New Research Links Radar Data to Tornado Intensity | NBC Connecticut

New Research Links Radar Data to Tornado Intensity

Meteorology is an inexact science – so few things in the field are 100 percent certain – though advances in Doppler radar have allowed for some important certainties.

As severe weather season is fast approaching, it's a good time to review some of the latest severe weather research.

For Starters: The Tornado Debris Signature

One certainty is known as the tornado debris signature, or TDS.

When identified properly on Doppler radar, the TDS is confirmation that a tornado has touched down. It may not still be on the ground at the time of TDS identification, but a tornado has definitely touched down.

Thunderstorms cause many types of severe weather, including hail, flash flooding, damaging wind and tornadoes.

The damaging wind can either be straight-line wind, which surges downward from a thunderstorm, or wind that moves in a circular pattern in a tornado.

Therefore, only wind from a tornado is capable of lofting debris several thousand feet into the air.

A National Weather Service WSR-88D radar in Norman, Oklahoma.

Dual-polarization Doppler radar can identify when it's not seeing just rain, but rather a mix of rain and debris.

This is a relatively new way of confirming tornadoes, only becoming operational across the majority of the country in 2012.

Before moving ahead, it's important to note that the majority of tornadoes do not have a tornado debris signature associated with them.

Thus, the major benefits of the research outlined below only work in the select cases when a TDS is present.

So, what's new?

Researchers at the National Weather Service in Jackson, Mississippi have found a strong correlation between the height of tornado debris signatures and the approximate strength of tornadoes.

Tornadoes are classified as weak (EF0 and EF1), strong (EF2 and EF3) or violent (EF4 and EF5).

Many studies have at least noted the potential for a relationship between TDS height and tornado strength, including Schultz et al. in 2012 and Bodine et al. in 2013.

Most recently in 2015, Chad Entremont and Daniel Lamb analyzed every TDS starting back in 2010, when dual polarization upgrades on the U.S. radar network started.

They used 181 TDS cases in which the height of the TDS was clearly identifiable.

The results were revealing.

June 2011 western Massachusetts supercell depicted by National Weather Service WSR-88D radar.

Supercells, which are discrete and easy to pick out on radar, showed a better correlation than quasi-linear convective systems (QLCS), such as a squall lines.

Almost all weak tornadoes, defined as either EF0 or EF1 strength, had TDS heights below 10,000 feet.

For supercell tornadoes of EF2 or EF3 strength, the TDS heights were mostly between 10,000 feet and 20,000 feet.

The majority of violent (EF4 or EF5) supercell tornadoes had a TDS height over 20,000 feet.

A squall line depicted by National Weather Service WSR-88D radar.

For a QLCS, such as a squall line, the TDS height did increase with tornado intensity, though the signal wasn't as clear because there was plenty of overlap.

What does this mean for Connecticut residents?

Meteorologists who are experienced at interpreting dual-polarization radar data can provide lifesaving information faster than ever before.

It is critically important that a meteorologist reviewing radar data knows how to properly identify a TDS, or else all bets are off.

Once a TDS is identified, confirmation of a tornado can be broadcast in real-time. No human is needed in order to make the initial confirmation.

With that said, the goal is always to warn before a TDS is observed – since by definition, a TDS means a tornado has already touched down and caused damage.

Oklahoma National Guard soldiers and airmen respond to a devastating tornado that ripped through Moore, Oklahoma, May 20, 2013.
Photo credit: U.S. Department of Defense

However, in some cases before dual-polarization, a tornado couldn't be confirmed under hours after dissipation.

Once a TDS is determined, a meteorologist can analyze the multitude of radar scans that flow in every few minutes.

With the height of the TDS determined, an approximate estimate of tornado strength can be broadcast in real-time.

The strength estimate will always be approximate until the traditional storm survey is done on the ground by the local National Weather Service office.

The real-time value lies in characterizing a tornado as potentially weak, strong or violent.

This estimate of strength provides guidance to those that need to respond to the emergency at hand.

Though people in the path of a possible tornado should always take shelter, regardless of how strong it may be, the ability to emphasize that a tornado may be strong or violent may further push people to take action.

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