A new version of the well-known weather Doppler radar technology now gives meteorologists the ability to see storms from additional angles and provide a more accurate forecast.
While traditional Doppler radar images capture a one-dimensional picture, the new two-dimensional technique, called Dual Polarization or ‘Dual-pol,’ provides clearer short-term forecasting and a greater ability to detect tornadoes.
“Raindrops just look like hamburger buns with Doppler,” said NWS meteorologist Paul Schlatter, “Dual-polarization technology sends and receives energy that is oriented in the horizontal and the vertical. So you’re getting a two-dimensional picture of what type of radar echoes are actually out there.”
That means improved hail detection for severe thunderstorm warnings, including tornadoes, as well as rainfall estimation for flood and flash flood warnings, rain/snow rates for winter weather warnings and improving services in mountainous terrain.
Schlatter describes the tool as “just an extra piece of hardware mounted on the little dish that’s spinning that is doubling the amount of basic information NWS gathers.”
NWS began installing ‘Dual-pol’ last year. So far, 100 sites have been upgraded; 160 are expected to be up and running by next June.
The technology is becoming the eyes in the sky for meteorologists who can now figure out if high winds are really a tornado, an evaluation that meteorologists couldn’t make until the storm touched the ground.
It will show the size and shape of particles falling in a storm and will help detect hazards to aircraft such as icing conditions and birds.
Typical weather radars transmit and receive radio waves with a single orientation of the electric field. Dual-polarization radars emit radio waves that alter their transmitted pulse between horizontal and vertical polarizations. The additional information on polarization improves the precipitation rate measurement as well as identifying the type of precipitation (snow, rain, freezing rain and hail).
It won’t help with long-term forecasts, but it provides enough information that could save lives in real-time because forecasters can be more certain in their warnings for short-term weather, Schlatter said.
‘Dual-pol’ can deliver better rainfall estimates that can help NWS decide to issue a flash flood. In the winter, the radar can help pinpoint when rain turns to snow, sleet or freezing rain, giving emergency managers a heads up about road conditions.
“This will help us detect the difference between heavy rainfall that occurs in storms all the time and the debris that will kick up,” said NWS Director Jack Hayes. “Why does that make a difference? You can’t see a tornado at night.”
In March, residents in Branson, Mo., had a 25-minute warning that a tornado was on the way, unheard of with Doppler that may have provided a five-minute warning. ‘Dual-pol’ was installed in the Ozarks region just a few weeks before the storm hit.
“It’s becoming more and more rare that a surprise tornado occurs,” Schlatter said. “We don’t miss those anymore.”
Last October, ‘Dual-pol’ was able to forecast an historic snowstorm across the Northeast as heavy snow fell, Schlatter said. Hartford, Conn., was buried under 12.3 inches of snow, Hillsboro, Vt., got 21.5 inches and West Milford, N.J. saw 19 inches on what was supposed to be a mild late autumn day.
“Instead of relying on people to call in to report whether it was raining or snowing, ‘Dual Pol’ was able to make better informed decisions,” he added. “It was a rare fall snow storm that shut down airports for a while, and resulting in countless power outages.”
NWS is spending $57.5 million on this new tool with help from outside contractors, L-3 Communications and Baron Services Inc.
“Severe weather can and will threaten you at some point in your life. Knowing in advance that it is a threat, knowing in advance what to do when that threat comes allows you to act,” NWS’s Hayes said.