A dose of common sense from Marshall Shepherd
As I browsed the social media, I saw claims of climate change, “end of times” language, and sheer awe that hail fell in Mexico during the Summer. I thought that it would be instructive to provide context and perspective on this event before things get too carried away.
Hail is not uncommon during the summer. In fact, it is quite likely. For many people, it is counterintuitive that large chunks of ice can fall from the sky during the hottest season of the year. Hail forms in cumulonimbus clouds, which are quite common during the warm season.
Later in the article he drills down into regional points.
It is not surprising that higher elevations would experience a greater number of hail days. Florida receives more thunderstorms than most states in the U.S., but “hail alley” Colorado, Nebraska, and Wyoming. These states receive 7 to 9 hail days per year according to NOAA because the freezing levels (32 degrees F or less) in those regions are closer to the ground. Guadalajara, Mexico sits at an elevation above 5,000 feet. Hail is not necessarily abnormal at this geographic location. What about the vigorous amount of hail seen in photographs all over social media?
And the real sanity check.
It was clearly a dramatic and extremely impressive event with major local impacts–but I think the physical characteristics have been fundamentally mischaracterized. I have no doubt there were 1-2 meter hail drifts in some spots (photos attest to that)–but those drifts were clearly created by flash flooding down streets and culverts in a highly urbanized area. (A strong clue are the cars stacked on top of each other–water did that, not hail!). Come to think of it, the physical constraints of a single storm dropping 6+ feet of actual solid ice would probably be prohibitive anywhere on Earth, I would think. I don’t know the exact numbers, but even just considering the amount of column water or the vertical forces required to loft that much solid water…well, suffice it to say it would stretch credulity.
Shepherd is a mainstream scientist, so the rest of the article puts the episode in consensus perspective, but without the hysteria, hyperbole that is so common these days.
I want to close by dealing with the climate change question. Even officials in Mexico were so stunned by the hail drifts that they mentioned climate change. It is quite common after extreme weather events for some people to say “see climate change caused this.” The other partner in this very familiar social media “waltz” is the”things happen naturally or are not unprecedented” narrative. Climate change is very real, and humans are a significant cause of our crisis. Virtually every credible scientific organization and peer-reviewed report affirms this point. A 2016 National Academy of Science report even explored the emerging science of attributing current extreme events to climate change. Concerning severe convective storms that produce hail or tornadoes (SCS on the graphic below), linkages are not nearly as compelling (right now) as they are for heatwaves, drought, extreme rainfall, and lack of extreme cold events