In an Instant the Tornado Had Formed

August 2, 2014
By

Weather is a funny science, but as radar and computer imagery has improved the prediction of the weather, most people are used to being well prepared for the slightest drop of rain.

Television stations inundate us with updates and cell phones beep out warnings frequently.

But when an F2 tornado hit Revere Monday morning, there were few warnings – and no tornado warnings. Most people simply thought it was a bad storm, or heavy rain, and went about their business.

Glenn Field of the National Weather Service (NWS) Taunton office said the service had been following the storm all morning. It had formed in the Dover area in Norfolk County and had high-level rotation, but nothing had seemed to be ripe for spinning at ground level in order to make the essential top-to-bottom connection required to form a tornado.

Then, Field said, in an instant – faster than radar imagery could record – the tornado formed by the Chelsea Street Bridge and came together inconceivably and unbelievably.

It ripped its way up Broadway and was over in three minutes.

Traditional radar captures images every four minutes.

Field said one image at 9:29 a.m. showed nothing.

The image at 9:34 a.m. showed the tornado.

A 9:39 a.m. image was again harmless.

“It wasn’t until the image at 9:29 a.m. that it showed it was beginning to come together, but not totally,” he said. “At 9:34 a.m. the image showed just tremendous signals – all of a sudden. It was 100 mph – 50 knots in one direction and 50 knots in the other – and situated on top of Revere. There was also a debris cloud on the image that showed us…clearly things being lofted in the air. That was 9:34 a.m. and the tornado had already begun and it’s the first time we had evidence of it coming together. By 9:39 a.m., the clouds are separated again and not together at all. It came together as fast as it came apart. It lasted around three minutes and we say it happened officially at 9:32 a.m.”

Field said the tornado likely hit some warm surface air that escalated the formation around the Chelsea Street Bridge in Chelsea. The storm needed warm air on the surface to form a top-to-bottom spinning cloud – and southeast winds coming from Boston provided just what it needed.

“Unlike the Midwest tornadoes we see that form and come downward, this one had rotation aloft, but needed a trigger at the surface,” he said. “That warm front that was around Revere provided enough surface spin to combine with the aloft spin and it formed. Without that warm front, it probably never forms. It’s actually something that probably triggered a tornado warning downstream in Essex County, but that wasn’t much help to Revere. It happened so fast that all we were able to have is a severe thunderstorm warning, which expired at 9:30 a.m. Nothing came together at 9:30, so that warning expired.”

Field said there was a 40 minute severe thunderstorm warning that began at 8:50 a.m. on Monday, but unfortunately those warnings don’t often get heavily reported on television and they don’t appear on cell phone weather warnings.

“Nobody’s cell phones go off for severe thunderstorm warnings, but they will go off for tornado warnings,” he said. “That’s unfortunate for Revere. We could have issued the tornado warning when it was over Dover, but that would have alerted Boston and Dedham and there wouldn’t have been a tornado there. It’s a fine line that we have to walk on. We were following the storm closely. It just suddenly spun up within one scan of the radar imagery. It lasted three minutes and was over.”

He said it is regrettable that there was no official warning, though he did say it’s probably a lesson for many to pay attention to thunderstorm warnings.

“There were 40 minutes of a severe thunderstorm warning prior to the tornado,” he said. “Going outside during that is something people could have prevented. If you were aware of the warning, you could have been inside…There hasn’t been a tornado in Suffolk County since 1950 so it’s definitely a rare event. We certainly wish we could have had a warning for an EF2 tornado, but the nature of New England tornadoes is that they’re very quick and very shallow. They are quite different than the Midwestern supercells that form and are easier to track because they’re on the ground for a long time.”

The tornado, he said, broke up just after Brown Circle – meaning that it beat its way the entire length of Broadway in three minutes.

According to the NWS official weather statement, the tornado had maximum winds of 120 mph and had a rating of F2, breaking down to F1 at many points. Its maximum path wide was 3/8 of a mile and the total path was two miles.

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