It was a mighty hailstorm that hammered Guadalajara Sunday morning, but the amount of reported hail was probably inflated, it wasn’t unprecedented and this wasn’t some new breed of tempest brought about by climate change.
Similar hailstorms have happened before and contributions from climate change, if any, are very uncertain and difficult to discern — at least right now.
To understand what happened in Guadalara, let’s start with the basics. Hail is common in the warm season months and forms in vigorous thunderstorms that have intense zones of rising air, known as updrafts. These updrafts loft a tremendous amount of water vapor high into the sky, where the vapor condenses, freezes into ice and forms hail.
After forming, the hail falls toward the ground, but, if the updrafts are strong enough, the ice is hurled back up into the cloud where more liquid water freezes onto it and the hailstone expands. This process continues until the hail gets so heavy the updraft can no longer lift it, and it crashes to the ground.
Hailstones thus build from the inside out. Cut one in half, and it looks like an onion.
There are different types of hailstorms.
There’s the common pea- to penny-sized barrage that lasts for a few minutes.
In areas more prone to towering, rotating thunderstorms, like the Great Plains, hail may fall over smaller areas, but the stones are much larger, ranging from golf ball to softball size.
Then there is a bizarre type of hail event, sometimes termed a “SPLASH” event — “storms producing large amounts of small hail.”
Aerial views in the aftermath of these SPLASH events often reveal a spectacular, bone-white swath of accumulated ice, contrasting sharply against the otherwise green landscape. It’s as if the cloud disgorged a literal torrent of small ice grains, a “thump” not unlike a massive, localized snowfall.
Snow removal equipment can be required to clear it.
The pictures and descriptions of the Guadalajara storm seem to fit the bill of a typical SPLASH event.
SPLASH events occur in different regions of the United States, and according to a scientific study by Matthew Kumjian at Penn State, there is no explanation why one storm may produce extremely large hail, and another storm generates extremely large amounts of small hail.
Satellite views of Sunday’s storm show a couple of lone thunderstorm clusters in the vicinity of Guadalajara. These most likely contained multiple “feeder” cells that repeatedly circulated pockets of small ice embryos into updraft portion of thunderstorms where hail initiates.
Hail is somewhat unusual in southern areas during the summer because the distance between the freezing layer in the cloud and the hot land surface is large so the ice can melt before reaching the ground. But, because Guadalajara sits near the mountains at an elevation over 5,000 feet, this distance is reduced and hail is more common.
Sunday’s thunderstorms no doubt unloaded vast amounts of both rain and hail. But while some media reports indicated six feet of hail fell, the actual accumulation — while substantial — was probably a good deal less than this.
The dramatic piles of hail shown in the pictures and videos probably reflect “banking” of ice by flowing water. Rain water coursing through streets and alleys likely piled up the ice, which floats on the water, into massive accumulations along and around ground obstacles such as vehicles and buildings.
Rather than dumping six feet of hail in one place, “these enormous
#hail drifts are almost certainly the result of an urban flash flood during hail-producing thunderstorm, which washed huge volumes of hail ice from around city into culverts & low-lying areas,” tweeted Daniel Swain, a climate scientist at the University of California Los Angeles.
Such events have happened before — even right in Mexico. In August 2014, we reported on “two to three feet of hail” that piled up in Mexico City during a torrential storm. “[P]arts of the low latitude city appear transformed into a winter wonderland in the dog days of August,” we wrote. The scenes, while not quite as impressive as Guadalajara’s Sunday, were similar:
In April 2012, we showcased “chest-high hail” in the Texas Panhandle after storms erupted over the region:
In other words, while rare, the Guadalajara event had precedent.
After Sunday’s hail event in Guadalajara, Jalisco Gov. Enrique Alfaro remarked to the AFP, “Then we ask ourselves if climate change is real. These are never-before-seen natural phenomenons. It’s incredible.”
But any link to climate change is currently a stretch, although that may become clearer in the future.
In an essay posted last month, meteorologist Paul Douglas concluded “there isn’t solid evidence that hail has increased due to climate change” after interviewing four experts on the matter. There’s simply neither sufficient data to support an increase nor a strong theoretical foundation to expect one. The experts, however, posited “a warmer, wetter world should increase hail frequency and size” in some areas, Douglas wrote.