A year ago today, the day started with the federal Storm Prediction Center including much of Western New York in an area it considered under a "slight" risk for severe weather, with a 2 percent chance for a tornado and a 15 percent chance for damaging wind and hail.
Twelve hours later, the first of four tornadoes struck.
The strongest one — rated 2 on a scale of 0 to 5 by the National Weather Service — tore a 6.1 mile, 700-yard wide path between Locksley Park and Chestnut Ridge, striking the Hamburg Fairgrounds in between, damaging buildings, trees and cars. Other weaker tornadoes touched down in Wales, Houghton and Angelica.
But the tornadoes also left clues for weather experts.
A pair of four-tornado July days – separated by seven years and four days – were spawned by what meteorologists call a mesoscale convective vortex - a storm system created by a rotating center of low pressure in the midlevels of the atmosphere. The “MCV” could be nature’s biggest hint yet about when the Buffalo Niagara region is most susceptible to severe thunderstorms that could spawn tornadoes.
“It’s probably the biggest takeaway from this,” said Jon Hitchcock, a meteorologist at the weather service’s Buffalo office.
The vortex is born from the remnants of thunderstorms and can survive for 12 to 18 hours after its parent thunderstorm has dissipated, federal forecasters said. The low pressure center, which can even take on a hurricane-like appearance, draws winds in toward its center in a circular pattern, creating favorable conditions for lift in the atmosphere. Then, if the right convective ingredients feed into the circulation – namely, heat and moisture – it destabilizes the atmosphere, creating the potential for strong wind shear and severe thunderstorms like the supercell that spawned tornadoes between Hamburg and Angelica last year.
When last year’s tornadoes hit, forecasters thought of July 24, 2010.
That afternoon, a pair of tornadoes with wind speeds near 125 mph tore through Mayville and Randolph. Two weaker tornadoes packing winds of 95 mph touched down in Great Valley and Allegany.
The origins of those storms – and last year’s tornadoes – were clusters of thunderstorms that struck parts of the Midwest as far away as Iowa, the previous day.
Tornadoes are rare occurrences in Western New York, so forecasters try to pick apart the data for clues.
“We review all the severe weather cases,” Hitchcock said.
The Erie County Department of Homeland Security and Emergency Services did its own review after last year’s tornado that caused more than $3 million damage to the fairgrounds’ buildings, grandstand, trees and cars. Among the lessons:
- A tornado can come without much warning.
- Equipment like tub tree grinders can be useful.
- Intramunicipal cooperation at the local, state and federal levels is essential.
“We got up in Air One and got a quick assessment of the entire area,” said county Emergency Services Commissioner Daniel Neaverth, Jr.
In the sheriff’s helicopter, he examined the path – and extent – of debris with Judith Levan, the meteorologist-in-charge at the Buffalo office of the National Weather Service. That immediately helped emergency officials coordinate management plans with highway crews, utility companies and law enforcement, Neaverth said.
What emergency officials also learned first hand was how wildly unpredictable tornadic storms can be.
The Storm Prediction Center of the National Weather Service circled Western New York as a location for the possible development of severe thunderstorms, but it wasn’t until spotters in Hamburg started calling in with reports of a funnel cloud that the threat took on whole different meaning.
“Essentially, with current technology, it has to be on the ground,” Neaverth said. “They can’t always tell through the radar if there’s a tornado on the ground.
“Technology isn’t exactly as it’s portrayed on the TV shows.”
Hitchcock said a weak tornado touched down near Locksley Park in Hamburg but its signature wasn’t picked up by radar until a short time later after it gained strength.
— David Church (@warmbias) July 20, 2017
Tornado warnings were sounded for Hamburg, and then three other times over the next couple of hours as a single supercell tracking from northwest to southeast spawned four tornadoes between the Lake Erie shoreline and Allegany County. Luckily, no injuries were reported in any of the four tornadoes.
Weather service and emergency officials said the public likely learned something too on July 20, 2017: the importance of heightened awareness.
“Be prepared, when even in a slight risk of severe weather,” Hitchcock said. “Go over your safety procedures.”