A summer hailstorm prompts inevitable questions on global warming

Global warming? Not so much, apparently.

Nonetheless, it's worth noting that scientists have observed that as average temperatures have inched up in recent decades, the jet stream has shifted poleward at a rate of 1.25 miles per year, at least between 1979 and 2001.

It's impossible to say how this shift bears on Tuesday's storm. The jet stream isn't exactly straight. It dips and rises in sine-wave fashion as it travels west to east around the globe.

But there are other reasons to think that a warmer world could have more hail.

According to NOAA, hail forms inside a thunderstorm when updrafts carry water droplets upwards into cooler air. They freeze high up and then travel back down with downdrafts. Then they catch another updraft, adding yet another layer of ice as they rise again into the cold.

This can go on and on, the hail stone growing with each trip into the freezing zone. A cross section of a hailstone will reveal growth rings like a tree. (Take a look at NOAA's photos.)

More intense storms are a common prediction for a warmer world. And to the degree that more powerful storms increase the probability of that droplet going up and down and up again — gaining ice mass with each trip — it's probable that hailstorms may be more intense in the years to come.

That was the conclusion of a 2007 study in the Proceedings of the National Academy of Sciences. Particularly, the authors note, storm severity increases as the temperature and humidity differences between distinct air masses at different altitudes increases. The cooler the air above relative to that below, the faster the hot air will rise, and the more intense the storm.

Then there's the phenomenon of large chunks of ice falling from otherwise clear skies. Spain was battered with such falling ice in 2000. And in 2006, a microwave-oven-size ice-ball fell from skies over Douglasdale, a suburb of Johannesburg, South Africa, the first such recorded case in Africa.

These large ice balls are apparently in a different league than your average hailstone. And they have their own designation: "megacryometeors."

A Spanish scientist, Jesus Martinez-Frias, who co-coined the term, has a website entirely dedicated to tracking them.

On his site, he says: "Atmospheric megacryometeors could be a new type of fingerprint (geoindicator) of Climate Change. Tropospheric Global Warming (and mainly Stratospheric Cooling) might be making the tropopause colder, moister and more turbulent, creating conditions in which ice crystals could grow, forming, unusually and much more recurrently, large ice conglomerations."

The troposphere – the part of the atmosphere closest to Earth's surface – is where most weather happens. The stratosphere is above the troposphere; that's where jet airlines fly to avoid most weather, and it's generally cooler. And the tropopause lies between.

As it turns out, summer hailstorms in New York City are more common than one might imagine. The Times has reports of hail falling in the region stretching back to the late 19th century. And yes, witnesses always say they've never seen anything like it.

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