Why is Colorado one of the most susceptible places for large hail?

WeatherNation TV

It seems crazy that softballsized chunks of ice would fall from the sky on a midsummer afternoon. So what makes summer hailstorms so severe? And what causes hail?

Hail basically is a tug-of-war between rising winds and gravity. Warm, moisture-rich air is the main fuel source for thunderstorms. The warm air is absorbed into a storm through the rapidly rising wind, known as an updraft, which powers the whole system.

The rapid-rising motion from an updraft forces water molecules (rain) and water vapor to get sucked up to heights where the temperature is freezing, turning water into ice. Between those updrafts, a hailstone will drop and absorb more water around it, before another updraft pushes it back up to the freezing level and adds another ring of frozen water to the hailstone.

This up-and-down motion continues until the hail grows large enough that the updraft can’t support it. That’s when gravity takes over, forcing the hailstone to fall to the ground. It takes an exceptionally strong updraft to get a hailstone to the size of a golf ball, grapefruit or softball.

To create a hailstone the size of a softball, it takes an updraft of about 98 mph, according to figures from the National Weather Service. To put that into perspective, that’s equivalent to the wind speed found in an EF-1 tornado or a Category 2 hurricane. It’s extremely rare, even in Colorado, and it typically is caused by an unusually high amount of energy fueling a storm.

A massive hailstorm rocked the Colorado Springs area this week, smashing car windshields throughout much of the city’s south side and injuring at least eight people.

The temperature rose to nearly 80 degrees in Colorado Springs on that Monday afternoon, a warm but not exceptionally hot reading for the heart of summer. That sort of heat alone won’t serve as a trigger for a severe hailstorm. What stood out about the conditions on that day in the Colorado Springs area were unusually high dew points — a measure of the amount of moisture in the atmosphere. Thanks to a moisture-rich easterly upslope wind, dew points rose to about 60 degrees that day, a figure seen only a handful of times each year on the usually dry Front Range.

The forecast from the NWS office in Pueblo that day warned that Convective Available Potential Energy values could top 2,000 joules/kilogram, showing an unusually high degree of energy for the area. These figures also helped cause the Storm Prediction Center, the governing body for severe weather, to bump up the Front Range’s severe weather outlook to a “slight risk,” noting in its discussion “a mixture of supercells and multicells capable of large hail and damaging winds” in its Colorado discussion.

Finally, the relatively cool conditions, at least for summer standards, in turn meant freezing levels above the surface were only hovering at about 11,000 to 12,000 feet, a low figure for the middle of summer. That meant updrafts had a shorter distance to get water droplets to the freezing level and less distance between the freezing level and the ground for the hail to melt in.

From a broad perspective in Colorado, we are extra-prone to large hail for one reason: Our elevation. Denver’s mile-high altitude places it 5,280 feet closer to the freezing level than a sea-level location, giving us somewhat of a head start in getting those hailstones to the freezing level and making us one of the world’s most susceptible locations in the world to large hail.

Also, because we’re closer to where hail actually forms, it has less time to melt before reaching the ground. It’s like eating an ice cream cone right away as opposed to a minute or two minutes after you order it.

That combination of broad, natural geographic conditions paired with an unusually high energy supply makes Colorado susceptible to destructive hailstorms that can go down in the history books.