dallas, was forced to cancel or delay dozens of flights on Wednesday while about 100 aircraft were inspected for hail damage.

Hail can crack the aluminum skin of an airplane, necessitating costly repairs and keeping planes on the ground instead of in the sky. This is particularly poor timing for American, which filed for Chapter 11 bankruptcy protection in 2011.

Here’s a video of the storm shot by a ramp worker at DFW:

Hail forms as water droplets are rocketed upwards by a thunderstorm’s strong updraft winds, into regions of the cloud that are cold enough for ice to form. Downdrafts can carry hailstones back below the freezing level, where they begin to melt, before adding more layers of ice if other updrafts pick them up. As long as the updrafts can support the balls of ice, they can stay aloft and continue to grow, until they get too heavy, and then, well, thud!

Global warming almost certainly didn’t cause this hail to fall, but it is altering the background conditions in which severe thunderstorms form. There has already been an overall global increase in atmospheric water vapor, which provides more moisture for storm systems to tap into.

The record hailstone that fell in Hawaii on March 9, 2012. Credit: NOAA/NWS.

As I wrote for the Washington Post’s Capital Weather Gang blog last year, as water vapor increases and average temperatures increase, a key severe thunderstorm forecasting metric, known as Convective Available Potential Energy, or “CAPE,” will also increase. A higher CAPE value indicates that there is more potential energy in the atmosphere to fuel thunderstorm development, given something, like a cold front, to set off a storm.

Scientists are working to refine their understanding of how smaller scale weather extremes, like thunderstorms, may respond to an altered climate. Computer models that simulate climate change are only just now becoming advanced enough to simulate such storms, with much research work still to be done.

In the U.S., big hail is typically reserved for the Lower 48 states, where it causes $1 billion in crop damage each year. But recently, Hawaii unexpectedly got in on the act, when rare severe thunderstorms pounded the island, and even spawned a tornado.

This hailstone, which measured 2-inches in diameter, was the largest ever to be recorded in the state. It was twice the size of the old record-holder, which was a comparatively puny 1-inch in diameter.

Original post by ClimateCentral.org.