Radar signatures improve tornado predictions

Anna Hocking was high atop a metal ladder near Harrow when the rain came pelting down. Soon, the deluge turned into toonie-sized hail that clattered among the radar antennae where she and Wayne Hocking were assembling the newest in an Ontario-Quebec network of radars.

As the pair clambered to safety, they knew it was clearly more than a severe thunderstorm; how much more, they discovered only later, when they learned an F1 tornado had touched down about a kilometre away.

Ironically, the Harrow installation – under construction that day in June 2008 as only the second array in the Ontario-Quebec Windprofiler Network – could have been of use in pinpointing and forecasting that very tornado.

According to recently released research by the Hockings, radar-based calculations of wind-speed and turbulence can be used to buy 20 minutes more warning time of an impending tornado – critical information when mere seconds can save lives.

Debora Van Brenk // Western NewsAnna Hocking, PhD’98, and Physics and Astronomy professor Wayne Hocking, who leads the Atmospheric Dynamics Group at Western, have developed a methodology to forecast a tornado with 90 per cent accuracy within a 100-kilometre radius.

Their paper, Tornado Identification and Forewarning with VHF Windprofiler Radars, was published last week in Atmospheric Science Letters, a journal of the Royal Meteorological Society.

Lead author Anna Hocking, PhD’98, and Physics and Astronomy professor Wayne Hocking, who leads the Atmospheric Dynamics Group at Western, said this methodology can forecast a tornado, with 90 per cent accuracy within a 100-kilometre radius.

“We have found signatures in wind speed and turbulence that, when used with other tools, can accurately forecast the formation and location of a tornado before it happens,” Anna Hocking said.

Accurate, timely and geographically precise tornado warnings have long been a Holy Grail among meteorologists. Sometimes, proprietary technologies and differing methodologies among forecasters have proven a barrier to deciphering weather patterns.

“Typically, meteorologists look for specific signatures that include wind speeds plus an overshoot, a dome-like knob that forms atop a thundercloud,” said Anna Hocking. “What we’ve been able to do, for the first time, is add in and quantify a third factor: turbulence.”

The pair uses a unique Ontario-Quebec network (O-Q Net) of purpose-built radars that measure high-altitude wind and turbulence through the upper atmosphere, troposphere and lower stratosphere. The VHF radars detect reflections from puffs of turbulence in the upper atmosphere, with signals not getting buried by precipitation, birds or insects, as some radars might.

The O-Q Net of 10 radar arrays (including one just north of London) was built in part with funding from the Canadian Foundation for Innovation, as well as Natural Sciences and Engineering Research Council of Canada and Environment and Climate Change Canada. The network also involves collaboration with researchers at York and McGill universities.

“Because this network is so large and is designed to measure turbulence as well as winds, we’ve been able to see patterns, predictors, that haven’t been evident before,” said Wayne Hocking, who is also a Fellow of the Royal Society of Canada.

The array is intended to detect severe weather, but it was Anna Hocking who first noticed distinct patterns and hypothesized they might be tornado precursors.

The Hockings collected and analyzed 16 years of tornado data, including reports to Environment Canada from citizen observers. “We couldn’t have known these tornados had touched down if they hadn’t seen them and reported to Environment Canada,” Wayne Hocking said.

They correlated those reports with real-time and archived data from the radar network.

Of the 31 documented tornadoes, specific profiles of cloud overshoot into the stratosphere, wind velocity and turbulence were uniquely present 90 per cent of the time – with all three signature features evident 10 to 20 minutes before the tornado formed. There was less than a 15 per cent likelihood of false detection.

That’s a significant improvement over existing predictions, with warnings that often cover huge regions and can produce false alarms.

Some storm hunters use portable radars as they chase and predict tornados, Wayne Hocking said.

The O-Q WindProfiler network uses the opposite approach, he said.

“Our strategy has been more like a spider web. We spread out the web in the form of these radar arrays across two provinces and wait for the fly – the tornado – to arrive.”

He said the intent is to use and build out this technology to complement other forecasting methodologies.

“We’re not in competition with Environment Canada. We’re trying to work with them, to narrow down predictions to specific spots, within 20 minutes of the event.”

Maintaining the network remains an issue, with two of the 10 arrays having been shut down and the London antennae out of commission until repairs take place early next year.

The Hockings are confident their analysis provides a convincing argument for improving public safety through early forecasting.

“There’s still a lot to be done and we’re not going to say this is going to solve the whole forecasting problem – but this is a large step in the right direction,” Wayne Hocking said. “The data suggests we now have a more reliable tool for forecasting than has been possible before this.”