Gustnadoes Stir Up a Storm in the World of Meteorology

CHICAGO — Bong. Bong. Bong.

The urgent tones issuing from the television set signaled a call to pay attention. While a cheery Weather Channel forecaster pointed to a map of Florida, crawling across the bottom of the screen was a message, fraught with exclamation points, for local viewers: “Abandon all mobile homes! Take cover immediately!”

Outside, sirens blared.

Gustnadoes whirled upon the land.

Gustnadoes had been sighted, dozens of them.

Gustnadoes to the west and south!

Gustnadoes?

The National Weather Service is almost sorry it used the term to justify the alert called here on a stormy mid-May evening.

“After we put out the statement, we had so many questions and got so many phone calls that we had to follow up with another statement explaining what exactly is a gustnado,” said Jim Allsopp, a forecaster at the Weather Service’s office in Romeoville, Ill.

As a result, even the cyclone-savvy denizens of the nation’s Thunder Belt learned a new thing or two about twisters. “Gustnado,” cited this year by meteorologists here, in New Jersey and in Oklahoma, appears destined to enter the public lexicon.

A gustnado is a sort of stealth tornado, a weak sister that sneaks in without the usual signs. Radar can’t detect it. Unlike a mesocyclone--the scientific term for that thing you saw in “Twister”--it doesn’t need a super cell, a well-organized system with circulating winds present in roughly 5% of all storms.

It moves ahead of a developing storm, on the “gust front”--hence the name, slang for “gust-front tornado.” It is caused by a wedge of cold air pressing down on rising warm air, forcing the warm air to spurt forward and spin.

A gustnado spirals up from the ground, not down from the clouds. It stretches a few hundred feet, far from the miles-high size of a classic tornado. Its energy rates a mere 0 or 1 on the 5-point Fujita scale (the cyclonic counterpart to the earthquake scale).

A gustnado lasts from mere seconds to five minutes or so, as compared to a typical tornado life of anywhere from 15 minutes to hours on end.

It looks . . . well, it looks like a tornado. And although it won’t carve a path of massive destruction or send fictional farm girls to Oz, its rotating winds are capable of knocking down a tree or ripping the roof off a house.

And “they are very common,” said James W. Wilson, senior scientist at the National Center for Atmospheric Research in Boulder, Colo.

In the course of studying thunderstorms, he has witnessed gustnadoes in Colorado and even in California’s San Joaquin Valley. Florida, he added, is apparently Gustnado Country too.

Let it be pointed out that Wilson winces at the term “gustnado.” (He prefers “non-super cell tornado,” which hardly trips off the tongue.) But he may have been the first to use gustnado in a journal article.

In the February 1986 issue of the Monthly Weather Review, Wilson noted the name catching on among storm chasers who had first spotted these strange, brief tornadoes where no tornadoes should be.

Whether to issue public warnings for gustnadoes is “kind of controversial,” Wilson said. “You probably could put out warnings that tornadoes would likely be weak. But you still want people to take precautions.”

In Chicago, a desire for accuracy won the day. From the western outskirts of the metropolitan area, people telephoned police and meteorologists with reports of funnel clouds and touchdowns.

Even out a window of the Weather Service office, a swirling dust cloud was clearly visible.

Allsopp, off duty and outside his home, was talking with neighbors who pointed out what they thought were funnel clouds in an ugly sky the color of a bruise.

“It’s not that kind of storm,” Allsopp told them. “But I wouldn’t be surprised if the sirens went off.” Sure enough, within seconds, the wailing began.

When reporters started calling to find out just how many tornadoes had hit the region, the forecaster on duty felt compelled to avert what seemed to be a barely stifled panic.

The time had come for gustnadoes to make their Chicago debut.