It’s that time of year again when flowers bloom, ice starts to find its way into coffee and afternoon strolls are a must. Ah, spring. Yet for all the wonders warmer temperatures can bring, there are a few downsides. Allergies for one. But those are just a minor nuisance compared to severe weather and the tornadoes it can spawn that generallyMore
After spring storms tore through the Dallas-Forth Worth area on Monday evening, social media lit up with photos of chunks of hail the size of golf balls, tennis balls and even softballs and the damage they caused to windows, roofs and cars.
— Samantha Davies (@SDaviesNBC5) April 12, 2016
Such sizable hail — the largest of which was reported at 4.25 inches in diameter — isn’t unusual in this region, which is part of what you might call “Hail Alley.” But climate scientists say the warming of the planet driven by the accumulation of greenhouse gases in the atmosphere could mean large hail falls from the sky more frequently, putting more roofs and car windshields in Dallas and elsewhere at risk.
Hail is a costly part of severe weather, more so than often more-publicized tornadoes, because it happens over a bigger area and is longer lasting.
“And it happens every single year,” John Allen, a climate scientist at Columbia University who studies how climate change might impact severe weather, said.
Hail forms in severe thunderstorms that have strong updrafts, or air that moves rapidly upwards. Rain caught in an updraft is pushed high into the storm cloud, eventually moving above the freezing level where it becomes supercooled and condenses onto dust or other particles and then freezes. While updrafts work to keep the ice aloft, gravity works to pull it downward.
— Eric Jeansonne KFDX (@Weatheric) April 12, 2016
This tug of war moves the ice up and down through the freezing level where it collides with other ice and raindrops that freeze onto it.
Eventually, the hailstone becomes too hefty for the updrafts to keep it aloft and it plummets to the ground. The bigger the hail, the stronger the updraft needed to keep it from falling.
Strong updrafts require a more unstable atmosphere, which is linked to the amount of water vapor the air contains. One of the most well-established consequences of atmospheric warming is the capacity for the air to hold more water vapor, which means that the instability that drives severe storms is expected to increase in the future.
That would seem to be a boon for hail, but it’s not the whole story.
— Dan Peck (@danpeckwx) April 12, 2016
The heating of the atmosphere also means that the freezing level is expected to rise, Allen said, which means hailstones have a deeper pocket of warm air to fall through before reaching the ground. Studies have suggested this could mean that smaller hail — below about 2 inches in diameter — will fall less often in the future because they are more likely to melt.
Larger hail, like that that smashed through windows in Dallas, though, is better able to survive because it takes much more heat to melt it. So with a higher freezing level affecting it less — but increased instability giving it a boost — large hail is expected to happen more often, Allen said.
There are other factors that affect hail formation, Allen said, and research into how warming might impact severe weather is still in its infancy.
But because of the damage to property that hail can cause — it is expected to be in the hundreds of millions in the Dallas area from this event, said Steve Bowen, an associate director and meteorologist with the reinsurance group Aon Benfield — this could be an important concern.