Just picture this – it’s a warm, spring or summer afternoon and a thunderstorm starts to roll overhead. You head indoors and hear rain begin to fall. As the cracks of thunder get louder and that rain heavier, you peek out the window to see large chunks of ice on the ground…
Hail is something we all are most likely familiar with, but it is a pretty strange concept when you start to think about it.
“Hail is one of those things that we don’t really know how it forms,” says Sean Waugh, a research scientist at NOAA’s Severe Storms Laboratory.
“In general, you need moisture and a strong updraft – basically vertical motion in the atmosphere that pulls that moisture up from the surface and holds it aloft. As those temperatures get colder the higher up in the atmosphere you go, that moisture turns to liquid water and eventually to ice. And then that ice can continue to grow and accumulate mass as it’s essentially lofted around inside the storm.”
Eventually, the stone becomes too large for a storm's updraft to hold, so it tumbles to the earth below. Waugh adds that there are some other factors to consider here, too – including wind shear. That’s the change of wind speed or direction as you move up in the atmosphere. He says that can influence where hailstones fall near a storm. The amount of moisture available within a storm can also impact how dense hail that makes it to the ground is.
But Waugh says that’s kind of all we know because there’s one big problem when it comes to observing hail for study and research...
“All of our observations basically as long as we’ve been doing hail research is post-impact – meaning that the stone falls and you collect it maybe 20 minutes later, 30 minutes later after it’s had a chance to melt. We don’t know what broke when it landed, how much of that mass, or size or shape have we lost between when it fell and when we find it, right? I’ve seen six-inch diameter stones melt before I can get out of the car to pick them up, so we know this is occurring,” he explains.
There are other questions, too: how fast does hail fall? Does it fall in a specific orientation? Does the stone melt while it’s falling to the earth below?
“These are all really, really important questions if you’re trying to ascertain what hail looks like to a radar. And that’s a really critical piece of knowledge if you’re trying to warn for hail in real time, which is obviously the goal! Most people want to know if there’s going to be golf balls falling at their house or softballs,” Waugh says.” “There’s a very big difference between those.”
So, to potentially help answer those questions, Waugh and his team have built a system that observes hailstones in free fall and in real time.
“It uses 4K cameras that shoot frames at 330 frames a second. And in order to do that, we only expose each frame for about 75 microseconds. This allows us to capture that object in a perfectly still, very sharp image, but we need a lot of light to do that. Otherwise, the image would just be dark,” he explains. “So the LED array I have on the back of the truck produces about 30% more light than the sun! You actually need eclipse glasses standing behind the vehicle to look at it.”
Waugh says the project is already producing some incredible results, as you can see here:
Ok, so now we’ve got a system to observe falling hail, but that’s only part of the equation, Waugh says.
“Believe it or not, it may actually be a lot harder than you think to try and position a system intentionally in front of a storm that you hope is going to produce large hail so that you can study it. We don’t hope that it does it because that, obviously, causes a lot of damage and destruction to the surrounding property, crop fields and infrastructure. But if it’s going to happen, we want to be there to observe it and learn from it. But it’s really challenging to get the vehicle into the right spot to do that.”
Waugh says his system will be used for years to come to conduct this research – hopefully with more vehicles in more places to capture additional imagery and data – gaining more knowledge about the storms that produce hail.
“We can use that knowledge to improve our forecasts of what storms are likely going to produce hail days in advance. By understanding the type of hail that different storms produce, that increases our ability to model it properly and then forecast that in the future,” Waugh explains. “In a more immediate aspect, knowing what type of hail is falling and comparing that back to radar observations, we can improve that warning process. So, when the National Weather Service employees are looking at a storm and trying to decide what kind of hail is going to fall – we’re working off of data that’s sort of incomplete because we’ve only been looking at hail on the ground. If we have those observations in real time, we can improve that warning, decision making process – make those warnings more accurate and timely. And that way people can take appropriate action to protect life and property.”
You can find more information about all of the life and property saving research that NOAA and the National Severe Storms Laboratory are working on here.
It's Virginia Hurricane Preparedness Week
The state’s Department of Emergency Management, in partnership with the National Weather Service, says this is the week to start taking proactive steps ahead of the Atlantic hurricane season.
During Virginia Hurricane Preparedness Week, there are several things state and federal officials are hoping to remind Virginians of – including knowing your risk when it comes to tropical systems and how to prepare an emergency kit.
That comes as the National Hurricane Center is preparing some new products for the upcoming season. It and the Weather Prediction Center – both part of NOAA – are set to highlight areas that are at risk of heat impacts because of power outages following a tropical storm or hurricane through a new online tool. That data will also be used in public advisories and other messaging from the National Hurricane Center.
Both state and federal officials say this year’s Atlantic hurricane season – set to begin on June 1st – is looking like it will be an above-average in the number of named storms.
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