Marble-Sized Hail: Our Two Cents

Every year, thousands of people report hail from coast to coast, but there is one type of hail size often reported that is not useful for meteorologists and can effect warning information and, later, possible insurance claims.

Most reports come in with a size as you would see it on a ruler in inches, and other reports come in using an object such as a ping pong ball, pea or baseball. The National Weather Service has a list of hail size descriptions that roughly equate the two. 

Unfortunately, many storm reports and similar lists have marbles listed as a hail size equivalent.

(MORE: Hail an Underrated Danger)

In the game of marbles, there are two distinctively different sizes of marbles used in a game: a shooter and a target. The shooter, according to the National Marbles Tournament rules, must "not more than three-quarter inches in diameter and not less than one-half inch in diameter." Target marbles should be five-eights of an inch in diameter, according to the tournament rules.

Outside of legalities, marbles can be as large as 3 inches in diameter or as small as peas. 

Well, which size of marble is your hail stone? 

This is tricky for those of us that receive hail reports to decipher.

Hail becomes severe when it is 1 inch or larger in diameter, or about the size of a quarter. 

When marble-sized hail is reported, we must decide if it's a big marble or small marble, and how big of a big marble it might be. It makes a difference.

In the image above, the marble on the left meets severe thunderstorm criteria along with the quarter, but hail that falls in the size of the other objects is not severe.

According to Keith Stellman, meteorologist in charge at the National Weather Service (NWS) in Peachtree City, Georgia, "the hail reported to us as marbles will go unreported since we don't want to assume."

When a report like this is sent to the NWS, according to Rick Smith, warning coordination meteorologist at the NWS in Norman, Oklahoma, the person on duty has to spend a little extra time trying to clarify the report to determine if it's severe or not. This can determine whether a warning is issued, and it lessens lead time for those in the path of the storm  if the report comes in as the storm is occurring. 

(VIDEO: How Does Softball-Sized Hail Form?)

Often pictures don't help that much when comparing a hail stone and a marble. The comparison is greatly lost when two objects are of unknown size. 

We encourage measurement of hail stones – when it is safe to do so after a storm passes – using a ruler or tape measure. Hail stones are measured in diameter, or from one end of the object to the other.

Smith said the NWS needs more hail reports. "They help us issue better warnings and give us details about what's actually happening where you live that no radar can," he said.

Other comparison objects that don't help meteorologists all that well include your hands, cell phones and oranges. These objects all can vary in size and shape. A few other reports that have been sent into the NWS are listed below and are generally not useful.

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How You Can Improve Reports and Why It's Important

The most helpful objects are coins, but regulation size sports objects such as golf balls and baseballs are also helpful for larger hail stones. 

There are other objects that you can compare your hail to if you don't have a ruler. Some of these include limes, lemons, Coke bottle caps, contact cases, lighters, dollar bills, DVDs and billiards balls. These objects are all standard-sized objects and are helpful to meteorologists if you cannot find coins. 

You can assist meteorologists by sending your reports of hail, and other kinds of severe weather such as flash flooding, tornadoes and damaging winds, through the mPing app for iPhones and Androids and through the spotter network.

Smith also advises anyone to report through NWS local web pages. Most offices have places on their websites to report severe weather. 

(MORE: Star-Shaped Hail Breaks California Record)

Many weather service offices look at hashtags such as #GAwx (Georgia weather, for example) for storm reports.

You can send your reports to us on our Facebook page and Twitter. 

"The benefit of social media is seeing photos or videos of the weather," said Steve Nelson, science and operations officer with the NWS in Peachtree City.

Report the largest hail stones that you can find. According to Bryan Wood, meteorologist for Assurant, hail reports received by the NWS may not represent the largest hail that fell in a storm. 

In one hail study, called Project HailSTONE, scientists from the NWS office in Pleasant Hill, Missouri, found that hail stones size was under-reported in NWS reports from the public (Storm Data).

The project found that for 44 thunderstorms the maximum hail size in those thunderstorms was 2.25 inches (or bigger than hen egg-sized) while reports that came in from the public on those storms indicated that the biggest stones were 1.75 inches in diameter (or golf ball-sized). 

This under-reporting may mean the difference between penny-sized "marble" hail vs. a severe-sized "marble" in the end. 

"One key thing people need to know," said Stellman, "is that insurance companies use our official reports that are submitted to National Climatic Data Center (NCDC) and StormData when determining claims. In a case where a customer is disputing when hail might have occurred, if there is no report of it, then it will be harder for them to win a claim."  

"That may not seem like much, but that means a 200 percent increase in kinetic energy on impact. That’s a big deal when you’re looking at roofs being damaged," Wood said.

According to a Swiss Re report, two severe hail storms in Texas alone caused $4.77 Billion in insured losses in 2016. 

Don't eyeball hail stones out your window as it falls. "When [hail is] accompanied by strong winds, it can rip apart siding and shatter windows, which increases the danger and makes damage much more costly," Wood said.   

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