Weather in minute detail

obmar · Weather in minute detail

07/01: Weather in minute detail

BY Brent Killackey
Journal Times

When National Weather Service meteorologists watch the radar, they’re not just looking at raindrops — they’re sometimes looking at mosquitoes and dust particles.

Today’s Doppler radar systems are sensitive enough to pick up these tiny objects and seeing them helps meteorologists pick up subtle boundaries between warm and cold fronts or other weather phenomenon, according to Jeff Kraven, science and operations officer for the National Weather Service’s Sullivan office.

These multimillion-dollar Doppler radar systems also give meteorologists an impressive look inside powerful storms, pinpointing the formation of hail or wind rotations that could lead tornadoes.

While television stations commonly have their own Doppler radar, they’re often older military radars that have been upgraded to Doppler capability, Craven said.

But television stations can tap into the data from the National Weather Service.

The National Weather Service office in Sullivan covers 20 counties in southern Wisconsin. That’s a fairly small territory for a National Weather Service office, considering there are 122 across the country. But southern Wisconsin is pretty dense in terms of population. Other Weather Service offices in Wisconsin include Green Bay and La Crosse. Parts of northwest Wisconsin are covered by Minneapolis and Duluth, Minn., offices.

The first

WISN-TV (Channel 12) began tapping into National Weather Service radar systems this summer, augmenting their single Doppler radar — which is atop Community Memorial Hospital in Memomonee Falls — with data from four National Weather Service radar systems in the region.

“What it can do is really give you minute details inside a thunderstorm, meaning we can see hail forming inside a storm — a lot of times we can tell how big hail is developing in a storm,” said Channel 12 Chief Meteorologist Mark Baden.It can also provide a tornado vortex signature. That’s a term for the rotation identified in a storm that could produce a tornado.

“We’re at the peak of where things are right now, technologically speaking,” Baden said.
The sharing of National Weather Service radar isn’t anything new — that’s been done for 15 years, Craven said.

But software and other technology allows television stations to use raw data from the radars, using their own software to create their maps and analyze the information.

Those same technological advances have boosted the capability of what the National Weather Service uses and sees to issue watches and warnings.

How much, how fast?

But what you see on TV is just a small amount of the data and tools used by National Weather Service meteorologists to analyze storms and issues watches and warnings.

The Doppler radar used by the National Weather Service takes about 4 or 5 minutes to completely scan the skies, providing many layers of data.

That’s an improvement over just a few years ago, when computer technology and bandwidth was such that it took 6 minutes.

“That minute or two may not seem that much, but that can be that much lead time on a tornado or flash flood,” Craven said.

The National Weather Service has been using Doppler radar, which can measure not only the intensity of a storm, but the wind currents within it, since the early 1990s, Craven said.

Why does it take 4 or 5 minutes to scan the skies?

The radar sweeps around 360 degrees at one level, raises one-half a degree and sweeps 360 degrees, and continues raising upwards about 20 degrees. That enables the radar to take slices of the sky, peering into storms at not only ground level, but higher up where hail is forming.

If the radar spun faster, the data wouldn’t have the resolution needed to see tornadoes and flash floods. Some of it’s hardware, but there are software and communications bandwidth restrictions impacting the time it takes to gather that picture of the skies.

How high?

The real key to severe weather is not only surface conditions, but many miles in the atmosphere, Craven said.

What people traditionally see on weather Web sites, including the National Weather Service site at http://www.noaa.gov is the lowest slice of data, Craven said. “That would be the one closest to the ground,” he said.

“You’re probably looking at 5 or 10 percent of the total available products in a Weather Service office,” Craven said of what’s available to the public. But the more advanced data and products require expensive equipment and advanced training to use and interpret what’s being seen.

On June 13, the National Weather Service launched a new Weather Research and Forecasting Model. It’s a computer program that supercomputers will be using to help forecast weather. It’s hoped it will provides improved details on hazardous weather, such as flooding, severe thunderstorms and winter storms. Craven said the new model has been in testing for four to five years.

The future

The next phase of Doppler radar is dual polarized Doppler radar. This radar will have an easier time distinguishing between torrential rain and hail.

“This new radar will be able to tell the difference between a circular hailstone and this lens-shaped raindrop,” Craven said. “This will prevent us from issuing a false-alarm flash flood warning when it’s really a hailstone.”

It’s also better at telling the difference between rain and snow.

Ten to 15 years down the road, depending on budgeting, the National Weather Service hopes to upgrade to phased array, a type of Doppler that doesn’t have any moving parts, Craven said. That makes maintenance easier and less costly. This radar, which is used in the military, uses electronic beams that can be instantaneously directed in just about any direction.

“Also, it will be able to scan the skies probably every minute or so,” Craven said.

Depending on federal budgets, a new series of weather satellites will be launched in 2012. These satellites will provide more frequent images in higher resolution and will be able to detect lightning across the globe. This will help evaluate the potential for severe weather, whether hurricanes and tornadoes to flash floods and snowstorms.