Six short-lived EF1 tornadoes which tore through northern Illinois during the last part of June might have been all but invisible to the National Weather Service had they not updated their systems earlier that month.
The closest touched down briefly between Plainfield and Romeoville. According to Matt Friedlein, a meteorologist with the National Weather Service’s Romeoville office, the tornado was “embedded” in the storm front. Another tornado happened near Morris.
“All of the tornadoes happened in less time than the old radar scanning strategy takes,” Friedlein said.
Atmosphere scans by the weather service’s Doppler radar— the massive white bubble that towers over Lewis University Airport — once took about five minutes to complete. The Doppler — basically a rotating radar dish enclosed by the bubble — used to progressively scan the horizon from 0.5 to 19.5 degrees.
The Plainfield-Romeoville tornado was on the ground for less than three minutes, a short enough time to form and dissipate in-between scanning intervals.
The new system, which was installed in June at the Romeoville office, scans lower elevations every 1.8 to 2.5 minutes. The name of the new system is Supplemental Adaptive Intra-Volume Low Level Scan or SAILS. It emphasizes scanning at elevations 0.5 to 3.1 degrees, which is the area where tornadoes touch down.
According to Friedlein, air movement itself is invisible to Doppler, the radar can see which way raindrops or hail are moving within a storm.
The system was less than a few weeks old when it was put to the test for the two June 30th storms. The powerful bow-shaped fronts, known as derechos, caused widespread damage in Will and Grundy counties.
Also new for Doppler is a radial noise filter that removes solar interference known as “sun spikes” from radar images, according to the National Weather Service. Another new feature will enable the radar to automatically determine the best settings for viewing velocity data for the strongest storms in the radar’s coverage area.
But technology only can go so far. Forecasters still rely on weather spotters for data.
“The technology is great, but we’re not at a point where we can see everything 100 percent,” said Harold Damron, director of Will County Emergency Management Agency. “It’s definitely a combination of eyes on the street and technology working in concert with each other. We get eyes-on reports from law enforcement, firefighters or other types of spotters stationed out there and feed them into the weather service. It allows them to correlate what we see with what they see on the radar.”
Jeremy Hylka, director of the Joliet Weather Center, agreed.
“As much technology as we have, nothing beats the eye from a spotter in the field,” Hylka said. “It goes without saying.”
One great advancement has been the ability to narrow down the geographic focus of weather warnings, Damron noted. In years past, severe weather and tornado warnings would be issued on a countywide basis.
Meteorologists now can define a specific warning area on-screen and issue a warning with the click of a mouse, Friedlein said.
The weather service now can issue Wireless Emergency Alerts to cellphone towers in an affected area, which in turn will broadcast an audible noise and warning text to all newer smartphones within its range.
Damron said he got a clear view of the limitations of the older technology during last year’s anniversary of the Aug. 28, 1990, Plainfield tornado, when he viewed a black-and-white radar image of the storm.
“It was just a shock to look at it on the traditional round radar screen,” Damron said. “It’s amazing how far we have come.”